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Due to recent pandemic, many disinfectant products have been out of stock in the supermarket including --> hand santizer, dettol body wash, wet wipes etc

I want to investigate to find out which ones are actually the most effective against killing bacteria

- Types of brands of body wash on inhibiting bacterial growth?? Dettol --> "Kills 99.9% of bacteria" and was sold out completely

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- Bacteria is a unicellular organism. Unlike plants and animal cells, bacterial cells do not have membrane enclosed nucleus, instead they have a Nucleoid region
- Bacteria reproduce through binary fission - duplicate so offsprings are clones of parents

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K nown as the control center of the cell, the nucleus is the most prominent structure found in Eukaryotic cells. Bacteria, being one of the Prokaryotes, lack one.

So if they don't have nucleus, what do they have instead? How do they process their genetic information?

Find all the answers to these questions by scrolling down below.

Structure of Bacteria

Bacteria are minute single-celled microorganisms under the domain Prokaryota. Interestingly, they are believed to be the direct descendants of the first ever organisms that thrive on Earth about 3.5 billion years ago.

While they seem to be invisible with the naked eye, under powerful microscopes, the structures within bacteria can be observed. Check out the 13 different shapes of bacteria here.

The following are some of the major structures found in a bacterial cell.

Bacteria are ubiquitous and can be found in almost every place in the planet - in the soil, water, plants, and even animals like humans. With such great adaptability, it is not surprising that they have evolved the ability to reproduce and survive without the structure that enabled their eukaryotic counterparts to do so.

References

- "What are Microbes?". Accessed September 19, 2017. Link.

- "Bacterial Flagella: Structure, importance and examples of flagellated bacteria - microbeonline". Accessed September 19, 2017. Link.

- "Molecular Expressions Cell Biology: Bacteria Cell Structure". Accessed September 19, 2017. Link.

- "About Microbiology - Bacteria". Accessed September 19, 2017. Link.

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Do Bacteria Have Nucleus? | Structure of Bacteria | Bio Explorer

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Known as the control center of the cell, the nucleus is the most prominent structure found in Eukaryotic cells. How about prokaryotes like bacteria? Do Bacteria have Nucleus? So if they don't have nucleus, how do they process their genetic information? Explore all answers to this question in this page.

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Bacteria in our lives - Benefits of bacterias in our lives

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Bacteria in our lives - Benefits of bacterias in our lives

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- There are many bacteria in human body
- For example, they help breakdown the food we eat, make nutrients available to us and neutralize toxins

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Microbes permeate not just the entire planet but are also found in large numbers in animals and humans. The first thing to learn about bacteria is that most are beneficial and do not cause disease. In fact, they play a vital role - in the environment, animals, and humans.

The human microbiota

An adult human is colonized with many hundreds of bacterial species, and the total microbial biomass in an average adult is around 0.2 kg. Bacteria and other microbes (like fungi and viruses) in the body make up the human microbiota. The majority is located in the gastrointestinal tract, but all surfaces in contact with the environment are colonized with bacteria, such as the skin, upper respiratory tract and genital tract. The microbiota co-exist with the human host and have many important functions, as described in this video.

Most bacteria are good for us

The bacteria in our bodies help degrade the food we eat, help make nutrients available to us and neutralize toxins, to name a few examples. Also, they play an essential role in the defense against infections by protecting colonized surfaces from invading pathogens.

When talking about both microbes and their genomes (DNA), the term microbiome is often used. Recently there has been an increase in studies of the human microbiome. It is becoming more and more evident that microbes are important for human health, but also disease development. Inflammatory bowel disease, gastric ulcers, colonic cancer, and obesity are examples of conditions for which the composition of the microbiota has been indicated to play a role.

Other microbiomes

Apart from humans, microbiomes are also found in animals and in different habitats on Earth. Animals, like humans, have microbiomes that are essential for their lives and functions. The most influential bacteria for life on Earth are found in the soil, sediments, and seas. The well-known functions of these are to provide nutrients like nitrogen and phosphorus to plants as well as to produce growth hormones. By decomposing dead organic matter, they contribute to soil structure and the cycles of nature.

Effects of Antibiotics on the Microbiome

All antibiotics affect and kill pathogens at the site of infection but also bacteria that normally live in the body. This can cause several unwanted side effects and diseases that should prevent us from taking antibiotics when not needed. For example:

Exposure to antibiotics can lead to changes and/or destabilization (dysbiosis) in the human microbiota. This can in turn lead to diseases not necessarily directly caused by a single pathogen but caused by disruption of the composition and diversity of the microbiota.

Whenever a population of bacteria is exposed to an antibiotic, any bacteria that are resistant to that antibiotic gain an advantage. As many other bacteria die, the resistant ones can increase in number. Widespread use of antibiotics thus leads to the selection of resistant bacteria that in turn may spread and cause infections that are difficult to treat.

Learn more in " Mutations and selection" and " Why should I care ".

Selected Resources

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Microbes permeate not just the entire planet but are also found in large numbers in animals and humans. The first thing to learn about bacteria is that most are beneficial and do not cause disease. In fact, they play a vital role - in the environment, animals, and humans.

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- Some are pathogens --> Causes diseases and infections
- They are able to reproduce quickly through Binary Fission --> Duplicate every time

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If learning how to grow bacteria interests you, read on.
How Can Bacteria Help Us?
How Can Bacteria Harm Us?

What Are Antibacterial Agents?
Experiment #1: Cheek Cell Swab
Experiment #2: Testing Antibacterial Agents
Experiment #3: Soap Survey
Experiment #4: Bacteria in the Air
Experiment #5: Homemade Yogurt
More Experiment Ideas
Bacteria Overview

Bacteria are one-celled, or unicellular, microorganisms. They are different from plant and animal cells because they don't have a distinct, membrane-enclosed nucleus containing genetic material. Instead, their DNA floats in a tangle inside the cell.

Individual bacteria can only be seen with a microscope, but they reproduce so rapidly that they often form colonies that we can see. Bacteria reproduce when one cell splits into two cells through a process called binary fission. Fission occurs rapidly in as little as 20 minutes. Under perfect conditions a single bacterium could grow into over one billion bacteria in only 10 hours! (It's a good thing natural conditions are rarely perfect, or the earth would be buried in bacteria!)

Growing and testing bacteria is a fun any-time project or a great science fair project. Bacteria are everywhere, and since they reproduce rapidly they are easy to study with just a few simple materials. All you need are some petri dishes, agar, and sterile swabs or an inoculating needle. Agar is a gelatinous medium that provides nutrients and a stable, controlled environment for bacteria growth. Most bacteria will grow well using nutrient agar, but some more fastidious bacteria (those with more complex nutrient requirements like Bacillus stearothermophilus, Branhamella catarrhalis, and Bacillus coagulans) prefer tryptic soy agar.
Physical methods:
You also need a source for bacteria, and this is not hard to find! You can swab your mouth or skin, pets, soil, or household surfaces like the kitchen sink or toilet bowl. If you want to study a particular type of bacteria, you can also purchase live cultures. Keep reading to see four experiments using bacteria, and many more ideas for science projects (also consider this hands-on Bacteria Growing Kit)! Adult supervision is recommended when working with bacteria.
Chemical methods:
How Can Bacteria Help Us?

Where would we be without bacteria? Well, we might not be getting bacterial diseases, but we would still be a lot worse off! Bacteria perform all sorts of very important functions, both in our bodies and in the world around us. Here are just a few.

Digestion. Our large intestines are full of beneficial bacteria that break down food that our bodies can't digest on their own. Once the bacteria break it down, our intestines are able to absorb it, giving us more nutrients from our food.

Vitamins. Bacteria in our intestines actually produce and secrete vitamins that are important for our health! For example, E. coli bacteria in our intestines are a major source of vitamin K. (Most E. coli is good for us, but there is a harmful type that causes food poisoning.)

Food. Bacteria are used to turn milk into yogurt, cheese, and other dairy products.
Preparing Culture Dishes
Oxygen. Cyanobacteria (which used to be called blue-green algae) live in water and perform photosynthesis, which results in the production of much of the oxygen we need to breathe.

Cleanup. Oil spills, sewage, industrial waste - bacteria can help us clean all of these up! They 'eat' the oil or toxins and convert them into less harmful substances.

Bacteria are amazing creatures, aren't they? They can be so dangerous and yet so important at the same time. Keep reading to see an experiment that uses good bacteria!

How Can Bacteria Harm Us?

Some types of bacteria cause disease and sickness. These kinds of bacteria are called pathogens. They reproduce very rapidly, like all bacteria. These come in many forms and can cause illnesses from an ear infection to strep throat to cholera. They can get into our bodies via our mouth and nose, or through cuts and scrapes. Some are airborne, others are found in food, resulting in food poisoning. Bacteria are also the cause of plaque buildup on our teeth, which can lead to cavities and gum disease.

Before the discovery of antibiotics, many severe bacterial diseases had no cure and usually resulted in death. Antibiotics work by destroying bacteria or inhibiting their reproduction while leaving the body's own cells unharmed. After a time, some bacteria develop resistance to an antibiotic, and it will no longer be effective against them. Because of this, scientists are always researching new antibiotics. (Many diseases, such as chicken pox, hepatitis, or polio, are caused by viruses rather than bacteria. Antibiotics have no effect against these diseases.)
Preparing Sensitivity Squares

Collecting Bacteria

Setting Up an Experiment

Bacterial infections are common, but many of them can be avoided by good cooking, cleaning, and hand-washing practices.

What Are Antibacterial Agents?

How do people stop bacteria from growing and spreading? They control it in two ways: by killing the bacteria cells, and by stopping the bacteria from reproducing. An agent is a solution or method which either kills or stops reproduction. Bactericides are agents that kill bacteria cells. Static agents inhibit cell growth and reproduction.

There are a variety of ways to kill bacteria or keep it from reproducing.

Sterilization. The application of heat to kill bacteria. Includes incineration (burning), boiling, and cooking.

Pasteurization. The use of mild heat to reduce the number of bacteria in a food.

Cold temperatures. Refrigeration and freezing are two of the most common methods used in homes, for preserving food's life span.

Antiseptics. These agents can be applied directly to living tissues, including human skin.

Disinfectants. These agents are not safe for live tissues. Disinfectants are used to clean toilets, sinks, floors, etc.

Preservatives. These are used in almost every processed food that is available today. They inhibit bacterial growth in foods.
Some food preservatives are: sodium benzoate, monosodium glutamate (MSG), sulfur dioxide, salts, sugar, and wood smoke.

Antibiotics. These kill the bacteria cells that are inside the body, without harming normal cells. Antibiotics often are able to cure once-fatal diseases, such as scarlet fever. However, they can kill good bacteria along with the bad.

Amoxycillin and Ampicillin-inhibit steps in cell wall synthesis (building)

Penicillin-inhibits steps in cell wall synthesis

Erythromycin-inhibits RNA translation for protein synthesis

SAFETY NOTE

While most environmental bacteria are not harmful to healthy individuals, once concentrated in colonies, they can be hazardous.
Materials What To Do
To minimize risk, wear disposable gloves while handling bacteria, and thoroughly wash your hands before and after. Never eat or drink during bacteria studies, nor inhale or ingest growing cultures. Work in a draft-free room and reduce airflow as much as possible. Keep petri dishes with cultured mediums closed-preferably taped shut-unless sampling or disinfecting. Even then, remove the petri dish only enough to insert your implement or cover medium with bleach or 70% isopropyl alcohol.

When finished experimenting, seal dishes in a plastic bag and dispose. Cover accidental breaks or spills with bleach or alcohol for 10 minutes, then carefully sweep up, seal in a plastic bag, and discard.

Before you can grow bacteria, you'll need to prepare sterile culture dishes. A 125ml bottle of nutrient agar contains enough to fill about 10 petri dishes.

Water Bath Method - Loosen the agar bottle cap, but do not remove it completely. Place the bottle in hot water at 170-190 °F until all of the agar is liquid. To prevent the bottle from tipping, keep the water level even with the agar level.

Let the agar cool to 110-120 °F (when the bottle still feels warm but not too hot to touch) before pouring into petri dishes.

Slide open the cover of the petri dish just enough to pour agar into the dish. Pour enough agar to cover 1/2 to 2/3 of the bottom of the dish (about 10-13ml). Don't let the bottle mouth touch the dish. Cover the dish immediately to prevent contamination and tilt it back and forth gently until the agar coats the entire bottom of the dish. (Fill as many dishes as you have agar for: you can store extras upside down until you're ready to use them.)

Let the petri dishes stand one hour for the agar to solidify before using them.

Experiment #1: Cheek Cell Swab

Make a culture dish using the instructions above. Once the culture dish is prepared, use a sterile cotton swab or inoculating needle and swab the inside of your cheek. Very gently rub the swab over the agar in a few zigzag strokes and replace the lid on the dish. You'll need to let the dish sit in a warm area for 3-7 days before bacteria growth appears. Record the growth each day with a drawing and a written description. The individual bacteria are too tiny to see without a high-power microscope, but you can see bacteria colonies. Distinguish between different types of bacteria by the color and shape of the colonies.

Experiment #2: Testing Antibacterial Agents

Each experiment should have a control dish that shows bacteria growth under normal conditions and one or more test dishes in which you change certain variables and examine the results. Examples of variables to test are temperature or the presence of antiseptics. How do these affect bacteria growth?

Label one dish 'Control.' Then in your test dish, use tweezers to add the sensitivity squares that have been soaked in a substance you wish to test for antibacterial properties. It's a good idea to add a plain square of blotter paper to see if the paper by itself has any effect on bacteria growth. For best results, use multiple test dishes and control the variables so the conditions are identical for each dish: bacteria collected from the same place, exposed to the same amount of antibacterial substance, stored at the same temperature, etc. The more tests you perform, the more data you will collect, and the more confident you can be about your conclusions.

Place all the dishes in a dark, room-temperature place like a closet.

Wait 3-7 days and examine the bacteria growth in the dishes, without removing the lids. You will see multiple round dots of growth; these are bacteria colonies. Depending on where you collected your bacteria samples, you may have several types of bacteria (and even some mold!) growing in your dishes. Different types of colonies will have different colors and textures. If you have a compound or stereo microscope, try looking at the colonies up close to see more of the differences.

Compare the amount of bacteria in the control dish to the amount in the test dishes. Next, compare the amount of bacteria growth around each paper square. Which one has bacteria growing closest to it? Which one has the least amount of bacteria growing near it? If you did more than one test dish, are the results similar in all the test dishes? If not, what variables do you think might have caused the results to be different? How does this affect your conclusions?

For a variation on this experiment, test the effect of temperature on bacterial growth instead of using sensitivity squares. Put a control dish at room temperature, and place other dishes in dark areas with different temperatures.

Experiment #3: Soap Survey

Every time you touch something you are probably picking up new bacteria and leaving some behind. This is how many infectious diseases spread - we share our bacteria with everyone around us! Even bacteria that lives safely on our skin can make us sick if it gets inside our bodies through our mouths or cuts and scrapes. This is one reason why it is so important that we wash our hands frequently and well.

What kind of soap works best for cutting down on the bacteria on our hands? You can test this by growing some bacteria cultures using agar and petri dishes.

1. Prepare the agar according to the directions on the label, then pour enough to cover the bottom of each petri dish. Cover the dishes and let them stand for about an hour until the agar has solidified again. (If you aren't going to use them right away after they have cooled, store them upside down in the refrigerator.)

2. When your petri dishes are ready, collect some bacteria from your hand or the hand of a volunteer. (Make sure the person hasn't washed his or her hands too recently!) Do this by rubbing the sterile swab over the palm in a zigzag pattern.

3. Remove the cover from the petri dish and lightly rub the swab back and forth in a zigzag pattern on the agar. Turn the dish a quarter turn and zigzag again. Cover the dish and repeat steps two and three for the other dish, using a new sterile swab. Label the dishes "Test" and "Control." (You may want to do more than one test dish, so you can compare the results.)

4. Cut the blotter paper into small "sensitivity squares." Use permanent ink to label the squares for the different types of hand cleaners you are going to test, e.g., "R" for regular soap, "A" for antibacterial soap, and "S" for hand sanitizer. Using tweezers, dip each square into the appropriate cleaner. Blot the excess cleaner on a paper towel and then place the squares on the agar in the "Test" dish. (Spread the squares out so there is distance between them.) Add one square of plain blotter paper to test if blotter paper by itself has any effect. Don't put any squares in the "Control" dish - this one will show you what the bacterial growth will look like without any soap.

5. Put the dishes in a dark, room-temperature place like a closet and leave them undisturbed for a few days.

What Happened

The rate of bacteria growth in your dishes will depend on temperature and other factors. Check your cultures after a couple of days, but you'll probably want to wait 5-7 days before recording your data. You will see multiple round dots of growth; these are bacteria colonies. There may be several types of bacteria growing in the dishes. Different types of colonies will have different colors and textures.

For each soap test, count and record the number of bacteria colonies in each dish. To see how effective each soap was, divide the number of colonies in the test dish by the number of colonies in the control dish, then subtract the result from 1 and write the answer as a percentage. For example, if your control dish had 100 colonies and your soap test dish had 30, the soap eliminated 70% of the bacteria: 1 - (30 ÷ 100) = .7 = 70%

According to your results, which type of soap was the most effective at eliminating bacteria? Does "antibacterial" soap really work better than regular soap? How well did washing hands in water without soap work? What further tests could you do to determine which soaps and hand washing methods are most effective at eliminating bacteria?

Experiment #4: Bacteria in the Air

You need two culture dishes for this experiment, in which you'll demonstrate how antibacterial agents (such as antibiotics and household cleaners) affect bacteria growth.

Leave the dishes with their lids off in a room-temperature location. Leave the culture dishes exposed for about an hour.

While you wait, cut small squares of paper (blotter paper works well), label them with the names of the antibacterials you're going to test (e.g. 'L' for Lysol, 'A' for alcohol, etc.), and soak each in a different household chemical that you wish to test for antibacterial properties. If you have time, you might also experiment with natural antibacterial agents, such as tea tree oil or red pepper. Wipe off any excess liquid and use tweezers to set each of the squares on a different spot in one of the culture dishes. The second culture dish is your 'control.' It will show you what an air bacteria culture looks like without any chemical agents.

Store the dishes (with lids on) in a dark place like a closet where they will be undisturbed for a few days. After 3-7 days, take both culture dishes and carefully observe the bacteria growth in each dish, leaving the lids on. The bacteria will be visible in small, colored clusters. Take notes of your observations and make drawings. You could also answer the following questions. In the control culture, How much of the dish is covered with bacteria? In the sensitivity square test culture, Have the bacteria covered this dish to the same extent as the control culture? What effect have each of the chemicals had on the bacteria growth? Did a particular chemical kill the bacteria or just inhibit its growth?

For further study you could use an antibiotic disc set to see what different antibiotics can do against bacteria.

For a more advanced project, learn how gram staining relates to the use of antibiotics.

Experiment #5: Homemade Yogurt

Generally when people think of 'bacteria,' they think of harmful germs. However, not all forms of bacteria are bad!
You can enjoy a tasty product of good bacteria by making a batch of yogurt at home.

You'll need to use a starter (available at grocery or health food stores), or else one cup of plain, unflavored yogurt that has live cultures in it. (If it contains live cultures, it will say so on the container.)

Slowly heat four cups of milk until it is hot, but not boiling or scalding. The temperature should be around 95-120 degrees to kill some of the harmful bacteria. Cool slightly, until milk is warm, and then add one cup of active yogurt or the starter.

Put the mixture in a large bowl (or glass jars) and cover. Make sure that the bowl or jars are sterilized before using by either running them through the dishwasher or washing them with very hot water.

There are two different methods for culturing the yogurt mixture: You can put the covered bowl or jars into a clean plastic cooler, and fill the cooler with hot water to just below the top of the culture containers. With this method, you will need to occasionally refill the cooler with hot water, so that the temperature of the yogurt stays consistent. The other method is to wrap the containers in a heating pad and towels, setting the heating pad on low to medium heat.

Check the mixture after heating for 3 1/2 to 4 hours. It should be 'set up,' having a smooth, creamy consistency similar to store-bought yogurt. If the mixture is not set up yet, heat it for another 1-2 hours. When it is the right consistency, add some flavoring-such as vanilla extract, chocolate syrup, or berries-and store the yogurt in the refrigerator. It should keep for a couple of weeks. For safety, we suggest that you do not eat any yogurt that has separated or has a non-typical consistency.

More Bacteria Experiment Ideas

Here are some other project ideas for you to try on your own or use as a basis for a bacteria science fair project:

Mouthwash. Swab your teeth and gums and see how well toothpaste or mouthwash work against the plaque-causing bacteria on your teeth.

Dog's mouth: Have you heard people say that dogs' mouths are cleaner than humans'? Design an experiment to test whether this is really true!

Band-aid. Some band-aids are advertised as being antibacterial. Test to see if they really work better than regular band-aids at inhibiting bacteria.

Water bottle. Is it safe to keep refilling a water bottle without washing it? Test a sample of water from the bottom of a water bottle that has been used for a couple days and compare it to a sample from a freshly-opened, clean water bottle. You can also test to see if a bottle gets more bacteria in it if you drink with your mouth or with a straw.

Shoes. Do bacteria grow in your shoes? Is there a difference in bacteria growth between fabric shoes and leather? Do foot powders work to cut down on bacteria?

Toothbrush. Do bacteria grow on your toothbrush? What are some ways you could try to keep it clean? Mouthwash? Hot water?

Makeup. Some people recommend getting new mascara every six weeks because bacteria can grow in the tube. Test this by comparing bacteria growth from old mascara and new, unused mascara. You can also test how much bacteria is on other kinds of makeup.

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How to Grow Bacteria: 5 Experiments to Grow & Test Bacteria

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If learning how to grow bacteria interests you, read on. How Can Bacteria Help Us? How Can Bacteria Harm Us? What Are Antibacterial Agents? Experiment #1: Cheek Cell Swab Experiment #2: Testing Antibacterial Agents Experiment #3: Soap Survey Experiment #4: Bacteria in the Air Experiment #5: Homemade Yogurt More Experiment Ideas Bacteria are one-celled, or unicellular, microorganisms. They are different from plant and animal cells because they don't have a distinct, membrane-enclosed nucleus containing genetic material.

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Introduction

Bacteria are microorganisms that grow everywhere. We can collect and grow them in specially prepared petri dishes. Blood agar or tryptic soy agar with 5% sheep's blood is an excellent medium for supplying bacteria with nutrients and an environment in which we can see them grow.

Sterile powdered agar with nutrients can be mixed with water, heated and then poured into empty petri plates or ready-to-use dishes can be purchased. The undigestible agar is a gelatin-like substance with a semi solid surface on which the bacteria can grow while they consume the added nutrients (like sheep's blood). In fact, this is why gelatin itself does not make a good growing medium. Some bacteria can digest gelatin, which is a protein derived from animal tissue. This destroys the growing surface in the petri plate making it unsuitable as a bacteria growth medium.

CAUTION. Most bacteria collected in the environment will not be harmful. However, once they multiply into millions of colonies in a petri dish they become more of a hazard. Be sure to protect open cuts with rubber gloves and never ingest or breathe in growing bacteria. Keep growing petri dishes taped closed until your experiment is done. Then you should safely destroy the fuzzy bacteria colonies using bleach.

Below are general outlines of three types of experiments involving bacteria growth. They are offered to assist in designing your own experiment or project.

Experiment 1: Direct Contact

Discussion.

In this type of experiment, bacteria is transferred directly to the prepared petri plate via direct contact. You can test the effectiveness of different soaps by treating different petri dishes with "dirty" hands before washing and "clean" hands after washing. Or, you can press a variety of common objects like coins, combs, etc. on different plates and compare the bacteria growth that results.

What you need.

Prepared petri plates containing agar medium and nutrients.
The Science Company has these available at this link.

Bacteria on hands, paws, etc.

Wax pencil for labeling dishes.

Masking tape.

Bleach.

1. Prepared petri dishes should be refrigerated until used and always stored upside down (i.e media in upper dish, cover on bottom). This keeps condensation which forms in the lid from dropping onto and disrupting the bacteria growing surface.

2. When ready to use, let dishes come to room temperature before taking samples (about one hour).

3. Without tearing the agar surface, inoculate the dish by gently pressing fingers, finger nails, coin, etc onto agar surface. (Direct contact of lips or tongue is NOT a good idea.)

4. Replace cover on dish, tape closed, and label each dish so you know the source of the bacteria. Store upside down.

5. Let grow in undisturbed warm location. Bacteria can grow at any temperature from about ambient room temperature (hopefully around 70°F) all the way up to about 100°F. Do not place in sunlight or on a heating register.

6. You should see growth within a couple of days. The dishes will start to smell which means the bacteria are growing.

7. Make observations and keep records of what you see growing in each dish. Can you make any conclusions about what objects had the most bacteria?

8. Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink. Caution - do not allow bleach to touch your skin, eyes or clothes. It will burn!

Experiment 2: Collected bacteria samples

Discussion.

Use a sterilized inoculating loop or sterile swabs to collect bacteria from different locations and then streak each petri dish with your sample. This involves a bit more technique than Experiment 1 but offers a wider choice of bacteria sampling locations. Swabs can be run over doorknobs, bathroom fixtures, animal mouths, etc.

What you need.

1. Prepared petri dishes should be refrigerated until used and always stored upside down (i.e media in upper dish, cover on bottom). This keeps condensation which forms in the lid from dropping onto and disrupting the bacteria growing surface.

2. When ready to use, let dishes come to room temperature before taking samples (about one hour).

3. Collect bacteria from each location using one swab (or resterilized innoculating loop) for each new spot.

4. Inoculate each dish by streaking a pattern gently across the entire agar surface without tearing into it. Another common technique is to divide each plate into four quadrants by marking the lid with a cross. Streak your sample in straight lines starting in quadrant 1. Generally, after a few days, quadrant one will show the most growth. Depending on bacteria abundance on the swab, quadrant 4 may show no grow or only a few colonies. It is sometimes easier to distinguish different bacteria types in this low growth, less cluttered area.

5. Replace cover on dish, tape closed, and label each dish so you know the source of the bacteria. Store upside down.

6. Let grow in undisturbed warm location, ideally in an environment around 100° F (37° C) - not in sunlight or on a heating register.

7. You should see growth within a couple of days. The dishes will start to smell which means the bacteria are growing.

8. Make observations and keep records of what you see growing in each dish. Can you make any conclusions about what locations had the most bacteria?

9. Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink. Caution - do not allow bleach to touch your skin, eyes or clothes. It will burn!

Experiment 3: Testing the effectiveness of bacteria killing agents

Discussion.

In this type of project, a petri dish is inoculated with bacteria then a paper disk (filter paper) treated with an antiseptic agent is placed in the dish. After several days, a halo develops around the paper disk indicating a zone of no growth. Comparisons can be made between different antibacterial agents.

What you need.

Prepared petri dishes containing agar medium and nutrients.
The Science Company has these available at this link.

Bacteria collected from doorknobs, bathroom fixtures, etc.

Wax pencil for labeling dishes.

Masking tape.

Sterile swabs or inoculating loop.

Alcohol burner (source of flame to sterilize inoculating loop).

Antibacterial agent (soaps, disinfectants, etc.).

Sterile water.

Test tubes, 12 x 75mm.

Filter paper or paper towel.

Small containers in which to soak paper disks.

Hole punch.

Tweezers.

Ruler.

Bleach.

1. Prepared petri dishes should be refrigerated until used and always stored upside down (i.e media in upper dish, cover on bottom). This keeps condensation which forms in the lid from dropping onto and disrupting the bacteria growing surface.

2. Prepare sterilized water by boiling water and letting cool to room temperature.

3. When ready to use, let petri dishes come to room temperature before taking samples (about one hour).

4. Prepare antiseptic disks by using a hole punch to create paper disks out of a piece of filter paper or paper towel. Soak one disk in each antibacterial agent to be tested. Set aside until step 6.

5. Collect bacteria from each location using one swab for each new spot.

6. Fill a small test tube partly full of sterilized water. Dip bacteria laden swab into water. This will transfer some of the bacteria you collected into the water. Now, inoculate a petri dish by pouring the water into the dish so the entire surface is covered. Pour out excess water. Repeat for each bacteria sample using fresh water and clean test tube each time.

7. Place a pretreated antiseptic disk in each inoculated petri dish.

8. Replace cover on dish, tape closed, store upside down. Be sure to label each petri dish with a name or number.

9. Let grow in undisturbed warm location, ideally in an environment around 100° F (37° C) - not in sunlight or on a heating register.

10. You should see growth within a couple of days. You should also see a "halo" around each disk indicating a no growth zone. Measure and compare the size of the kill zone to determine effectiveness of each antibacterial agent.

11. Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink. Caution - do not allow bleach to touch your skin, eyes or clothes. It will burn!

There are many variations of the basic steps outlined above. Let us know what you tested and how your experiment turned out. We'd be delighted to hear from you! Click here and use our Contact Us form.

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Bacteria Growing Experiments in Petri Plates

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Bacteria are microorganisms that grow everywhere. We can collect and grow them in specially prepared petri dishes. Blood agar or tryptic soy agar with 5% sheep's blood is an excellent medium for supplying bacteria with nutrients and an environment in which we can see them grow.

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Measure zone of inhibition/ Kirby Bauer test

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Measure zone of inhibition/ Kirby Bauer test

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1) Zone of inhibition
Grow petri dish of bacterias
- Put a filter paper disk infused in disinfectant into the middle of petri dish
- The disinfectant will spread through the agar through diffusion from high concentration to low concentration
- Areas where disinfectants worked will be clear as no bacteria will grow near the disinfectant--> A circle will form around the disinfectant
- Measure the area of circle to find the zone of inhibition --> Use a clear ruler to measure from the centre of disinfectant disk to the edge of area with no growth to get the radius of circle
- The larger the zone of inhibition, the more sensitive the bacteria is to that disinfectant and the smaller the zone of inhibition, the less sensitive the bacteria is to that disinfectant
- Compare the area of zone of inhibition of different disinfectants

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Bacteria are some of the most abundant organisms on Earth. Scientists estimate that there are over one trillion different species of bacteria, amounting to over five million trillion trillion (yes, that's two separate trillions) individuals on the planet.

Out of all those bacteria, though, less than 1 percent cause disease in humans. Those diseases can range from stomach upset, as you can get from a mild infection, to serious and fatal illnesses like the bubonic plague (caused by the Yersinia pestis bacteria) that killed 50 million people in the 14th century.

That's why the discovery of antibiotics, which are medications that eliminate bacteria, has saved so many lives. The trouble with bacteria is that they adapt and evolve very quickly, which leads to antibiotic-resistant strains of bacteria becoming increasingly common. Measuring the zone of inhibition for a strain of bacteria can tell scientists and physicians whether it is resistant to an antibiotic.

Antibiotics are medications that kill bacteria. They work by targeting and resulting in the death of bacterial cells while leaving your human cells alone. Each antibiotic works in a slightly different way by targeting bacteria-specific structures and signaling to eliminate them.

For example, penicillin (one of the most famous antibiotics) interferes with bacterial cell walls, which leads to them not functioning properly and, thus, dying. Medications that work like this are called beta-lactam antibiotics.

Macrolide antibiotics target bacterial ribosomes. This prevents bacteria from synthesizing proteins, which means that the bacteria cannot survive. A common example is erythromycin, an antibiotic that's used to treat a variety of infections including bronchitis and a number of skin infections.

Quinolone antibiotics are another common type of antibiotic that work by interfering with bacterial DNA.

After the initial discovery of antibiotics in the 1920s, scientists quickly realized that bacteria were evolving to be resistant to the medications. Many scientists then attempted to create methods that allowed them to test how susceptible bacterial strains were to antibiotics to understand what they were dealing with, so to speak.

The initial tests involved serial dilutions of bacterial broth spread onto plates with varying concentrations of antibiotic to determine susceptibility. This method took a long time, however.

That's where the Kirby-Bauer test comes in. This method was standardized by microbiologists W. M. M. Kirby and A. W. Bauer. Their test takes pure bacterial culture and streaks it onto an agar plate. Then, a small disk infused with antibiotics (appropriately called an antibiotic disk) is placed onto the agar plate. Various disks with different antibiotics are placed around the plate, and the bacteria are left to incubate for a certain amount of time.

Once the disk is placed onto the plate, the antibiotics will start to diffuse out. If the bacteria being studied is sensitive to the antibiotic, then no bacteria will grow close to the disk because it will be killed by the medication.

But as you move farther away from the antibiotic disk, the concentration of the antibiotic will decrease. At a certain distance from the disk, you'll start to see bacterial growth again because the antibiotic concentration is too low to affect the bacteria.

The area around the antibiotic disk that has no bacterial growth is known as the zone of inhibition. The zone of inhibition is a uniformly circular zone of no bacterial growth around the antibiotic disk. The larger this zone is, the more sensitive the bacteria is to that antibiotic. The smaller the zone is, the more resistant (and, thus, less sensitive) the bacteria is.

Besides naming this practice and protocol, scientists Kirby and Bauer also created standardized charts that used the diameter of the zone of inhibition to determine the bacteria's sensitivity or resistance to the bacteria.

These charts can be found here and use the bacterial species, the type of antibiotic used and the zone of inhibition diameter to determine whether the bacteria is resistant, intermediately sensitive or susceptible to that antibiotic.

Note: You always measure the zone of inhibition in terms of millimeters.

To measure the zone of inhibition, first place the plate on a non-reflective surface. Take a ruler or caliper that measures in millimeters and place the "0" in the center of the antibiotic disk. Measure from the center of the disk to the edge of area with zero growth. Take your measurement in millimeters.

This measures the radius of the zone of inhibition. Multiply that by two in order to get the diameter.

You can also measure directly across the zone of inhibition from edge to edge crossing through the center of the antibiotic disk to directly measure the diameter instead of measuring the radius.

About the Author

Elliot Walsh holds a B.S in Cell and Developmental Biology and a B.A in English Literature from the University of Rochester. He's worked in multiple academic research labs, at a pharmaceutical company, as a TA for chemistry, and as a tutor in STEM subjects. He's currently working full-time as a content writer and editor.

Photo Credits

hisartwork/iStock/Getty Images

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The discovery of antibiotics has saved so many lives. The trouble with bacteria is that they adapt and evolve very quickly, which leads to antibiotic-resistant strains of bacteria. Measuring the zone of inhibition for a strain of bacteria can tell scientists whether it is resistant to an antibiotic.

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Using a calorimeter
- As the number of bacterial cells increase, the % of transmission will decrease

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Loreto Sixth Form College A level Biology

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Estimating the growth of bacteria is extremely important. Environmental health officers regularly inspect food premises and take sample for analysis. Water boards check water supplies daily. Many products are produced using bacteria grown in fermenters. Measuring their growth is an important part of the process.

There are several different methods of measuring growth:

* Rough estimates of growth rates can be made by regularly measuring the diameter of a bacterial or fungal colony as it spreads from a central point to cover the surface of a

* The size of a population of microorganisms in liquid culture may be measured by counting cells directly or by first diluting the original sample and then counting cell numbers (see below), or by taking some indirect method such as the turbidity (cloudiness) of the culture.

Direct cell counts may be divided into:

1. Total counts = which include both living cells and dead cells
2. Viable counts = which count living cells only

In practice, it is never possible to count whole populations of microorganisms. Instead, the cells in a very small sample of culture are counted, and the result multiplied up to give a population density in organisms per cm3 of culture . Even then, the population density is likely to be so high that are usually made in known dilutions of the culture , usually in 10-fold steps . This is known as

The dilution plating technique is as follows:

A culture medium, such as milk or a water sample, is made into a series of dilutions using the serial dilution technique.

of each of the 1cm (the same as saying 1ml) diluted samples (see diagram above), are individually streaked onto sterile agar plates, which are then placed in an incubator at 25oC for two days to allow time for the bacteria to grow. After all the streaks have been allowed to grow, the dilution at which the colonies are distinct and separate is noted down (this might be the 1/1000 dilution from the example above). If the dilution is insufficient then colonies will merge, referred to as 'clumping', and counting is inaccurate (the example above would be the 1/10 and the 1/100 dilution). The distinct and separate colonies of bacteria from the agar plate you have chosen are counted with the assumption being made that each colony has arisen from a single cell, which has divided asexually, from the original culture medium. To find the total viable cell count the number of colonies you count is multiplied by the appropriate dilution factor. So in the example above this would be:

159 colonies counted on the 1/1000 dilution agar plate
So 159 x 1000 = 1.59 x 10 to the power 5 bacteria in the original sample.

However, if the dilution is insufficient then colonies will merge (see 1/10 and 1/100 dilution agar plates above), referred to as 'clumping', and counting is inaccurate, resulting in an underestimate of numbers

Using a Haemocytometer

A more accurate method involves using a haemocytometer. This is a specialised microscope slide originally used to count red blood cells. Using the haemocytometer gives total cell counts as it is not possible to distinguish between living and dead cells (you are not required to describe or use a haemocytometer.)

Using Turbidimetry

A third method, known as turbidimetry, involves using a colorimeter to measure the cloudiness or turbidity of the culture as cell numbers increase. Results are derived by comparison with a standard graph of light absorbance plotted against known cell numbers (You are not required to describe or use a calorimeter).

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Estimating the growth of bacteria is extremely important. Environmental health officers regularly inspect food premises and take sample for analysis. Water boards check water supplies daily. Many products are produced using bacteria grown in fermenters. Measuring their growth is an important part of the process.

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In the early stages of working with mushrooms, the environment needs to be as sterile as possible. In the early stages of growth, mushrooms cannot compete with the growth of molds and bacteria and will be over run.

Preparing your Potato Dextrose Agar (PDA)
For every 1 Liter of Agar Final Mixed Solution you will need the following.

20 grams Bacteriological Agar

200g Potatoe infusion

4 g of Yeast Extract

20 g Dextrose

1 Liter of Distilled Water

Autoclave or Pressure Vessel

Method:

1. Place your pre cleaned flask on a kitchen scale. Make sure your scale now reads Zero. Add your dry ingredients first.

2. Now add potatoe infusion until the scale reads 250 grams.

3. Pick up the flask and swirl the solution until no dry matter can be seen and most of the agar has been dissolved.

4. Return the flask to your scale and add water until your reach 500 grams. Again swirl the solution.

5. Return the flask and add water until you read 1000 grams. Again swirl the solution.

6. Cut a piece of tin foil - 300 mm by 80 mm. Roll up a piece of kitchen towel into a tight roll.Now, half way sticking over the mouth of the Erlenmeyer flask, wrap your tin foil in a tube around the glass. Place the rolled up kitchen towel in the tube and fold over the mouth of the flask to hold the paper. (This acts as a filter when autoclaving your solution. As pressure drops in your pressure vessel, the flask will balance air pressure and suck in air, for this reason we need a filter.)

7. Pressures sterilize the Agar solution for 45 minutes.

8. Open the pressure vessel, once cooled, in front of a flow hood or in a cleaned environment (glove-box).

9. Pour your agar into petri dishes (90mm) or small glass jars for use, do this rhythmically and do not linger. From 1 liter of Agar you can make 35 - 40 dishes.

10. After pouring and cooling your agar dishes, keep them in a big zip lock bag, to ensure they do not contaminate. You can keep these in the fridge for 28 days.

Prepare potato infusion:

Wash two medium sized potatos (200g) and cut them into 2.5cm cubes and place in a clean pot and add 1.25 liters of CLEAN water. Bring to boil and keep the simmering temperature for 10 - 15 minutes. At this time remove the pot from the stove and allow to cool down for 5 minutes. Strain the water away from the potatos (use a fine sieve or french press) and use this water to prepare your potato infusion.

(PDA) Agar is made and then poured into petri dishes and then sterilized. The petri dishes are then moved into a clean room that contains a glove box. Cultures are taken from the mushroom and placed onto the agar in the petri dish.

Sampling a mushroom:

With clean fingers, in a clean space or glove box, split the mushroom down the middle. You will notice clean white mycelium on the inside of the mushroom that has never been exposed to air or the environment. Using a cleaned scalpel cut a piece of this mycelium and place in your readied container.

When significant growth has occurred on the agar, the agar is cut and placed in either grain to make grain spawn, nutrified liquid to make liquid culture or expanded onto more petri dishes.

Liquid culture and grain spawn can either be expanded or used to inoculate a substrate such as coffee or sawdust.

The substrate is then incubated usually in the dark under controlled climatic conditions. This can be done in a home made incubator or a room that has climate control.

Once the substrate has been fully colonised and consolidated it is moved into fruiting conditions. The fruiting conditions make the mushroom mycelium think it is under stress and dying so it sends its reproductive organs out to reproduce we call this it's called fruit.
Making Potato Dextrose Agar Petri Dishes for Mushroom Cultivation Learn to grow mushrooms! Being able to do agar work is an essential skill for the cultivator. It allows you to propagate cultures, maintain a culture library and store cultures for the long term.
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Potato Dextrose Agar (PDA) - The Educators

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In the early stages of working with mushrooms, the environment needs to be as sterile as possible. In the early stages of growth, mushrooms cannot compete with the growth of molds and bacteria and will be over run. For every 1 Liter of Agar Final Mixed Solution you will need the following.

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- Lactobacillus is one of the most common bacteria classified as a probiotic
- "Probiotic" promotes the growth of 'good' bacteria through fermented food e.g yoghurt
- Most yoghurts contain probiotics

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Eating yogurt is a simple way to add calcium and protein to your day. It's also a great grab-and-go snack for when you need a quick pick-me-up. While the dietary benefits are plentiful, yogurt with Lactobacillus, which is one of the most commonly used probiotics, may also boost your overall health.

The genus Lactobacillus is one of the most common bacteria classified as a probiotic, according to Harvard Health Publications. Probiotics promote the growth of "good" bacteria through fermented foods like yogurt and over-the-counter supplements.

And when good bacteria or live cultures are present, the Academy of Nutrition and Dietetics says their presence may change or repopulate intestinal bacteria to balance gut flora. Which is great news since this also creates an environment not suitable for harmful bacteria. Basically, what all of this means is that probiotics may have a positive impact on your overall health, especially gastrointestinal health.

More specifically, the Academy points to the role probiotics play in managing the symptoms of irritable bowel syndrome. Additionally, the National Center for Complementary and Integrative Health (NCCIH) points out that probiotics show promise in preventing antibiotic-associated diarrhea and induction or maintenance of remission in ulcerative colitis.

However, the NCCIH does stress that in general, researchers still don't know which probiotics are helpful and which are not. Plus, it's still not known how much you would need to take in a supplement or consume from foods in order to get the most health benefits. But the good news is, probiotics are safe, particularly in healthy people.

In general, most yogurts contain probiotics, but if you want yogurt with acidophilus, the National Yogurt Association's (NYA) website AboutYogurt.com, recommends looking for their "Live and Active Cultures" seal. Buying a yogurt with Lactobacillus and the NYA seal ensures that you will be eating refrigerated yogurt that contains at least 100 million cultures per gram at the time of manufacture or frozen yogurt that has 10 million cultures per gram.

With that in mind, when looking for a high-quality yogurt with acidophilus or live and active cultures, the first step is to check for the NYA seal or the words "live and active cultures" on the label. There are several brands that meet the NYA criteria, which means, you should be able to find one that you like.

Before you grab a spoon and dig in, you'll want to check the sugar and protein content. When choosing a yogurt, Harvard Health Publishing recommends sticking with one that has less than 10 grams of sugar per serving.

Additionally, you'll want to check the label for protein and go with one that has 5 grams or more of protein per serving. Many yogurt companies now offer Greek-style yogurt, which is a great choice if you want some extra protein.

When it comes to shopping for yogurt with Lactobacillus, the number of products to choose from is extensive. However, some brands including, FAGE, Chobani, Stonyfield, Yoplait and Siggi's seem to be more popular than others. Dannon yogurt probiotics vary, so it's best to check each label. They carry Dannon traditional yogurt and Dannon Activia Probiotic Yogurt.

FAGE Yogurt. FAGE Total Plain Yogurt in 0%, 2% and 5% fat and FAGE TruBlend are Greek-style yogurts that contain L. acidophilus and four additional live and active bacterial cultures including S_. thermophilus_, Bifidus, L. bulgaricus and L. casei.

Chobani Yogurt. All Chobani Greek Yogurts include the active cultures L. acidophilus, S. thermophilus, L. bulgaricus, Bifidus and L. casei on their ingredient lists. Some varieties include additional probiotics such as L. rhamnosus.

Stonyfield Organic Yogurt. All Stonyfield Organic Yogurts contain L. acidophilus, S. thermophilus, L. bulgaricus, Bifidus, L. paracasei and L. rhamnosus.

Yoplait Yogurt. Both Yoplait Original and Yoplait Light have L. acidophilus, L. bulgaricus and S. thermophilus.

Siggi's Icelandic Skyr Yogurt. The simple ingredients and low sugar make Siggi's yogurt a great choice. The live active cultures include L. acidophilus, S. thermophilus, L. delbrueckii subsp. bulgaricus, B. lactis and L. delbrueckii subsp. lactis.

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Yogurts That Contain Lactobacillus Acidophilus | Livestrong.com

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Eating yogurt is a simple way to add calcium and protein to your day. It's also a great grab-and-go snack for when you need a quick pick-me-up. While the dietary benefits are plentiful, yogurt with Lactobacillus, which is one of the most commonly used probiotics, may also boost your overall health.

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How does disinfectant inhibit bacterial growth? 

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How does disinfectant inhibit bacterial growth? 

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- Disinfectants destroy the cell wall of bacteria and interfere with their metabolism
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Considerations in Microbial Control

Controlling microbial growth is important in many fields but the degree of acceptable microbial levels can be quite different.

Learning Objectives

Discover considerations in microbial control

Key Takeaways

Key Points

Controlling microbial growth is important in the medical field, pharmaceutical and biotechnology industries, academic research, and food industry.

The degree of acceptable microbial presence can differ based on the circumstances. Sterilization as a definition means that all life was terminated, whereas sanitization and disinfection terminates selectively and partially.

Chemical agents that can eliminate or suppress microbial life are separated in different groups based on their use. The major groups are disinfectants, antiseptics, and antibiotics.

Antibacterials are divided into two broad groups according to their biological effect on microorganisms: bactericidal agents kill bacteria, and bacteriostatic agents slow down or stall bacterial growth.

Key Terms

sterilization: Any process that eliminates or kills all forms of microbial life present on a surface, solution, or solid compound.

microbicides: Compounds or substances whose purpose is to reduce the infectivity of microbes, such as viruses or bacteria.

parenteral: Administered by some means other than oral intake, particularly intravenously or by injection.

Considerations in Microbial Control

Ever since microbes were shown to cause diseases, people have invented different techniques to control their spread. Controlling microbial growth is important in the medical field, pharmaceutical and biotechnology industries, academic research, and food industry. Each antimicrobial substance or agent achieves a different level of microbial elimination by a certain mechanism.

TYPES OF MICROBIAL CONTROL

Sterilization (or sterilisation ) is a term referring to any process that eliminates (removes) or kills all forms of microbial life, including transmissible agents (such as fungi, bacteria, viruses, and spore forms) present on a surface, contained in a fluid, in medication, or in a compound. Sterilization can be achieved by applying the proper combinations of heat, chemicals, irradiation, high pressure, and filtration.

Chemical agents that can eliminate or suppress microbial life are separated in different groups based on their use.

Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on them. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores, so it is less effective than sterilisation. Disinfectants are different from other antimicrobial agents such as antibiotics, which destroy microorganisms within the body. Disinfectants are also different from biocides, as these are intended to destroy all forms of life, not just microorganisms. Disinfectants work by destroying the cell wall of microbes or interfering with their metabolism.

Antiseptics are antimicrobial substances that are applied to living tissue or skin to reduce the possibility of infection, sepsis, or putrefaction. Antiseptics are generally distinguished from antibiotics by the latter's ability to be transported through the lymphatic system to destroy bacteria within the body, and from disinfectants, which destroy microorganisms found on non-living objects.

The term antibiotic was first used in 1942 by Selman Waksman and his collaborators in journal articles to describe any substance produced by a microorganism that is antagonistic to the growth of other microorganisms in high dilution. This definition excluded substances that kill bacteria, but are not produced by microorganisms (such as gastric juices and hydrogen peroxide). It also excluded synthetic antibacterial compounds such as the sulfonamides. With advances in medicinal chemistry, most of today's antibacterials chemically are semisynthetic modifications of various natural compounds.

Many antibacterial compounds are classified on the basis of chemical or biosynthetic origin into natural, semisynthetic, and synthetic. Another classification system is based on biological activity. In this classification, antibacterials are divided into two broad groups according to their biological effect on microorganisms: bactericidal agents kill bacteria, andbacteriostatic agents slow down or stall bacterial growth.

Microbicides which destroy virus particles are called viricides or antivirals.

LEVEL OF MICROBIAL PRESENCE

The degree of acceptable microbial presence can differ based on the circumstances. Sterilization as a definition means that all life was terminated, whereas sanitization and disinfection terminates selectively and partially. Both sanitization and disinfection reduce the number of targeted pathogenic organisms to what are considered "acceptable" levels - levels that a reasonably healthy, intact body can deal with.

In general, surgical instruments and medications that enter an already aseptic part of the body (such as the bloodstream, or penetrate the skin) must be sterilized to a high sterility assurance level (SAL). Examples of such instruments include scalpels, hypodermic needles, and artificial pacemakers. For example, medical device manufacturers design their sterilization processes for an extremely low SAL. Their "one in a million" devices should be nonsterile.

This is also essential in the manufacture of parenteral pharmaceuticals. Preparation of injectable medications and intravenous solutions for fluid replacement therapy requires not only a high sterility assurance level, but also well-designed containers to prevent entry of adventitious agents after the initial product sterilization.

Food preservation is another field where the presence of microorganisms is taken under consideration. The process usually involves preventing the growth of bacteria, fungi (such as yeasts), and other microorganisms (although some methods work by introducing benign bacteria or fungi to the food).

Rate of Microbial Death

The rate of microbial death is used to develop standard protocols for sterilization in many industries.

Learning Objectives

Describe microbial death rates

Key Takeaways

Key Points

When researching microbial death rate, the goal is usually to find out the minimum time needed to achieve acceptable level of sterilization for a specific purpose.

Bacterial reduction is determined by a D-value, meaning how long it would take to reduce the bacterial population by 90% or one log10 at a given state of the killing agent.

Microbial death curves have been developed for many agents and are used in numerous industries.

Key Terms

D-value: The time needed to reduce the bacterial population by 90% or one log10 at a given temperature.

12-D reduction: The time needed to reduce the amount of bacteria by 1012 bacteria per gram or milliliter.

The rate of microbial death can be determined. It is important in order to develop standard protocols for disinfection which will facilitate the sterilization routine in many industries. The goal is to find out what is the minimum time needed to achieve acceptable level of sterilization for a specific purpose. The killing agent can be different (e.g., heat, chemical with certain concentration) depending on the specific application.

When the killing factor is heat, the phrase thermal death can be used. Thermal death time is a concept used to determine how long it takes to kill a specific bacteria at a specific temperature. It was originally developed for food canning and has found applications in cosmetics, and in producing salmonella-free feeds for animals (e.g. poultry, and pharmaceuticals).

In the food industry, it is important to reduce the amount of microbes in products to ensure proper food safety. This is usually done by thermal processing and finding ways to reduce the number of bacteria in the product. Time-temperature measurements of bacterial reduction is determined by a D-value, meaning how long it would take to reduce the bacterial population by 90% or one log ₁₀ at a given temperature. This D-value reference (D R) point is 121°C.

Z or z-value is used to determine the time values with different D-values at different temperatures with its equation shown below:

[latex]z=\frac { { T }_{ 2 }-{ T }_{ 1 } }{ { { \log{D} }_{ 1 } }-{ \log{D} }_{ 2 } }[/latex]

where T is temperature in °C. Such death curves can be empirically established for all bactericidal agents. This D-value is affected by pH of the product where low pH has faster D values on various foods. The D-value at an unknown temperature can be calculated knowing the D-value at a given temperature provided the Z-value is known. The target of reduction in canning is the 12-D reduction of Clostridium botulinum, which means that processing time will reduce the amount of this bacteria by 10 ¹² bacteria per gram or milliliter. The D R for C. botulinum is 12.6 seconds. A 12-D reduction will take 151 seconds.

Relative Resistance of Microbes

Different microbial structures and types of microbial cells have different level of resistance to antimicrobial agents.

Learning Objectives

Contrast the relative resistance of microbes

Key Takeaways

Key Points

Endospores are considered the most resistant structure of microbes. They are resistant to most agents that would normally kill the vegetative cells they formed from.

Mycobacterial infections are notoriously difficult to treat. Protozoa cysts are quite hard to eliminate too. Gram negative species have high levels of natural antibiotic resistance. Staphylococcus aureus is one of the major resistant human pathogens.

Fungal cells as well as spores are more susceptible to treatments. Vegetative bacterial and yeasts cells are some of the easiest to eliminate with different treatment methods. Viruses, especially enveloped ones, are relatively easy to treat successfully with chemicals due to the presence of lipids.

Key Terms

horizontal gene transfer: The transfer of genetic material from one organism to another one that is not its offspring; especially common among bacteria.

endospores: An endospore is a dormant, tough, and non-reproductive structure produced by certain bacteria from the Firmicute phylum.

Different microbial structures and types of microbial cells have different level of resistance to antimicrobial agents used to eliminate them.

Endospores are considered the most resistant structure of microbes. They are resistant to most agents that would normally kill the vegetative cells from which they formed. Nearly all household cleaning products, alcohols, quaternary ammonium compounds and detergents have little effect. However, alkylating agents (e.g. ethylene oxide), and 10% bleach are effective against endospores. Endospores are able to survive boiling at 100°C for hours. Prolonged exposure to ionizing radiation, such as x-rays and gamma rays, will also kill most endospores.

Certain bacterial species are more resistant to treatment than others. Mycobacterial infections are notoriously difficult to treat. The organisms are hardy due to their cell wall, which is neither truly Gram negative nor positive. In addition, they are naturally resistant to a number of antibiotics that disrupt cell-wall biosynthesis, such as penicillin. Due to their unique cell wall, they can survive long exposure to acids, alkalis, detergents, oxidative bursts, lysis by complement, and many antibiotics. Most mycobacteria are susceptible to the antibiotics clarithromycin and rifamycin, but antibiotic-resistant strains have emerged.

Protozoa cysts are quite hard to eliminate too. As cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures or harmful chemicals, or long periods without access to nutrients, water, or oxygen for a period of time. Being a cyst enables parasitic species to survive outside of a host, and allows their transmission from one host to another. Protozoa cells are also hardy to eliminate.

Gram-negative bacteria have high natural resistance to some antibiotics. Examples include Pseudomonas spp. which are naturally resistant to penicillin and the majority of related beta-lactam antibiotics. This ability to thrive in harsh conditions is a result of their hardy cell wall that contains porins. Their resistance to most antibiotics is attributed to efflux pumps, which pump out some antibiotics before the antibiotics are able to act.

Staphylococcus aureus is one of the major resistant pathogens. Found on the mucous membranes and the human skin of around a third of the population, it is extremely adaptable to antibiotic pressure. It was one of the earlier bacteria in which penicillin resistance was found-in 1947, just four years after the drug started being mass-produced. Methicillin-resistant Staphylococcus aureus (MRSA) was first detected in Britain in 1961, and is now "quite common" in hospitals. A recent study demonstrated that the extent of horizontal gene transfer among Staphylococcus is much greater than previously expected-and encompasses genes with functions beyond antibiotic resistance and virulence, and beyond genes residing within the mobile genetic elements.

Fungal cells as well as spores are more susceptible to treatments. Vegetative bacterial and yeasts cells are some of the easiest to eliminate with numerous agents and methods. Viruses, especially enveloped ones, are relatively easy to treat successfully with chemicals due to the presence of lipids.

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Controlling microbial growth is important in many fields but the degree of acceptable microbial levels can be quite different. Discover considerations in microbial control Key Points Controlling microbial growth is important in the medical field, pharmaceutical and biotechnology industries, academic research, and food industry. The degree of acceptable microbial presence can differ based on the circumstances.

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- Bacteria is transmitted the same way as viruses
- This is through air for example a person with the infection could spread it through coughing and sneezing
- It can also be spread through contact, by touching or shaking hands with an infected person

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When you get ill, you will probably know that it's usually something to do with bacteria or a virus and infection. But what most people don't realise is that a viral infection differs from a bacterial one - and the treatment varies too.

So, what is the difference between viral and bacteria infections, how are they spread and how should you treat each type of infection to ensure the speediest recovery? We have the answers:

What are viruses?

Viruses are too small to be seen by the naked eye. They can't multiply on their own, so they have to invade a 'host' cell and take over its machinery in order to be able to make more virus particles.

Viruses consist of genetic materials (DNA or RNA) surrounded by a protective coat of protein. They are capable of latching onto cells and getting inside them. The cells of the mucous membranes, such as those lining the respiratory passages that we breathe through, are particularly open to virus attacks because they are not covered by protective skin.

What are bacterial infections?

Bacteria are organisms made up of just one cell. They are capable of multiplying by themselves, as they have the power to divide. Their shapes vary, and doctors use these characteristics to separate them into groups.

Bacteria exist everywhere, inside and on our bodies. Most of them are completely harmless and some of them are very useful.

Bacteria are capable of multiplying by themselves, as they have the power to divide.

But some bacteria can cause diseases, either because they end up in the wrong place in the body or simply because they are 'designed' to invade us.

How are infections spread?

Viral and bacterial infections are both spread in basically the same ways. A person with a cold can spread the infection by coughing and/or sneezing. Bacteria or viruses can be passed on by touching or shaking hands with another person.

Touching food with dirty hands will also allow viruses or bacteria from the intestine to spread.

Bacteria or viruses can be passed on by touching or shaking hands with another person.

Body fluids, such as blood, saliva and semen, can contain the infecting organisms and transmission of such fluids, for example by injection or sexual contact, is important, particularly for viral infections like hepatitis or AIDS.

How to avoid infection

To prevent the spread of infection from both viral and bacterial infection, try the following tips:

* Wash your hands

Wash your hands thoroughly, as this is often one of the best ways to avoid catching an infection.

* Try not to touch your face

Shaking hands with someone who has a cold is risky, so avoid rubbing your eyes or nose afterwards.

* Be mindful in the kitchen

Food should be cooked or cooled down as quickly as possible.

* Store your meat and veg separately

Vegetables and meat must be stored separately and prepared on separate chopping boards.

* Opt for well-cooked meat

Meat should preferably be served well-done.

* Don't trust your sense of smell

Remember that food with these invisible organisms does not necessarily smell bad. Some organisms are killed as the food is cooked, but they can still leave toxic substances that may cause diarrhoea and vomiting.

* Practise safe sex

The use of condoms during sexual intercourse reduces the likelihood of spreading sexually transmitted infections.

How are bacterial infections treated?

Bacterial infections are usually treated with a specific antibiotic, which only kills the bacterium that has caused the disease.

To make sure that you get the right treatment, your doctor may take a sample, for example a swab from the throat or a urine sample. The microbiology laboratory will then identify the bacteria in the sample and determine which antibiotic is appropriate.

How are viral infections treated?

Viruses can't multiply until they are inside the body's cells. This is the reason why the treatment of viral infections is usually left up to the patient's own immune system, although it may be hard to accept when the doctor says the only cure is for 'nature to take its course'.

The treatment of viral infections, such as influenza, will usually involve the following:

✔️ Drinking plenty of water.

✔️ Staying at home. People who go to work or school in this condition not only risk spreading the virus to their colleagues but also run a higher risk of catching a bacterial infection.

✔️ Taking a painkiller, such as paracetamol (eg Panadol) or ibuprofen (eg Nurofen), to bring your temperature down.

✔️ With vaccines which have been developed against most viral diseases. The vaccine gives the body some help in quickly and effectively fighting the virus.

An increasing number of antiviral remedies are being developed that prevent the virus multiplying and cause the illness to run its course more quickly. Unfortunately, these remedies can still only be used on very few viruses and are of limited effectiveness.

⚠️ Antibiotics have no effect upon viral infections such as colds and flu, and it's important that we limit antibiotic use only to bacterial infections that won't get better on their own. Over-use of antibiotics reduces their effectiveness by encouraging the growth of antibiotic-resistant bacteria, which is a serious and increasing problem globally.

Last updated: 16-10-19

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How to treat viral and bacterial infections

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When you get ill, you will probably know that it's usually something to do with bacteria or a virus and infection. But what most people don't realise is that a viral infection differs from a bacterial one - and the treatment varies too.

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Your Microbial Friends [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2014 [cited 2020 Aug 11] Available from https://learn.genetics.utah.edu/content/microbiome/friends/

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- Many yoghurts contain different types of bacteria and not just one for example, they contain L. Acidophilus but also a lot of other bacteria.
- Will this affect the fairness of my results? Can I grow many different bacterias?

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Lactobacillus is a genus of beneficial bacteria. They are found pretty much everywhere and there are even some inside your digestive system right now! In fact, Lactobacillus bacteria are in many probiotic supplements and Lactobacillus species play an important role in the production of many common foods. In the garden, Lactobacillus serum can be used as a digester, helping break down organic matter and turn it into a form that is available to your plants. Since Lactobacillus bacteria are everywhere, its easy to make a concentrated culture you can use around your home and garden, and all you need is a few basic ingredients you probably already have in your kitchen. I originally saw this recipe at www.theunconventionalfarmer.com and have since come across a few similar recipes on other sites. Its good stuff and its easy to make!
The water will get cloudy as it picks up starches from the rice. Remove the rice and cook it for dinner or throw it into your compost pile. Rinse a cup or so of rice in a few cups of water. What we are after is the starchy water.

Take your dish of starchy water and find a safe place you can leave it for 3-7 days. I suggest somewhere warm and out of the way so it doesn't get spilled or disturbed. I usually keep mine in the kitchen on top of the fridge, since its slightly warm and will stay undisturbed. Bacteria from the environment will be attracted to the starchy water and will colonize the liquid in your dish.
After a few days, the liquid will start to separate into three distinct layers: Loosely covered rice wash collecting bacteria on my dirty counter.

Top- floating solids and maybe a little mold or funky stuff growing.

Middle- Cloudy liquid full of native bacteria, including Lactobacillus

Bottom- Sinking solids, rice bits, etc.

The middle layer is what we are after, so separate it from the rest and move it to a larger jar or container. The easiest way is to use your turkey baster to suck it up and transfer it to a jar. If you don't have a baster, you can skim the top layer off and carefully pour the middle layer into a new container. However you do it, try to isolate the middle layer. It doesn't have to be perfect, so just do your best to separate the middle layer without taking too much of the top or bottom layers.
Native Bacteria cultures ready to add milk. In a large jar or container, combine about 10 parts milk to 1 part of your native bacteria culture from step one.
Step 2: Add milk so the Lactobacillus takes over the culture-

So now that we have our culture containing a diverse group of native bacteria, its time to separate out the Lactobacillius. As you may have guessed, Lactobacillus LOVE milk, specifically the sugar lactose. By adding lots of milk to our collection of wild bacteria, we will encourage the Lactobacillus to take over and dominate the culture. Before long they will take it over completely, and we will be left with only the Lactobacillus we are after.

So for every 100 mL of culture from step one, you will need about one liter of milk.

Measurements don't need to be exact, but make sure to leave a few inches of room at the top of your container. Loosely cover it, but don't seal it completely air tight. We are trying to keep outside air from getting in, but still want the container to be able to vent excess gas if it needs to. You could also use an airlock lid on your container like I am doing.

Leave it undisturbed for 5-10 days at room temperature.
It will also start to smell like stinky cheese . Usually the smell stays mostly in the container, but be aware this process does create some cheesy odor that you may find unpleasant.
After a few days, the bacteria + milk mixture will start to separate into layers.

At the top, a cheesy layer will form, and the bottom will be a cloudy liquid, usually cloudy white with a little yellow tint to it.
Day 1- Milk and native bacteria culture combined. The purple and blue thingies are "Pickle Pipe" one way valves that allow the jars to vent air out but not in. They are nice tools to have when making this sort of thing, but not required. Day 7- Separation Complete Strainer lid- very useful but optional. Available most places that sell canning jars. Cheese chunk and lacto culture after separating with strainer lid Step 3: Add sugar to the lactobacillus culture to preserve and stabilize it. Mix your lacto culture with a roughly equal amount of sugar or molasses. So if you have 1 liter of lacto culture, add about 1 liter of molasses or 1 kilogram (about 2.2lbs) of sugar.
We are after the liquid layer, but the cheese layer is full of beneficial bacteria as well. It makes a great addition to your compost pile or soil. I've read you could also probably eat it or feed it to your animals, (its basically cheese and beneficial bacteria) but it smells pretty weird so I have yet to try it myself. It usually goes in my compost pile.
Finished Lacto cultures. Color may vary based on the type of sugar you use.
After about 5-10 days, the mix should be completely separated into a solid layer and a liquid layer. Use your turkey baster, strainer, or careful pouring to separate the liquid into a different jar or container. This liquid layer is full of the Lactobacillus we are after.

In order to stay alive and happy in their jar, your Lactobacilli need a long term food source. Adding a bunch of sugar or molasses gives them something to snack on and will preserve your Lacto culture for a year or more. The type of sugar doesn't seem to matter too much, but I prefer organic cane sugar as its not bleached or as heavily processed as other varieties. The type of sugar you use may effect the color of your final product, but I've made many batches with several different types of sugar and they all seemed to work fine. The finished liquid is ready to use and stable to store at room temp for at least a year, and probably much longer.

How to use your finished Lacto culture

Water it in- 15 to 30 mL per gal - Helps break down organic mater and fertilizers into plant available forms. Helps with nutrient uptake and availability. Its pretty much just beneficial bacteria and some residual sugar, so its compatible to mix in with whatever else you are watering.

Natural antifungal, Helps prevent powdery mildew. Populates plant surfaces with beneficial lactobacillus which outcompete other harmful microorganisms. Use it alone or as part of your regular IPM spray.

Make fertilizer with it- Lactobacillus will attempt to break down any organic composting material it comes into contact with. You can make "fermented plant extract" by mixing nutrient rich plant mater with lactobacillus and allowing it to break down and ferment for a few weeks. After the mix is fermented, the chunks are strained out and the remaining liquid is a very effective fertilizer containing lots of nutrients and beneficial lacto bacteria. This is a bigger topic I will cover in detail another time, but if you are interested in learning more, search the internet for "fermented plant extracts" and "dynamic accumulators" for tons more info.

Use to aid in composting or make bokashi - Water it into your compost pile. Helps break down organic matter and accelerate the composting process. Also helps reduce compost related odors. Can be used to make bokashi bran or used in anaerobic composting methods. Also seems to speed up the "cooking" process when preparing freshly mixed soil for use.
Its useful pretty much anytime you've got something organic you need to break down or deodorize!
Drain digester/deodorizer- Helps break down organic sludge stuck in your plumbing. Works well to help unclog slow drains. Pour a little bit of undiluted lacto down your drain to help break up a clog or use it diluted to help deodorize a smelly drain. Works best when you pour a little in and let it sit over night before using the drain again.

Dilute to around 15 mL per liter of water to make a deodorizing spray. Use to get rid of bad odors around the house. Very useful if you have pets or other animal related odors to deal with. Very effective deodorizer, even when heavily diluted. Effective for use on animal bedding, livestock areas etc.
Thanks for reading! I hope you learned something!

If you have any questions please don't hesitate to ask in the comments. I'll do my best to check in and answer what I can.
http://theunconventionalfarmer.com/recipes/lactobacillus-serum/ http://www.ctahr.hawaii.edu/oc/freepubs/pdf/SA-8.pdf http://waytogrow.net/diy-bokashi-composting/ A different batch of lacto. Cheesing up nicely
Nettle and Comfrey fermented plant extracts
Fermenting fan leaf FPE. 4 weeks later. Lacto is breaking them down. The liquid will be strained out and fed to plants . I water my soil with lacto and recharge before while its cooking. Its ALIVE!!!! 😛

I leave you with a few fun lacto pics from times I've used it in my garden. I will cover using lacto to make fermented plant extract (FPE) in a future article. Hopefully this serves to show you the possibilities or gets you thinking of ways you could put lacto to work in your own garden.

Sources and Recommended Reading:

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How to Make and Use Your Own Lactobacillus Culture - Dude Grows

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Hey DGC! Lactobacillus is a genus of beneficial bacteria. They are found pretty much everywhere and there are even some inside your digestive system right now! In fact, Lactobacillus bacteria are in many probiotic supplements and Lactobacillus species play an important role in the production of many common foods.

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In addition to physical methods of microbial control, chemicals are also used to control microbial growth. A wide variety of chemicals can be used as disinfectants or antiseptics. When choosing which to use, it is important to consider the type of microbe targeted; how clean the item needs to be; the disinfectant's effect on the item's integrity; its safety to animals, humans, and the environment; its expense; and its ease of use. This section describes the variety of chemicals used as disinfectants and antiseptics, including their mechanisms of action and common uses.

Phenolics

In the 1800s, scientists began experimenting with a variety of chemicals for disinfection. In the 1860s, British surgeon Joseph Lister (1827-1912) began using carbolic acid, known as phenol, as a disinfectant for the treatment of surgical wounds (see Foundations of Modern Cell Theory). In 1879, Lister's work inspired the American chemist Joseph Lawrence (1836-1909) to develop Listerine, an alcohol-based mixture of several related compounds that is still used today as an oral antiseptic. Today, carbolic acid is no longer used as a surgical disinfectant because it is a skin irritant, but the chemical compounds found in antiseptic mouthwashes and throat lozenges are called phenolics.

Chemically, phenol consists of a benzene ring with an -OH group, and phenolics are compounds that have this group as part of their chemical structure. Phenolics such as thymol and eucalyptol occur naturally in plants. Other phenolics can be derived from creosote, a component of coal tar. Phenolics tend to be stable, persistent on surfaces, and less toxic than phenol. They inhibit microbial growth by denaturing proteins and disrupting membranes.

Since Lister's time, several phenolic compounds have been used to control microbial growth. Phenolics like cresols (methylated phenols) and o-phenylphenol were active ingredients in various formulations of Lysol since its invention in 1889. o-Phenylphenol was also commonly used in agriculture to control bacterial and fungal growth on harvested crops, especially citrus fruits, but its use in the United States is now far more limited. The bisphenol hexachlorophene, a disinfectant, is the active ingredient in pHisoHex, a topical cleansing detergent widely used for handwashing in hospital settings. pHisoHex is particularly effective against gram-positive bacteria, including those causing staphylococcal and streptococcal skin infections. pHisoHex was formerly used for bathing infants, but this practice has been discontinued because it has been shown that exposure to hexachlorophene can lead to neurological problems.

Triclosan is another bisphenol compound that has seen widespread application in antibacterial products over the last several decades. Initially used in toothpastes, triclosan is now commonly used in hand soaps and is frequently impregnated into a wide variety of other products, including cutting boards, knives, shower curtains, clothing, and concrete, to make them antimicrobial. It is particularly effective against gram-positive bacteria on the skin, as well as certain gram-negative bacteria and yeasts.

Triclosan: Antibacterial Overkill?

Hand soaps and other cleaning products are often marketed as "antibacterial," suggesting that they provide a level of cleanliness superior to that of conventional soaps and cleansers. But are the antibacterial ingredients in these products really safe and effective?

About 75% of antibacterial liquid hand soaps and 30% of bar soaps contain the chemical triclosan, a phenolic. Triclosan blocks an enzyme in the bacterial fatty acid-biosynthesis pathway that is not found in the comparable human pathway. Although the use of triclosan in the home increased dramatically during the 1990s, more than 40 years of research by the FDA have turned up no conclusive evidence that washing with triclosan-containing products provides increased health benefits compared with washing with traditional soap. Although some studies indicate that fewer bacteria may remain on a person's hands after washing with triclosan-based soap, compared with traditional soap, no evidence points to any reduction in the transmission of bacteria that cause respiratory and gastrointestinal illness. In short, soaps with triclosan may remove or kill a few more germs but not enough to reduce the spread of disease.

Perhaps more disturbing, some clear risks associated with triclosan-based soaps have come to light. The widespread use of triclosan has led to an increase in triclosan-resistant bacterial strains, including those of clinical importance, such as Salmonella enterica; this resistance may render triclosan useless as an antibacterial in the long run. Bacteria can easily gain resistance to triclosan through a change to a single gene encoding the targeted enzyme in the bacterial fatty acid-synthesis pathway. Other disinfectants with a less specific mode of action are much less prone to engendering resistance because it would take much more than a single genetic change.

Use of triclosan over the last several decades has also led to a buildup of the chemical in the environment. Triclosan in hand soap is directly introduced into wastewater and sewage systems as a result of the handwashing process. There, its antibacterial properties can inhibit or kill bacteria responsible for the decomposition of sewage, causing septic systems to clog and back up. Eventually, triclosan in wastewater finds its way into surface waters, streams, lakes, sediments, and soils, disrupting natural populations of bacteria that carry out important environmental functions, such as inhibiting algae. Triclosan also finds its way into the bodies of amphibians and fish, where it can act as an endocrine disruptor. Detectable levels of triclosan have also been found in various human bodily fluids, including breast milk, plasma, and urine. In fact, a study conducted by the CDC found detectable levels of triclosan in the urine of 75% of 2,517 people tested in 2003-2004. This finding is even more troubling given the evidence that triclosan may affect immune function in humans.

In December 2013, the FDA gave soap manufacturers until 2016 to prove that antibacterial soaps provide a significant benefit over traditional soaps; if unable to do so, manufacturers will be forced to remove these products from the market.

Heavy Metals

Some of the first chemical disinfectants and antiseptics to be used were heavy metals. Heavy metals kill microbes by binding to proteins, thus inhibiting enzymatic activity. Heavy metals are oligodynamic, meaning that very small concentrations show significant antimicrobial activity. Ions of heavy metals bind to sulfur-containing amino acids strongly and bioaccumulate within cells, allowing these metals to reach high localized concentrations. This causes proteins to denature.

Heavy metals are not selectively toxic to microbial cells. They may bioaccumulate in human or animal cells, as well, and excessive concentrations can have toxic effects on humans. If too much silver accumulates in the body, for example, it can result in a condition called argyria, in which the skin turns irreversibly blue-gray. One way to reduce the potential toxicity of heavy metals is by carefully controlling the duration of exposure and concentration of the heavy metal.

Mercury

Mercury is an example of a heavy metal that has been used for many years to control microbial growth. It was used for many centuries to treat syphilis. Mercury compounds like mercuric chloride are mainly bacteriostatic and have a very broad spectrum of activity. Various forms of mercury bind to sulfur-containing amino acids within proteins, inhibiting their functions.

In recent decades, the use of such compounds has diminished because of mercury's toxicity. It is toxic to the central nervous, digestive, and renal systems at high concentrations, and has negative environmental effects, including bioaccumulation in fish. Topical antiseptics such as mercurochrome, which contains mercury in low concentrations, and merthiolate, a tincture (a solution of mercury dissolved in alcohol) were once commonly used. However, because of concerns about using mercury compounds, these antiseptics are no longer sold in the United States.

Silver

Silver has long been used as an antiseptic. In ancient times, drinking water was stored in silver jugs. Silvadene cream is commonly used to treat topical wounds and is particularly helpful in preventing infection in burn wounds. Silver nitrate drops were once routinely applied to the eyes of newborns to protect against ophthalmia neonatorum, eye infections that can occur due to exposure to pathogens in the birth canal, but antibiotic creams are more now commonly used. Silver is often combined with antibiotics, making the antibiotics thousands of times more effective. Silver is also commonly incorporated into catheters and bandages, rendering them antimicrobial; however, there is evidence that heavy metals may also enhance selection for antibiotic resistance.

Copper, Nickel, and Zinc

Several other heavy metals also exhibit antimicrobial activity. Copper sulfate is a common algicide used to control algal growth in swimming pools and fish tanks. The use of metallic copper to minimize microbial growth is also becoming more widespread. Copper linings in incubators help reduce contamination of cell cultures. The use of copper pots for water storage in underdeveloped countries is being investigated as a way to combat diarrheal diseases. Copper coatings are also becoming popular for frequently handled objects such as doorknobs, cabinet hardware, and other fixtures in health-care facilities in an attempt to reduce the spread of microbes.

Nickel and zinc coatings are now being used in a similar way. Other forms of zinc, including zinc chloride and zinc oxide, are also used commercially. Zinc chloride is quite safe for humans and is commonly found in mouthwashes, substantially increasing their length of effectiveness. Zinc oxide is found in a variety of products, including topical antiseptic creams such as calamine lotion, diaper ointments, baby powder, and dandruff shampoos.

Halogens

Other chemicals commonly used for disinfection are the halogens iodine, chlorine, and fluorine. Iodine works by oxidizing cellular components, including sulfur-containing amino acids, nucleotides, and fatty acids, and destabilizing the macromolecules that contain these molecules. It is often used as a topical tincture, but it may cause staining or skin irritation. An iodophor is a compound of iodine complexed with an organic molecule, thereby increasing iodine's stability and, in turn, its efficacy. One common iodophor is povidone-iodine, which includes a wetting agent that releases iodine relatively slowly. Betadine is a brand of povidone-iodine commonly used as a hand scrub by medical personnel before surgery and for topical antisepsis of a patient's skin before incision.

Chlorine is another halogen commonly used for disinfection. When chlorine gas is mixed with water, it produces a strong oxidant called hypochlorous acid, which is uncharged and enters cells easily. Chlorine gas is commonly used in municipal drinking water and wastewater treatment plants, with the resulting hypochlorous acid producing the actual antimicrobial effect. Those working at water treatment facilities need to take great care to minimize personal exposure to chlorine gas. Sodium hypochlorite is the chemical component of common household bleach, and it is also used for a wide variety of disinfecting purposes. Hypochlorite salts, including sodium and calcium hypochlorites, are used to disinfect swimming pools. Chlorine gas, sodium hypochlorite, and calcium hypochlorite are also commonly used disinfectants in the food processing and restaurant industries to reduce the spread of foodborne diseases. Workers in these industries also need to take care to use these products correctly to ensure their own safety as well as the safety of consumers. A recent joint statement published by the Food and Agriculture Organization (FAO) of the United Nations and WHO indicated that none of the many beneficial uses of chlorine products in food processing to reduce the spread of foodborne illness posed risks to consumers.

Another class of chlorinated compounds called chloramines are widely used as disinfectants. Chloramines are relatively stable, releasing chlorine over long periods time. Chloramines are derivatives of ammonia by substitution of one, two, or all three hydrogen atoms with chlorine atoms.

Chloramines and other cholorine compounds may be used for disinfection of drinking water, and chloramine tablets are frequently used by the military for this purpose. After a natural disaster or other event that compromises the public water supply, the CDC recommends disinfecting tap water by adding small amounts of regular household bleach. Recent research suggests that sodium dichloroisocyanurate (NaDCC) may also be a good alternative for drinking water disinfection. Currently, NaDCC tablets are available for general use and for use by the military, campers, or those with emergency needs; for these uses, NaDCC is preferable to chloramine tablets. Chlorine dioxide, a gaseous agent used for fumigation and sterilization of enclosed areas, is also commonly used for the disinfection of water.

Although chlorinated compounds are relatively effective disinfectants, they have their disadvantages. Some may irritate the skin, nose, or eyes of some individuals, and they may not completely eliminate certain hardy organisms from contaminated drinking water. The fungus Cryptosporidium, for example, has a protective outer shell that makes it resistant to chlorinated disinfectants. Thus, boiling of drinking water in emergency situations is recommended when possible.

The halogen fluorine is also known to have antimicrobial properties that contribute to the prevention of dental caries (cavities). Fluoride is the main active ingredient of toothpaste and is also commonly added to tap water to help communities maintain oral health. Chemically, fluoride can become incorporated into the hydroxyapatite of tooth enamel, making it more resistant to corrosive acids produced by the fermentation of oral microbes. Fluoride also enhances the uptake of calcium and phosphate ions in tooth enamel, promoting remineralization. In addition to strengthening enamel, fluoride also seems to be bacteriostatic. It accumulates in plaque-forming bacteria, interfering with their metabolism and reducing their production of the acids that contribute to tooth decay.

Alcohols

Alcohols make up another group of chemicals commonly used as disinfectants and antiseptics. They work by rapidly denaturing proteins, which inhibits cell metabolism, and by disrupting membranes, which leads to cell lysis. Once denatured, the proteins may potentially refold if enough water is present in the solution. Alcohols are typically used at concentrations of about 70% aqueous solution and, in fact, work better in aqueous solutions than 100% alcohol solutions. This is because alcohols coagulate proteins. In higher alcohol concentrations, rapid coagulation of surface proteins prevents effective penetration of cells. The most commonly used alcohols for disinfection are ethyl alcohol (ethanol) and isopropyl alcohol (isopropanol, rubbing alcohol).

Alcohols tend to be bactericidal and fungicidal, but may also be viricidal for enveloped viruses only. Although alcohols are not sporicidal, they do inhibit the processes of sporulation and germination. Alcohols are volatile and dry quickly, but they may also cause skin irritation because they dehydrate the skin at the site of application. One common clinical use of alcohols is swabbing the skin for degerming before needle injection. Alcohols also are the active ingredients in instant hand sanitizers, which have gained popularity in recent years. The alcohol in these hand sanitizers works both by denaturing proteins and by disrupting the microbial cell membrane, but will not work effectively in the presence of visible dirt.

Last, alcohols are used to make tinctures with other antiseptics, such as the iodine tinctures discussed previously in this chapter. All in all, alcohols are inexpensive and quite effective for the disinfection of a broad range of vegetative microbes. However, one disadvantage of alcohols is their high volatility, limiting their effectiveness to immediately after application.

Think About It

Name at least three advantages of alcohols as disinfectants.

Describe several specific applications of alcohols used in disinfectant products.

Surfactants

Surface-active agents, or surfactants, are a group of chemical compounds that lower the surface tension of water. Surfactants are the major ingredients in soaps and detergents. Soaps are salts of long-chain fatty acids and have both polar and nonpolar regions, allowing them to interact with polar and nonpolar regions in other molecules. They can interact with nonpolar oils and grease to create emulsions in water, loosening and lifting away dirt and microbes from surfaces and skin. Soaps do not kill or inhibit microbial growth and so are not considered antiseptics or disinfectants. However, proper use of soaps mechanically carries away microorganisms, effectively degerming a surface. Some soaps contain added bacteriostatic agents such as triclocarban or cloflucarban, compounds structurally related to triclosan, that introduce antiseptic or disinfectant properties to the soaps.

Soaps, however, often form films that are difficult to rinse away, especially in hard water, which contains high concentrations of calcium and magnesium mineral salts. Detergents contain synthetic surfactant molecules with both polar and nonpolar regions that have strong cleansing activity but are more soluble, even in hard water, and, therefore, leave behind no soapy deposits. Anionic detergents, such as those used for laundry, have a negatively charged anion at one end attached to a long hydrophobic chain, whereas cationic detergents have a positively charged cation instead. Cationic detergents include an important class of disinfectants and antiseptics called the quaternary ammonium salts (quats), named for the characteristic quaternary nitrogen atom that confers the positive charge. Overall, quats have properties similar to phospholipids, having hydrophilic and hydrophobic ends. As such, quats have the ability to insert into the bacterial phospholipid bilayer and disrupt membrane integrity. The cationic charge of quats appears to confer their antimicrobial properties, which are diminished when neutralized. Quats have several useful properties. They are stable, nontoxic, inexpensive, colorless, odorless, and tasteless. They tend to be bactericidal by disrupting membranes. They are also active against fungi, protozoans, and enveloped viruses, but endospores are unaffected. In clinical settings, they may be used as antiseptics or to disinfect surfaces. Mixtures of quats are also commonly found in household cleaners and disinfectants, including many current formulations of Lysol brand products, which contain benzalkonium chlorides as the active ingredients. Benzalkonium chlorides, along with the quat cetylpyrimidine chloride, are also found in products such as skin antiseptics, oral rinses, and mouthwashes.

Handwashing the Right Way

Handwashing is critical for public health and should be emphasized in a clinical setting. For the general public, the CDC recommends handwashing before, during, and after food handling; before eating; before and after interacting with someone who is ill; before and after treating a wound; after using the toilet or changing diapers; after coughing, sneezing, or blowing the nose; after handling garbage; and after interacting with an animal, its feed, or its waste. Figure 9 illustrates the five steps of proper handwashing recommended by the CDC.

Handwashing is even more important for health-care workers, who should wash their hands thoroughly between every patient contact, after the removal of gloves, after contact with bodily fluids and potentially infectious fomites, and before and after assisting a surgeon with invasive procedures. Even with the use of proper surgical attire, including gloves, scrubbing for surgery is more involved than routine handwashing. The goal of surgical scrubbing is to reduce the normal microbiota on the skin's surface to prevent the introduction of these microbes into a patient's surgical wounds.

There is no single widely accepted protocol for surgical scrubbing. Protocols for length of time spent scrubbing may depend on the antimicrobial used; health-care workers should always check the manufacturer's recommendations. According to the Association of Surgical Technologists (AST), surgical scrubs may be performed with or without the use of brushes.

To learn more about proper handwashing, visit the CDC's website.

Bisbiguanides

Bisbiguanides were first synthesized in the 20th century and are cationic (positively charged) molecules known for their antiseptic properties. One important bisbiguanide antiseptic is chlorhexidine. It has broad-spectrum activity against yeasts, gram-positive bacteria, and gram-negative bacteria, with the exception of Pseudomonas aeruginosa, which may develop resistance on repeated exposure. Chlorhexidine disrupts cell membranes and is bacteriostatic at lower concentrations or bactericidal at higher concentrations, in which it actually causes the cells' cytoplasmic contents to congeal. It also has activity against enveloped viruses. However, chlorhexidine is poorly effective against Mycobacterium tuberculosis and nonenveloped viruses, and it is not sporicidal. Chlorhexidine is typically used in the clinical setting as a surgical scrub and for other handwashing needs for medical personnel, as well as for topical antisepsis for patients before surgery or needle injection. It is more persistent than iodophors, providing long-lasting antimicrobial activity. Chlorhexidine solutions may also be used as oral rinses after oral procedures or to treat gingivitis. Another bisbiguanide, alexidine, is gaining popularity as a surgical scrub and an oral rinse because it acts faster than chlorhexidine.

Alkylating Agents

The alkylating agents are a group of strong disinfecting chemicals that act by replacing a hydrogen atom within a molecule with an alkyl group (C nH 2n+1), thereby inactivating enzymes and nucleic acids. The alkylating agent formaldehyde (CH ₂OH) is commonly used in solution at a concentration of 37% (known as formalin) or as a gaseous disinfectant and biocide. It is a strong, broad-spectrum disinfectant and biocide that has the ability to kill bacteria, viruses, fungi, and endospores, leading to sterilization at low temperatures, which is sometimes a convenient alternative to the more labor-intensive heat sterilization methods. It also cross-links proteins and has been widely used as a chemical fixative. Because of this, it is used for the storage of tissue specimens and as an embalming fluid. It also has been used to inactivate infectious agents in vaccine preparation. Formaldehyde is very irritating to living tissues and is also carcinogenic; therefore, it is not used as an antiseptic.

Glutaraldehyde is structurally similar to formaldehyde but has two reactive aldehyde groups, allowing it to act more quickly than formaldehyde. It is commonly used as a 2% solution for sterilization and is marketed under the brand name Cidex. It is used to disinfect a variety of surfaces and surgical and medical equipment. However, similar to formaldehyde, glutaraldehyde irritates the skin and is not used as an antiseptic.

A new type of disinfectant gaining popularity for the disinfection of medical equipment is o-phthalaldehyde (OPA), which is found in some newer formulations of Cidex and similar products, replacing glutaraldehyde. o-Phthalaldehyde also has two reactive aldehyde groups, but they are linked by an aromatic bridge. o-Phthalaldehyde is thought to work similarly to glutaraldehyde and formaldehyde, but is much less irritating to skin and nasal passages, produces a minimal odor, does not require processing before use, and is more effective against mycobacteria.

Ethylene oxide is a type of alkylating agent that is used for gaseous sterilization. It is highly penetrating and can sterilize items within plastic bags such as catheters, disposable items in laboratories and clinical settings (like packaged Petri dishes), and other pieces of equipment. Ethylene oxide exposure is a form of cold sterilization, making it useful for the sterilization of heat-sensitive items. Great care needs to be taken with the use of ethylene oxide, however; it is carcinogenic, like the other alkylating agents, and is also highly explosive. With careful use and proper aeration of the products after treatment, ethylene oxide is highly effective, and ethylene oxide sterilizers are commonly found in medical settings for sterilizing packaged materials.

β-Propionolactone is an alkylating agent with a different chemical structure than the others already discussed. Like other alkylating agents, β-propionolactone binds to DNA, thereby inactivating it. It is a clear liquid with a strong odor and has the ability to kill endospores. As such, it has been used in either liquid form or as a vapor for the sterilization of medical instruments and tissue grafts, and it is a common component of vaccines, used to maintain their sterility. It has also been used for the sterilization of nutrient broth, as well as blood plasma, milk, and water. It is quickly metabolized by animals and humans to lactic acid. It is also an irritant, however, and may lead to permanent damage of the eyes, kidneys, or liver. Additionally, it has been shown to be carcinogenic in animals; thus, precautions are necessary to minimize human exposure to β-propionolactone.

Think About It

What chemical reaction do alkylating agents participate in?

Why are alkylating agents not used as antiseptics?

Diehard Prions

Prions, the acellular, misfolded proteins responsible for incurable and fatal diseases such as kuru and Creutzfeldt-Jakob disease (see Viroids, Virusoids, and Prions), are notoriously difficult to destroy. Prions are extremely resistant to heat, chemicals, and radiation. They are also extremely infectious and deadly; thus, handling and disposing of prion-infected items requires extensive training and extreme caution.

Typical methods of disinfection can reduce but not eliminate the infectivity of prions. Autoclaving is not completely effective, nor are chemicals such as phenol, alcohols, formalin, and β-propiolactone. Even when fixed in formalin, affected brain and spinal cord tissues remain infectious.

Personnel who handle contaminated specimens or equipment or work with infected patients must wear a protective coat, face protection, and cut-resistant gloves. Any contact with skin must be immediately washed with detergent and warm water without scrubbing. The skin should then be washed with 1 N NaOH or a 1:10 dilution of bleach for 1 minute. Contaminated waste must be incinerated or autoclaved in a strong basic solution, and instruments must be cleaned and soaked in a strong basic solution.

For more information on the handling of animals and prion-contaminated materials, visit the guidelines published on the CDC and WHO websites.

Peroxygens

Peroxygens are strong oxidizing agents that can be used as disinfectants or antiseptics. The most widely used peroxygen is hydrogen peroxide (H ₂O ₂), which is often used in solution to disinfect surfaces and may also be used as a gaseous agent. Hydrogen peroxide solutions are inexpensive skin antiseptics that break down into water and oxygen gas, both of which are environmentally safe. This decomposition is accelerated in the presence of light, so hydrogen peroxide solutions typically are sold in brown or opaque bottles. One disadvantage of using hydrogen peroxide as an antiseptic is that it also causes damage to skin that may delay healing or lead to scarring. Contact lens cleaners often include hydrogen peroxide as a disinfectant.

Hydrogen peroxide works by producing free radicals that damage cellular macromolecules. Hydrogen peroxide has broad-spectrum activity, working against gram-positive and gram-negative bacteria (with slightly greater efficacy against gram-positive bacteria), fungi, viruses, and endospores. However, bacteria that produce the oxygen-detoxifying enzymes catalase or peroxidase may have inherent tolerance to low hydrogen peroxide concentrations. To kill endospores, the length of exposure or concentration of solutions of hydrogen peroxide must be increased. Gaseous hydrogen peroxide has greater efficacy and can be used as a sterilant for rooms or equipment.

Plasma, a hot, ionized gas, described as the fourth state of matter, is useful for sterilizing equipment because it penetrates surfaces and kills vegetative cells and endospores. Hydrogen peroxide and peracetic acid, another commonly used peroxygen, each may be introduced as a plasma. Peracetic acid can be used as a liquid or plasma sterilant insofar as it readily kills endospores, is more effective than hydrogen peroxide even at rather low concentrations, and is immune to inactivation by catalases and peroxidases. It also breaks down to environmentally innocuous compounds; in this case, acetic acid and oxygen.

Other examples of peroxygens include benzoyl peroxide and carbamide peroxide. Benzoyl peroxide is a peroxygen that used in acne medication solutions. It kills the bacterium Propionibacterium acnes, which is associated with acne. Carbamide peroxide, an ingredient used in toothpaste, is a peroxygen that combats oral biofilms that cause tooth discoloration and halitosis (bad breath). Last, ozone gas is a peroxygen with disinfectant qualities and is used to clean air or water supplies. Overall, peroxygens are highly effective and commonly used, with no associated environmental hazard.

Supercritical Fluids

Within the last 15 years, the use of supercritical fluids, especially supercritical carbon dioxide (scCO ₂), has gained popularity for certain sterilizing applications. When carbon dioxide is brought to approximately 10 times atmospheric pressure, it reaches a supercritical state that has physical properties between those of liquids and gases. Materials put into a chamber in which carbon dioxide is pressurized in this way can be sterilized because of the ability of scCO ₂ to penetrate surfaces.

Supercritical carbon dioxide works by penetrating cells and forming carbonic acid, thereby lowering the cell pH considerably. This technique is effective against vegetative cells and is also used in combination with peracetic acid to kill endospores. Its efficacy can also be augmented with increased temperature or by rapid cycles of pressurization and depressurization, which more likely produce cell lysis.

Benefits of scCO ₂ include the nonreactive, nontoxic, and nonflammable properties of carbon dioxide, and this protocol is effective at low temperatures. Unlike other methods, such as heat and irradiation, that can degrade the object being sterilized, the use of scCO ₂ preserves the object's integrity and is commonly used for treating foods (including spices and juices) and medical devices such as endoscopes. It is also gaining popularity for disinfecting tissues such as skin, bones, tendons, and ligaments prior to transplantation. scCO ₂ can also be used for pest control because it can kill insect eggs and larvae within products.

Chemical Food Preservatives

Chemical preservatives are used to inhibit microbial growth and minimize spoilage in some foods. Commonly used chemical preservatives include sorbic acid, benzoic acid, and propionic acid, and their more soluble salts potassium sorbate, sodium benzoate, and calcium propionate, all of which are used to control the growth of molds in acidic foods. Each of these preservatives is nontoxic and readily metabolized by humans. They are also flavorless, so they do not compromise the flavor of the foods they preserve.

Sorbic and benzoic acids exhibit increased efficacy as the pH decreases. Sorbic acid is thought to work by inhibiting various cellular enzymes, including those in the citric acid cycle, as well as catalases and peroxidases. It is added as a preservative in a wide variety of foods, including dairy, bread, fruit, and vegetable products. Benzoic acid is found naturally in many types of fruits and berries, spices, and fermented products. It is thought to work by decreasing intracellular pH, interfering with mechanisms such as oxidative phosphorylation and the uptake of molecules such as amino acids into cells. Foods preserved with benzoic acid or sodium benzoate include fruit juices, jams, ice creams, pastries, soft drinks, chewing gum, and pickles.

Propionic acid is thought to both inhibit enzymes and decrease intracellular pH, working similarly to benzoic acid. However, propionic acid is a more effective preservative at a higher pH than either sorbic acid or benzoic acid. Propionic acid is naturally produced by some cheeses during their ripening and is added to other types of cheese and baked goods to prevent mold contamination. It is also added to raw dough to prevent contamination by the bacterium Bacillus mesentericus, which causes bread to become ropy.

Other commonly used chemical preservatives include sulfur dioxide and nitrites. Sulfur dioxide prevents browning of foods and is used for the preservation of dried fruits; it has been used in winemaking since ancient times. Sulfur dioxide gas dissolves in water readily, forming sulfites. Although sulfites can be metabolized by the body, some people have sulfite allergies, including asthmatic reactions. Additionally, sulfites degrade thiamine, an important nutrient in some foods. The mode of action of sulfites is not entirely clear, but they may interfere with the disulfide bond formation in proteins, inhibiting enzymatic activity. Alternatively, they may reduce the intracellular pH of the cell, interfering with proton motive force-driven mechanisms.

Nitrites are added to processed meats to maintain color and stop the germination of Clostridium botulinum endospores. Nitrites are reduced to nitric oxide, which reacts with heme groups and iron-sulfur groups. When nitric oxide reacts with the heme group within the myoglobin of meats, a red product forms, giving meat its red color. Alternatively, it is thought that when nitric acid reacts with the iron-sulfur enzyme ferredoxin within bacteria, this electron transport-chain carrier is destroyed, preventing ATP synthesis. Nitrosamines, however, are carcinogenic and can be produced through exposure of nitrite-preserved meats (e.g., hot dogs, lunch meat, breakfast sausage, bacon, meat in canned soups) to heat during cooking.

Natural Chemical Food Preservatives

The discovery of natural antimicrobial substances produced by other microbes has added to the arsenal of preservatives used in food. Nisin is an antimicrobial peptide produced by the bacterium Lactococcus lactis and is particularly effective against gram-positive organisms. Nisin works by disrupting cell wall production, leaving cells more prone to lysis. It is used to preserve cheeses, meats, and beverages.

Natamycin is an antifungal macrolide antibiotic produced by the bacterium Streptomyces natalensis. It was approved by the FDA in 1982 and is used to prevent fungal growth in various types of dairy products, including cottage cheese, sliced cheese, and shredded cheese. Natamycin is also used for meat preservation in countries outside the United States.

Key Concepts and Summary

Heavy metals, including mercury, silver, copper, and zinc, have long been used for disinfection and preservation, although some have toxicity and environmental risks associated with them.

Halogens, including chlorine, fluorine, and iodine, are also commonly used for disinfection. Chlorine compounds, including sodium hypochlorite, chloramines, and chlorine dioxide, are commonly used for water disinfection. Iodine, in both tincture and iodophor forms, is an effective antiseptic.

Alcohols, including ethyl alcohol and isopropyl alcohol, are commonly used antiseptics that act by denaturing proteins and disrupting membranes.

Phenolics are stable, long-acting disinfectants that denature proteins and disrupt membranes. They are commonly found in household cleaners, mouthwashes, and hospital disinfectants, and are also used to preserve harvested crops.

The phenolic compound triclosan, found in antibacterial soaps, plastics, and textiles is technically an antibiotic because of its specific mode of action of inhibiting bacterial fatty-acid synthesis..

Surfactants, including soaps and detergents, lower the surface tension of water to create emulsions that mechanically carry away microbes. Soaps are long-chain fatty acids, whereas detergents are synthetic surfactants.

Quaternary ammonium compounds (quats) are cationic detergents that disrupt membranes. They are used in household cleaners, skin disinfectants, oral rinses, and mouthwashes.

Bisbiguanides disrupt cell membranes, causing cell contents to gel. Chlorhexidine and alexidine are commonly used for surgical scrubs, for handwashing in clinical settings, and in prescription oral rinses.

Alkylating agents effectively sterilize materials at low temperatures but are carcinogenic and may also irritate tissue. Glutaraldehyde and o-phthalaldehyde are used as hospital disinfectants but not as antiseptics. Formaldehyde is used for the storage of tissue specimens, as an embalming fluid, and in vaccine preparation to inactivate infectious agents. Ethylene oxide is a gas sterilant that can permeate heat-sensitive packaged materials, but it is also explosive and carcinogenic.

Peroxygens, including hydrogen peroxide, peracetic acid, benzoyl peroxide, and ozone gas, are strong oxidizing agents that produce free radicals in cells, damaging their macromolecules. They are environmentally safe and are highly effective disinfectants and antiseptics.

Pressurized carbon dioxide in the form of a supercritical fluid easily permeates packaged materials and cells, forming carbonic acid and lowering intracellular pH. Supercritical carbon dioxide is nonreactive, nontoxic, nonflammable, and effective at low temperatures for sterilization of medical devices, implants, and transplanted tissues.

Chemical preservatives are added to a variety of foods. Sorbic acid, benzoic acid, propionic acid, and their more soluble salts inhibit enzymes or reduce intracellular pH.

Sulfites are used in winemaking and food processing to prevent browning of foods.

Nitrites are used to preserve meats and maintain color, but cooking nitrite-preserved meats may produce carcinogenic nitrosamines.

Nisin and natamycin are naturally produced preservatives used in cheeses and meats. Nisin is effective against gram-positive bacteria and natamycin against fungi.

Multiple Choice

Which of the following refers to a disinfecting chemical dissolved in alcohol?

Which of the following peroxygens is widely used as a household disinfectant, is inexpensive, and breaks down into water and oxygen gas?

Which of the following chemical food preservatives is used in the wine industry but may cause asthmatic reactions in some individuals?

Bleach is an example of which group of chemicals used for disinfection?

Which chemical disinfectant works by methylating enzymes and nucleic acids and is known for being toxic and carcinogenic?

Fill in the Blank

Doorknobs and other surfaces in clinical settings are often coated with ________, ________, or ________ to prevent the transmission of microbes.

True/False

Soaps are classified as disinfectants.

Mercury-based compounds have fallen out of favor for use as preservatives and antiseptics.

Think About It

1. Which solution of ethyl alcohol is more effective at inhibiting microbial growth: a 70% solution or a 100% solution? Why?

2. When might a gas treatment be used to control microbial growth instead of autoclaving? What are some examples?

3. What is the advantage of using an iodophor rather than iodine or an iodine tincture?

4. Looking at Figure 11, which alkylating agent shown lacks an aldehyde group?

5. Do you think naturally produced antimicrobial products like nisin and natamycin should replace sorbic acid for food preservation? Why or why not?

6. Why is the use of skin disinfecting compounds required for surgical scrubbing and not for everyday handwashing?

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In addition to physical methods of microbial control, chemicals are also used to control microbial growth. A wide variety of chemicals can be used as disinfectants or antiseptics. When choosing which to use, it is important to consider the type of microbe targeted; how clean the item needs to be; the disinfectant's effect on the item's integrity; its safety to animals, humans, and the environment; its expense; and its ease of use.

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- Bacterias are prokaryotes
- It is a single cell organism and it lacks a nucleus

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(Image credit: Centers for Disease Control)

Bacteria are microscopic, single-celled organisms that thrive in diverse environments. These organisms can live in soil, the ocean and inside the human gut.

Humans' relationship with bacteria is complex. Sometimes bacteria lend us a helping hand, such as by curdling milk into yogurt or helping with our digestion. In other cases, bacteria are destructive, causing diseases like pneumonia and methicillin-resistant Staphylococcus aureus (MRSA).

Structure

Bacteria (singular: bacterium) are classified as prokaryotes, which are single-celled organisms with a simple internal structure that lacks a nucleus, and contains DNA that either floats freely in a twisted, thread-like mass called the nucleoid, or in separate, circular pieces called plasmids. Ribosomes are the spherical units in the bacterial cell where proteins are assembled from individual amino acids using the information encoded in ribosomal RNA.

Bacterial cells are generally surrounded by two protective coverings: an outer cell wall and an inner cell membrane. Certain bacteria, like the mycoplasmas, do not have a cell wall at all. Some bacteria may even have a third, outermost protective layer called the capsule. Whip-like extensions often cover the surfaces of bacteria - long ones called flagella or short ones called pili - that help bacteria to move around and attach to a host.

Classification

A few different criteria are used to classify bacteria. The organisms can be distinguished by the nature of their cell walls, by their shape, or by differences in their genetic makeup.

The Gram stain is a test used to identify bacteria by the composition of their cell walls, named for Hans Christian Gram, who developed the technique in 1884. The test stains Gram-positive bacteria, or bacteria that do not have an outer membrane. Gram-negative bacteria don't pick up the stain. For example, Streptococcus pneumoniae ( S. pneumoniae), which causes pneumonia, is a Gram-positive bacterium, but Escherichia coli () and Vibrio cholerae, which causes cholera, are Gram-negative bacteria.

There are three basic bacterial shapes: Round bacteria called cocci (singular: coccus), cylindrical, capsule-shaped ones known as bacilli (singular: bacillus); and spiral bacteria, aptly called spirilla (singular: spirillum). The shapes and configurations of bacteria are often reflected in their names. For example, the milk-curdling Lactobacillus acidophilus are bacilli, and pneumonia-causing S. pneumoniae are a chain of cocci. Some bacteria take other shapes, such as stalked, square or star.

(Image credit: Kateryna Kon/Shutterstock)

Reproduction

Most bacteria multiply by a process called binary fission, according to the Cornell University College of Agriculture and Life Sciences. In this process, a single bacterial cell, called the "parent," makes a copy of its DNA and grows larger by doubling its cellular content. The cell then splits apart, pushing the duplicated material out and creating two identical "daughter" cells.

Some bacterial species, such as cyanobacteria and firmicutes, reproduce via budding. In this case, the daughter cell grows as an offshoot of the parent. It starts off as a small nub, grows until it is the same size as its parent, and splits off.

The DNA found in parents and offspring after binary fission or budding is exactly the same. Therefore, bacterial cells introduce variation into their genetic material by integrating additional DNA, often from their surroundings, into their genome. This is known as horizontal gene transfer; the resulting genetic variation ensures that bacteria can adapt and survive as their environment changes. [ Watch Strange, Glowing Bacteria Harpoon and Swallow DNA to Evolve]

There are three ways horizontal gene transfer occurs: transformation, transduction and conjugation.

Transformation is the most common process of horizontal gene transfer and occurs when short DNA fragments are exchanged between donors and recipients. Transduction, which typically only occurs between closely related bacteria, requires the donor and recipient to transfer DNA by sharing cell surface receptors. Conjugation requires physical contact between the cell walls of bacteria; the DNA transfers from the donor cell to the recipient. Through conjugation, a bacterial cell can transfer DNA to eukaryotic cells (multi-celled organisms). Conjugation aids in the spread of antibiotic-resistance genes.

Bacteria in human health and disease

Bacteria can be beneficial as well as detrimental to human health. Commensal, or "friendly" bacteria, share space and resources within our bodies and tend to be helpful. There are about 10 times more microbial cells than human cells in our bodies; the highest numbers of microbial species are found in the gut, according to microbiologist David A. Relman's 2012 article in Nature.

The human gut is a comfortable setting for bacteria, with plenty of nutrients available for their sustenance. In a 2014 review article published in the American Journal of Gastroenterology, the authors mention that gut bacteria and other microorganisms, such as helpful strains of E.coli and Streptococcus, aid in digestion, stave off colonization by harmful pathogens, and help to develop the immune system. Moreover, the disruption of gut bacteria has been linked to certain disease conditions. For instance, patients with Crohn's disease have an increased immune response against gut bacteria, according to a 2003 review published in the journal The Lancet.

Other bacteria can cause infections. Several bacteria - ranging from so-called group A Streptococcus, Clostridium perfringens ( C. perfringens), E. coli and S. aureuscan cause a rare but severe soft tissue infection called necrotizing fasciitis (sometimes called flesh-eating bacteria). According to the Centers for Disease Control and Prevention (CDC), this infection affects the tissues surrounding muscles, nerves, fat and blood vessels; it can be treated, especially when caught early.

(Image credit: Alissa Eckert and Jennifer Oosthuizen/CDC)

Antibiotic resistance

Antibiotics are typically used to treat bacterial infections. However, in recent years, improper and unnecessary use of antibiotics has promoted the spread of several strains of antibiotic-resistant bacteria.

In cases of antibiotic resistance, the infectious bacteria are no longer susceptible to previously effective antibiotics. According to the CDC, at least 2 million people in the U.S. are infected with antibiotic-resistant bacteria every year, leading to the death of at least 23,000 people.

"Pretty much any infection you can think of now has been identified as being associated with some level of resistance," said Dr. Christopher Crnich, an infectious disease physician and hospital epidemiologist at the University of Wisconsin Hospitals and Madison Veterans Affairs Hospital. "There's very few infections that we now treat where infections caused by resistant bacteria is not a clinical concern."

MRSA, for example, is one of the more notorious antibiotic-resistant bacterial strains; it resists methicillin and other antibiotics used to treat Staphylococcus infections, which are acquired primarily through skin contact. MRSA infections occur in health-care settings such as hospitals and nursing homes, where it can lead to pneumonia or bloodstream infections. MRSA also spreads in the community, especially in situations where there is a lot of exposed skin, other physical contact, and the use of shared equipment - for example, among athletes, in tattoo parlors, and in day care facilities and schools. Community-acquired MRSA most often causes serious skin infections.

An important facet of combating antibiotic resistance is to be careful about their use. "It's so important for us to use antibiotics intelligently," Crnich told LiveScience. "You only want to use an antibiotic when you have a clear-cut bacterial infection."
Additional resources: This article was updated on Apr. 25, 2019, by Live Science Contributor Rachel Ross.

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(Image credit: Centers for Disease Control) Bacteria are microscopic, single-celled organisms that thrive in diverse environments. These organisms can live in soil, the ocean and inside the human gut. Humans' relationship with bacteria is complex. Sometimes bacteria lend us a helping hand, such as by curdling milk into yogurt or helping with our digestion.

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Disinfectants are common tools in household cleaning and maintenance. They make spaces and surfaces safe for people, especially for children and the elderly or infirm. There are a variety of classes of disinfectants, from natural and nontoxic disinfectants to industrial grade disinfectants with high toxicity. Depending on your needs, you may want to have a variety of disinfectants at the ready to maintain cleanliness in your home or workspace.

Disinfectants are used for one simple reason: to clean bacteria from surfaces, crevices and other parts of the environment. Every single part of our natural and built environment contains bacteria. These bacteria are generally harmless, and in some cases, they're even beneficial to optimal health. However, there are bad bacteria, which are dangerous to humans and can cause diseases and even death.

These dangerous bacteria are called pathogens, and eradicating them is the goal of disinfectant. By cleaning the environment and ridding it of bad bacteria, you can go a long way to ensuring that you and your family are safe from the difficulty of illness-causing bacteria. This is especially important if you have young children, an elderly person or someone with an illness in your home. These people have compromised immune systems and are most likely to be negatively affected by pathogens.

Disinfectants are also a popular way to clean houses. While cleaning household surfaces with disinfectants is rarely necessary, it may sometimes be appropriate to clean countertops, sinks and butcher blocks with a disinfectant. This is a good idea particularly if raw meat or other organic matter that has potentially contaminating properties were present. Otherwise, too much disinfectant use can kill good bacteria that humans should be exposed to, and this can cause further complications.

Disinfectants contain chemicals and chemical compounds that kill bacteria, mold and fungus. These compounds work together with other chemicals in the disinfecting agent to clean the area of any potentially dangerous bacteria. Some disinfectants are used alone, while others are combined with additional cleaning agents to make a useful household product that also disinfects.

Disinfectants work by taking an active ingredient and applying it to the affected area so that it kills or disrupts the cells in the bacteria. Certain disinfectants are stronger than others, and these are the ones that must be used to disinfect highly dangerous areas, such as in hospitals or where dangerous liquid has been spilled. Other disinfectants are of a lower grade of strength and can be used to clean tabletops and other areas where no dangerous pathogens are routinely or intentionally present.

Disinfectants exist to keep people safe from dangerous bacteria and fungus. However, if not used properly, disinfectants themselves can be harmful to human beings. Disinfectants like formaldehyde and chlorine can be dangerous and deadly in large doses or when used without proper ventilation and skin protection. All disinfectants contain high levels of ingredients that can be toxic when consumed in large quantities.

There are a number of classes of chemical disinfectants. These are the types of products with active ingredients that disrupt, damage or kill the bacteria to which they're applied. There are also other disinfectants that provide "inactivating agents" that can clean and disinfect without a primary chemical agent.

One type of disinfectant is the Quaternary Ammonium Compounds. These are the types of disinfecting agents seen in places like hospitals, nursing homes and other health and wellness centers. These "quats" are often paired with cleaning agents to make a product that's both cleansing and disinfecting. Another variety of disinfectant is a chlorine compound. These are strong compounds that can kill viruses that linger in a bodily fluid. These should only be applied with proper protection and ventilation.

Alcohols are another popular and prominent type of disinfectant. Alcohols are typically diluted with water and can kill strong bacteria in high concentrations. However, alcohol evaporates quickly and thus a good amount is necessary to be effective. They're flammable and can sometimes be ineffective when attempting to kill or disinfect organic matter.

Some classic examples of disinfectants are isopropyl alcohol, hydrogen peroxide and iodine. Iodine is rarely used as a common disinfectant these days since it can stain and has an unpleasant odor. Hydrogen peroxide has limited efficacy when confronted with significant bacteria, dangerous pathogens or bodily fluid.

Some common household disinfectants include bleach, ammonia, baking soda, soap and vinegar. While some of these are only mildly effective against pathogens, dangerous bacteria is less likely to appear in a home, so heavy industrial disinfectant chemicals aren't usually necessary. Clorox wipes are an example of a household product that uses a common disinfectant. Lysol is another product that has bacteria-killing properties but is also used to banish odors and dirt.

Bleach is probably the most common example of a type of disinfectant found in homes. It can be very effective at cleaning surfaces where organic matter has lived, including kitchen cutting boards, sinks, toilets and bathtubs. However, bleach can be irritating to the skin and corrosive to some household materials, so it's important to test it and use it only in a well-ventilated space.

Pine-Sol is one of the most recognizable brand names in household disinfectants. While there are a number of classes of disinfectants, Pine-Sol is generally not included in the list of industrial disinfectant chemicals. Pine-Sol is a cleansing and disinfectant agent that used to contain pine oil from pine tree needles. Pine oil has disinfectant properties and can be used as a deodorizer, insect repellent and laundry detergent.

Pine-Sol can also be used as a laundry detergent and a surface cleaning agent to ensure that any bacteria that could be dangerous is destroyed. Human beings are susceptible to viruses, which come from pathogens, and Pine-Sol, like other disinfecting agents, can kill viruses. This makes it ideal for floors where people have tracked dirt from outside, especially from places where pets walk.

Today, Pine-Sol and other similar pine-scented cleaning agents no longer contain pine oil. If they do, it's a very small percentage for the volume. This is because scientists have developed synthetic ingredients that can do the same job without the overpowering smell.

Disinfectants in the laundry are increasingly popular. If bodily fluids or other organic matter is present on clothes or linens, it's critical to get these items disinfected when cleaning in the washing machine. Bacterial infections from colds and viruses can linger on clothing and bedsheets, so it's crucial to wash those items in a disinfectant in order to prevent the spread of illness.

Pine oil disinfectants are available, although they do have a pervasive odor. Phenolic disinfectants like Lysol and other similar brands are effective on colors as well as whites. Chlorine bleach and other similar disinfectants are perhaps the most popular laundry-based household disinfectants.

The active ingredient in chlorine bleach products is sodium hypochlorite. In order for the ingredient to be effective, there needs to be at least a 5.25 to 6.15 percent presence of hypochlorite in the solution. Many commercial cleansers don't have the proper ratio, so it's important to check labels before you buy. Anything with less of the active ingredient won't effectively disinfect your clothing.

Hospitals and health care facilities are perhaps the places where it's most critical that effective chemical disinfectants are used. The presence of illnesses, a plethora of organic matter and a population of infirm people with compromised immune systems make sterilization profoundly important. But because of the variety of things that need to be disinfected in a hospital setting, a combination of various disinfectants is employed.

Most common in hospital settings are disinfectants like alcohol, chlorine, formaldehyde, hydrogen peroxide, peracetic acid and quats. Precautions must be taken to ensure that proper ventilation and skin protection is always utilized so that any risk to the safety of health care practitioners, patients or maintenance crew is limited and contained.

Certain diseases such as asthma have been associated with exposure to disinfectants, so hospitals and other health care facilities must be very careful about the concentrations of chemicals in the products they use. Reactive airway diseases can occur quickly and without warning in sensitive people, so it's best to keep an eye on any workers who are exposed to harsh chemicals to ensure their safety.

Disinfectants can range from benign and even edible to dangerous and highly toxic. Mild disinfectants like vinegar, baking soda and hydrogen peroxide aren't typically dangerous, particularly when an individual is exposed to only small doses and amounts. However, as mentioned earlier, chemicals like formaldehyde, chlorine bleach and alcohol can be extremely dangerous.

The best way to protect against skin irritation or respiratory illness while using disinfectants is to be sure that you're using the best possible practices for health and safety when cleaning and disinfecting. Always wear gloves no matter what solution you're using. Always ensure that rooms are properly ventilated. Open windows and doors as necessary, and turn on fans or other means of circulation to ensure that air with chemicals doesn't get trapped in the vicinity.

In many cases, chemicals can cause eyes to water. For this reason, it's a very good idea to wear goggles or other protective eyewear. When you've finished using a disinfectant, be sure to wash your hands and any exposed skin and to clean off any instruments that were exposed to the chemicals so you can be sure that everything is clean.

The safest disinfectants are ones that occur naturally and have low toxicity. For household cleaning, white vinegar and baking soda are excellent cleaning agents that disinfect while not exposing people to dangerous chemicals. Alcohols and hydrogen peroxide, particularly when diluted properly, are also among the safest disinfectants. These household disinfectants have a low incidence of irritating chemicals and are rarely toxic, so their use is encouraged.

As with any chemical compound, disinfectants are only as safe as their users. If you use a disinfectant properly, taking the necessary precautions and employing the chemicals carefully, you're likely to stay safe throughout. Reckless use of disinfectants, including combining disinfecting agents that shouldn't go together like ammonia and bleach, is when difficulties start. By safely handling the chemicals you clean with, you can be sure that you're disinfecting in a way that's safe for you and your family.

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Disinfectants are common tools in household cleaning and maintenance. They make spaces and surfaces safe for people, especially for children and the elderly or infirm. There are a variety of classes of disinfectants, from natural and nontoxic disinfectants to industrial grade disinfectants with high toxicity.

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Quats (quaternary ammonium compounds) are potent disinfectant chemicals commonly found in disinfectant wipes, sprays and other household cleaners that are designed to kill germs. It is often the stuff that allows a product to claim to be antibacterial, as they are certified by the EPA as pesticides.

Broad Range Quaternary Sanitizer - Clean Quick - EPA Registered - Buy Now! Clean Quick Broad Range Quaternary Sanitizer from P&G Professional. Buy Now! Buy P&G Pro Online Now. Trusted Brands! Complete Solutions!

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Please click here if you are not redirected within a few seconds. Quats (quaternary ammonium compounds) are potent disinfectant chemicals commonly found in disinfectant wipes, sprays and other household cleaners that are designed to kill germs. It is often the stuff that allows a product to claim to be antibacterial, as they are certified by the EPA as pesticides.

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Chlorine Based Sanitizers - Google Search