An aminoglycoside such as gentamicin is bactericidal against aerobic Gram-negative bacilli. Its primary lethal mechanism at the ribosomal level is:

• A Binding the 30S subunit and blocking aminoacyl-tRNA entry into the A site
• B Preventing dissociation of the 70S ribosome after chain termination
• C Blocking peptidyl transferase on the 50S subunit
• D Binding the 30S subunit and inducing misreading of mRNA codons ✓

Explanation

Aminoglycosides bind the 30S ribosomal subunit near the decoding region, causing misreading of codons so wrong amino acids are incorporated into growing peptides, producing nonfunctional proteins and bacterial death. Option A describes tetracyclines, which block tRNA binding but are only bacteriostatic. Option C describes chloramphenicol and lincosamides acting on the 50S subunit. The bactericidal action depends on oxygen-dependent active uptake, explaining their inactivity against anaerobes.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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