Klebsiella aerogenes is ID’d by using biochemical tests in the lab. It’s oxidase negative, catalase positive, citrate positive, and indole negative. On certain types of agar the colonies look pink because the bacteria can ferment lactose. It looks very similar to other bacteria in the Enterobacter and Klebsiella families, which is why it used to be grouped differently. This organism is considered an “opportunistic pathogen”, which means that healthy people don’t usually get sick from it, but in a hospital setting with a lot of vulnerable folks, or in people with weaker immune systems, it can cause problems like UTI’s, lung infections, or bloodstream infections. 

The name of this bacterium was changed from Enterobacter aerogenes to Klebsiella aerogenes back in 2017 after new research showed that it is more closely related to Klebsiella species than to other Enterobacter. Scientists found out that its genetics had more in common with Klebsiella pneumoniae, which causes pneumonia, than with the bacteria it had been grouped with before. The scientific community updated the classification, so it better reflects its family. Most more recent studies and textbooks use the updated name Klebsiella aerogenes, but I still saw the older name in some sources. 

https://en.wikipedia.org/wiki/Klebsiella_aerogenes 

https://pmc.ncbi.nlm.nih.gov/articles/PMC9879091/ 

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/enterobacter-aerogenes 

https://emedicine.medscape.com/article/216845-overview 

• Found harmlessly within our gut and the environment

• Considered an opportunistic pathogen, meaning it typically only causes disease in people who are already sick or have a weakened immune system

• Common in hospital acquired infections

Pathogenicity → How It Causes Disease

1. Colonization

• Uses fimbriae to stick to cells and other surfaces [such as catheters]

• Forms biofilms that help the bacteria attach and protects it from antibiotics

• May have a sugary outer layer capsule that helps it stick and survive within the environment

  
  

2. Evasion

• Capsule: Blocks immune cells from recognizing and destroying it

• LPS Outer Membrane: Helps avoid immune attack, can also trigger inflammation within the body

• Siderophores: Special molecules that ‘steal’ iron from the host to help it grow

• Resistance Genes: Can produce beta-lactamases that destroy antibiotics like penicillin. Some strains are even showing resistance to carbapenems which are often ‘last resort’ antibiotics. Gains this resistance through plasmids and gene transfers from other bacteria

  
  

3. Invasion & Spread

• Can enter our bodies if barriers are broken

  • Such as through surgery, placement of indwelling catheters, etc.

• Forms biofilms on medical devices, allowing it to resist treatment and survive longer

• Adapts easily, mutates quickly to acquire new traits that make it more dangerous.

  
  

4. Damage & Symptoms

• Causes tissue damage through the immune systems reaction

• Releases endotoxins from LPS that can lead to fever, inflammation, or even septic shock in severe cases

• Biofilms and capsules can make infection harder to treat leading to chronic symptoms

Common Infections from K. aerogenes:

Urinary Tract Infections [UTIs]

• Symptoms Include: Burning with urination, frequency of urination, cloudy and/or foul smelling urine, lower back pain

Pneumonia

• Symptoms Include: Fever, cough, chest pain, trouble breathing

Sepsis

• Symptoms Include: Fever, chills, confusion, low blood pressure, organ failure

Device Related Infections

• Symptoms Include: Persistent pain and/or swelling near implants or catheters.

Sources:

https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540302/all/Klebsiella%20aerogenes

https://pmc.ncbi.nlm.nih.gov/articles/PMC4435039/

https://pubmed.ncbi.nlm.nih.gov/2857687/

Epidemiology

Found in human GI tract, respiratory tract, and hospital environments

• Transmission:

  -Person to person via contaminated hands or medical equipment.

  -Healthcare-associated infections

• Common Infections:

  -Urinary tract infections

  -Respiratory infections

  -Bloodstream infections

  -Wound infections

• Risk Groups:

-Hospitalized patients

-Immunocompromised individuals

-Patients with invasive devices

Prevention

• Hand Hygiene: Most effective prevention method in healthcare settings.

• Sterile Techniques: Use aseptic methods during insertion of catheters, IVs, etc.

• Isolation Protocols: Use of contact precautions for infected/colonized patients.

• Antibiotic Stewardship: Rational use of antibiotics to prevent resistance development.

Control

• Regular disinfection of hospital surfaces and equipment.

• Track infections and colonization in healthcare settings.

• Monitor for extended-spectrum beta-lactamase (ESBL) or carbapenem-resistant strains (CRE).

• Immediate infection control measures during suspected outbreak.

  
  

https://aeroclave.com/how-to-kill-and-protect-yourself-from-klebsiella-aerogenes/

https://www.cdc.gov/klebsiella/about/index.html

https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/klebsiella.html

https://www.merckmanuals.com/home/infections/bacterial-infections-gram-negative-bacteria/klebsiella-enterobacter-and-serratia-infections

• Contracted through

  • person to person contact

  • contaminated environments like soil and water

  • through contaminated medical devices

  • Wounds caused by injury or surgery

• Most frequently found in the medical field and hospitals

• Spreads through hospitals by the hands of healthcare workers, ventilators, catheters, and contaminated surfaces

• Leads to serious infections in hospital settings or for immunocompromised individuals

  
  

How it's resistance affects patients

• K. aerogenes is recognized for its high pathogenicity and diverse infection routes, leading to a range of serious infections, particularly in immunocompromised individuals, including:

  • Pneumonia

    • K. aerogenes can cause severe respiratory tract infections, particularly hospital-acquired pneumonia and in vulnerable patients on ventilators

  • Urinary tract infections

    • K. aerogenes can cause UTIs, especially in catheterized hospital patients

  • Blood stream infections

    • K. aerogenes can enter the bloodstream and cause bacteremia, which can progress to sepsis or septic shock

  • Wound and surgical infections

    • The bacteria can infect open wounds from injury or surgery, causing complications

      
      

Antibiotic resistance history

• The widespread use of antibiotics has intensified the issue of Klebsiella resistance. Its antibiotic resistance has evolved from Multidrug Resistance (MDR), to Extensively Drug Resistance (XDR), and Pan-Drug Resistance (PDR)

• The resistance rate of Klebsiella to carbapenem antibiotics has significantly increased between 2015 and 2019

• Different species of Klebsiella exhibit species-specific resistance

Antibiotic resistance

• Destroys antibiotics: K. aerogenes acquires genes like blaKPC-2 and blaNDM-1, which encode and produce enzymes called beta-lactamases that break down certain beta-lactam and carbapenems antibiotics

• Pumps them out: It can use tiny cellular "efflux pumps" to remove the antibiotics from inside the cell before they can do damage.

• Blocks entry: The bacteria can alter its outer layer to prevent antibiotics from entering the cell in the first place

• Changes its targets: It can modify the cell parts that the antibiotic is supposed to attack, so the antibiotic can no longer bind to its target

Common antibiotics it's resistant to

• Ampicillin

  • an antibiotic in the penicillin family used to treat bacterial infection

• Amoxicillin

  • a prescription antibiotic in the penicillin family used to treat bacterial infections

• First generation Cephalosporins

  • a class of antibiotics that are effective against a wide range of gram-positive bacteria

• Cefoxitin

  • a second-generation cephamycin antibiotic used to treat and prevent bacterial infections.

Why its antibiotic resistance is an issue

• A doctor may need to use a stronger, less common antibiotic to fight the infection

• The bacteria can become resistant to these "last resort" drugs, making treatment extremely difficult

• The bacterium's ability to acquire genes that give resistance to multiple drugs leads to severe illness and increasing mortality rates

Sources:

https://pmc.ncbi.nlm.nih.gov/articles/PMC11910031/

https://www.nature.com/articles/s41598-024-57245-1

https://pmc.ncbi.nlm.nih.gov/articles/PMC10135309/

https://www.cdc.gov/klebsiella/about/index.html