Microbiology · MU Sofia

20. Antibacterial Agents - Protein and Nucleic acids Synthesis inhibitors, mechanism of action and resistance

Covers bacterial protein synthesis inhibitors by ribosomal subunit target, including aminoglycosides, tetracyclines, macrolides, lincosamides, chloramphenicol and mupirocin, with their mechanisms, spectra and adverse effects. It then turns to nucleic acid synthesis inhibitors such as quinolones, rifamycins and metronidazole, and closes with the resistance mechanisms for each group. A summary table compares targets, mechanisms, resistance and side effects across the agents.

Inside: 3 sections · 1 table · 15 flashcards · 6 min

Topic 20 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 3 sections, about 705 words (6 min of reading), with 15 flashcards.

In this note

  1. Antibacterial Agents - Protein and Nucleic acids Synthesis inhibitors, mechanism of action and resistance
  2. Inhibitors of Bacterial Protein Synthesis
  3. Inhibitors of Bacterial Nucleic Acid Synthesis

Inhibitors of Bacterial Protein Synthesis

These antibacterial agents primarily target the bacterial ribosome, specifically the 70S ribosome, which is composed of 50S and 30S subunits. This is a key target because bacterial ribosomes differ structurally from mammalian ribosomes (which are 80S), providing a basis for selective toxicity.

  • Mechanism of Action:
  • Disrupt bacterial protein synthesis by binding to either the 30S or 50S ribosomal subunit, interfering with processes like tRNA binding or polypeptide elongation.
  • Activity can be bacteriostatic (reversibly inhibiting growth) or bactericidal (irreversibly killing), depending on the drug, concentration, and organism.
  • Targets and Examples:
  • Bind to 30S Ribosomal Subunit:
  • Aminoglycosides:
  • Mechanism: Bind to the 30S subunit. They are generally bactericidal.
  • Spectrum/Usage: Broad spectrum, used for serious infections caused by Gram-negative bacteria and some Gram-positive bacteria. They are typically inactive against anaerobes and Streptococci.
  • Examples: Streptomycin, Gentamicin, Amikacin, Tobramycin, Netilmicin, Sisomicin, Kanamycin, Neomycin. Neomycin and paramomycin are mainly for oral or topical use.
  • Adverse Effects: Significant nephrotoxicity and ototoxicity.
  • Tetracyclines:
  • Mechanism: Bind reversibly to the 30S ribosomal subunit, blocking the binding of aminoacyl-tRNA. They are primarily bacteriostatic.
  • Spectrum/Usage: Broad spectrum. Effective against infections caused by Chlamydia, Mycoplasma, and Rickettsia. Also used for conditions like acne or respiratory infections.
  • Examples: Tetracycline, Doxycycline, Chlortetracycline, Oxytetracycline.
  • Considerations: Contraindicated in children under 8 years old due to potential bone and tooth damage.
  • Bind to 50S Ribosomal Subunit:
  • Macrolides:
  • Mechanism: Bind to the 50S ribosomal subunit, inhibiting the elongation of the polypeptide chain. They are generally bacteriostatic. High doses can be bactericidal.
  • Spectrum/Usage: Broad spectrum, effective against Gram-positive cocci, Mycoplasma, Legionella, Chlamydia, and Campylobacter. Can be an alternative for Gram-positive infections in penicillin-allergic patients.
  • Examples: Erythromycin, Clarithromycin, Azithromycin, Roxithromycin.
  • Adverse Effects: Gastrointestinal disturbances, hepatotoxicity.
  • Lincosamides:
  • Mechanism: Bind to the 50S ribosomal subunit, inhibiting protein synthesis, similar to macrolides. They are bacteriostatic.
  • Spectrum/Usage: Primarily effective against Gram-positive cocci and Anaerobes. Can be an alternative for patients allergic to penicillin.
  • Examples: Clindamycin, Lincomycin.
  • Adverse Effects: Gastrointestinal disturbances, notably pseudomembranous enterocolitis (due to Clostridium difficile infection).
  • Chloramphenicol:
  • Mechanism: Binds to the 50S ribosomal subunit, preventing peptide bond formation. It is a bacteriostatic antibiotic.
  • Spectrum/Usage: Broad spectrum. Used for serious infections like meningitis, plague, cholera, and typhoid fever. Can be used topically as an eye ointment.
  • Adverse Effects: Significant toxicity, including bone marrow suppression which can lead to aplastic anemia, and "Gray baby" syndrome in neonates. Reduced uptake is a mechanism of resistance.
  • Other Protein Synthesis Inhibitor:
  • Mupirocin:

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