Antibiotics are categorized into several different classes, each with a different type of effect that inhibits or kills bacteria.
Bacterial cells are prokaryotic; primitive cells that are very different than the eukaryotic cells that make up the human body. The MOA of antibiotics exploits the difference between these cell types so that the drugs harm bacteria without harming our cells.
Antibiotic Modes of Action (MOA) 4/09
The following links will take you to individual articles on each antibiotic class. Each article in this series includes the following information:
- a list of the specific antibiotics that fall in the class (generic and brand names)
- mode of action
- type of infection the antibiotic class to against
- type of bacteria inhibited or killed
- pros and cons of using the class of antibiotics
The main classes of antibiotics include:
Aminoglycosides bind to the bacterial 30S ribosomal subunit, interfering with protein synthesis.
Ribosomes are the protein factory of the cells. They are composed of two subunits, in bacteria a 30S and a larger 50S. By binding to the ribosome, aminoglycosides inhibit the translocation of tRNA during translation and leaving the bacterium unable to synthesize proteins necessary for growth.
2. Beta-lactams (Penicillin and Cephalosporin)
Penicillins and cephalosporins (beta-lactam antibiotics) work by interfering with interpeptide linking of peptidoglycan, the a strong, structural molecule found specifically bacterial cell walls. Cell walls without intact peptidoglycan cross-links are structurally weak, prone to collapse and disintegrate when the bacteria attempts to divide.
3. Macrolides
Macrolides exert their bateriostatic effect by binding irreversibly to the 50S subunit of bacterial ribosomes. Ribosomes are the protein factories of the cell, and by binding to the ribosome, macrolides inhibit translocation of tRNA during translation (the production of proteins under the direction of DNA). Although the cells of humans also have ribosomes, these eukaryotic cellular protein factories differ in size and structure from the ribosomes of prokaryotes.
Broad spectrum synthetic antibiotic that inhibits bacterial DNA replication. Includes nalidixic acid, norfloxacin and ciprofloxacin.
5. Sulfonamides (Sulfa drugs)
Broad spectrum synthetic antibiotic discovered by German chemist Gerhard Domagk in 1935 as the dye Prontosil. Exert action by binding irreversibly to a bacterial enzyme that produces folic acid.
Inhibit bacterial protein synthesis by preventing tRNA molecules from binding to the 30S ribosomal subunit. Representatives of this class include tetracycline, doxycycline and trimocycline.
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Other Microbiology Resources
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Sources
Content
Bauman, R. (2005) Microbiology..
Park Talaro K. (2008) Foundations in Microbiology.
Images
Pill Bottle: WillyWonker Flickr
