Aminoglycosides exert their bactericidal effect primarily by inhibiting which ribosomal subunit?

Explanation

## Aminoglycoside Mechanism of Action **Key Point:** Aminoglycosides irreversibly bind to the **bacterial 30S ribosomal subunit** and inhibit protein synthesis, leading to bactericidal activity (not bacteriostatic). **High-Yield:** Unlike macrolides (50S binders), aminoglycosides target the **30S subunit** of the bacterial 70S ribosome. This binding causes: 1. Misreading of mRNA codons → incorporation of incorrect amino acids 2. Premature termination of translation 3. Formation of aberrant polypeptides 4. **Bactericidal effect** (cell death, not just growth inhibition) **Clinical Pearl:** The bactericidal nature of aminoglycosides is concentration-dependent; higher peak concentrations produce greater killing. This is why once-daily high-dose regimens are preferred over multiple lower doses. **Mnemonic:** **30S = Aminoglycosides** (remember: "30S Starts with Streptomycin, Gentamicin, Amikacin"). Contrast with **50S = Macrolides** (Erythromycin, Azithromycin, Chloramphenicol). | Antibiotic Class | Ribosomal Target | Bactericidal/Static | Mechanism | | --- | --- | --- | --- | | Aminoglycosides | 30S | Bactericidal | Protein synthesis inhibition + misreading | | Macrolides | 50S | Bacteriostatic | Protein synthesis inhibition | | Tetracyclines | 30S | Bacteriostatic | Protein synthesis inhibition | | Chloramphenicol | 50S | Bacteriostatic | Protein synthesis inhibition |