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Anti - bacterial range of various classes of drugs

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Anti - bacterial range of various classes of drugs

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Tetracyclines have a broad spectrum of antibiotic action

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Resistance amongst Staphylococcus spp., Streptococcus spp., Neisseria gonorrhoeae, anaerobes, members of the Enterobacteriaceae and several other previously sensitive organisms is now quite common.Minocycline is also effective against N. meningitidis. However, many strains have become resistant to the drug, thereby decreasing its usefulness.
Thus, most common mechanism for gram-negative bacterial resistance was found to be insertion of a plasmid-encoded active-efflux pump that translocates tetracycline out of the cell.
While mechanism for gram-positive bacterial resistance may be either through this active efflux mechanism or through changes in its ribosomal target.
Thus, three mechanisms for resistance have been reported:

decreased intracellular concentration by decreased influx or increased efflux

decreased tetracycline ribosomal binding

enzymic inactivation of tetracycline

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Tetracyclines are bacteriostatic in nature.

These drugs hold a very wide range of spectrum that includes gram-positive and gram-negative bacteria with a few exceptions such as, Pseudomonas aeruginosa and Proteus spp., that display intrinsic resistance. However, acquired resistance has proliferated in many pathogenic organisms and greatly eroded the formerly vast versatility of this group of antibiotics.

These agents remain especially useful in the management of infections by certain obligately intracellular bacterial pathogens such as Chlamydia, Mycoplasma and Rickettsia.

They are also of value in spirochaetal infections, such as syphilis, leptospirosis and Lyme disease.

Certain rare or exotic infections, including anthrax, plague and brucellosis, are also susceptible to tetracyclines.

These agents also have also been reported to have activity against certain eukaryotic parasites, including those responsible for diseases such as malaria and balantidiasis.

The following represents MIC susceptibility data for a few medically significant microorganisms:
1) Escherichia coli: 1 μg/mL — >128 μg/mL
2) Shigella spp.: 1 μg/mL — 128 μg/mL

Originally all types of organisms except viruses and fungi.

Bacteriostatic activity is found against:
a) Cocci: All +ve and –ve cocci such as S. pneumoniae, gonococi, meningitidis are sensitive. Resistance developed to S. aureus, pyrogens and enterococci
b) Bacilli (+ve): Clostridia, listeria, anthracis etc, but not Mycobacteria
c) Bacilli (-ve): Cholerae, Y. pestis, Helicobacter, Brucella etc. but H. Influenzae become insensitive
d) Enterobacteriocae: Resistant and not effective against  Pseudomonas, Klebsiella and Salmonella.
e)  Enterococci: Histolytica and plasmodia
f) Misc: Spirochaetes (T. pallidum, Borrelia), All rickettsiae, chlamidiae, mycoplasma and actinomycetes etc.

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This antibiotic tutorial explains the mode of action of tetracycline antibiotics. It also explains the use and side effects of tetracycline in antibacterial treatment. For more information, log on to- http://shomusbiology.weebly.com/ Download the study materials here- http://shomusbiology.weebly.com/bio-materials.html