Resistance of Mycobacterium tuberculosis to rifampicin most commonly arises from a mutation affecting which structure?

• A The catalase-peroxidase enzyme encoded by katG
• B The 50S ribosomal protein L22
• C DNA gyrase encoded by gyrA
• D The beta subunit of DNA-dependent RNA polymerase encoded by rpoB ✓

Explanation

Rifampicin binds the beta subunit (rpoB gene product) of bacterial RNA polymerase and blocks transcription initiation by preventing extension of the short RNA chain. Point mutations in a defined region of rpoB alter the drug binding pocket without abolishing enzyme function, producing high-level resistance. katG mutations confer isoniazid resistance, gyrA mutations confer fluoroquinolone resistance, and ribosomal protein changes underlie macrolide resistance.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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