Antibiotics Classes to Know for Microbiology

Antibiotics are crucial in fighting bacterial infections, each class targeting specific bacterial functions. Understanding these classes helps us appreciate their roles in microbiology and the challenges posed by antibiotic resistance in treating infections effectively.

1. Beta-lactams (Penicillins, Cephalosporins, Carbapenems)

   • Inhibit bacterial cell wall synthesis, leading to cell lysis and death.
   • Penicillins are effective against Gram-positive bacteria; cephalosporins have a broader spectrum.
   • Carbapenems are reserved for multi-drug resistant infections due to their broad activity.
   • Resistance mechanisms include beta-lactamase production by bacteria.

2. Aminoglycosides

   • Inhibit protein synthesis by binding to the 30S ribosomal subunit.
   • Effective against aerobic Gram-negative bacteria and some Gram-positive bacteria.
   • Often used in combination with other antibiotics for synergistic effects.
   • Nephrotoxicity and ototoxicity are significant side effects.

3. Tetracyclines

   • Inhibit protein synthesis by binding to the 30S ribosomal subunit.
   • Broad-spectrum antibiotics effective against a variety of bacteria, including atypical pathogens.
   • Can cause photosensitivity and should not be used in children or pregnant women due to effects on bone and teeth.
   • Resistance is common due to efflux pumps and ribosomal protection.

4. Macrolides

   • Inhibit protein synthesis by binding to the 50S ribosomal subunit.
   • Effective against Gram-positive bacteria and some Gram-negative bacteria, as well as atypical pathogens.
   • Commonly used for respiratory infections and in patients with penicillin allergies.
   • Can cause gastrointestinal side effects and have potential drug interactions.

5. Fluoroquinolones

   • Inhibit bacterial DNA gyrase and topoisomerase IV, disrupting DNA replication.
   • Broad-spectrum activity against both Gram-positive and Gram-negative bacteria.
   • Associated with tendonitis and tendon rupture, particularly in older adults.
   • Resistance can develop through mutations in target enzymes.

6. Sulfonamides

   • Inhibit bacterial folic acid synthesis by blocking the enzyme dihydropteroate synthase.
   • Effective against a range of Gram-positive and Gram-negative bacteria.
   • Often used in combination with trimethoprim (as TMP-SMX) for enhanced efficacy.
   • Can cause allergic reactions and hematological side effects.

7. Glycopeptides (e.g., Vancomycin)

   • Inhibit bacterial cell wall synthesis by binding to D-alanyl-D-alanine precursors.
   • Primarily effective against Gram-positive bacteria, including MRSA.
   • Used for serious infections when beta-lactams are not effective.
   • Can cause nephrotoxicity and "red man syndrome" if infused too rapidly.

8. Oxazolidinones (e.g., Linezolid)

   • Inhibit protein synthesis by binding to the 50S ribosomal subunit and preventing formation of the initiation complex.
   • Effective against Gram-positive bacteria, including resistant strains like MRSA and VRE.
   • Can cause myelosuppression and peripheral neuropathy with prolonged use.
   • Interactions with monoamine oxidase inhibitors (MAOIs) can lead to serotonin syndrome.

9. Polymyxins

   • Disrupt bacterial cell membrane integrity, leading to cell death.
   • Primarily effective against Gram-negative bacteria, including multidrug-resistant strains.
   • Used as a last resort due to nephrotoxicity and neurotoxicity.
   • Resistance is emerging, limiting their clinical utility.

10. Nitroimidazoles (e.g., Metronidazole)

    • Disrupt DNA synthesis and function in anaerobic bacteria and protozoa.
    • Effective against anaerobic infections and certain protozoal infections (e.g., Giardia).
    • Can cause gastrointestinal side effects and a disulfiram-like reaction with alcohol.
    • Resistance is less common but can occur, particularly in certain anaerobic bacteria.