Streptomycin, used in TB treatment, belongs to which antibiotic class and acts by what mechanism?
- A Aminoglycoside; binds 50S ribosomal subunit blocking peptide bond formation
- B Aminoglycoside; binds 30S ribosomal subunit causing misreading of mRNA ✓
- C Macrolide; binds 50S ribosomal subunit blocking translocation
- D Polymyxin; disrupts mycobacterial cell membrane integrity
Correct answer: B. Aminoglycoside; binds 30S ribosomal subunit causing misreading of mRNA
Explanation
Streptomycin is an aminoglycoside that binds irreversibly to the 16S rRNA of the 30S ribosomal subunit, causing misreading of mRNA and producing truncated, non-functional proteins. It requires oxygen-dependent active transport, explaining its lack of activity against anaerobes. It is bactericidal against extracellular TB bacilli only. Resistance arises from rrs (16S rRNA) or rpsL (ribosomal protein S12) mutations.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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