Resistance to ethambutol in Mycobacterium tuberculosis most commonly arises from mutations affecting which structure?

• A The embB gene encoding arabinosyltransferase ✓
• B The rpoB gene encoding RNA polymerase
• C The pncA gene encoding pyrazinamidase
• D The gyrA gene encoding DNA gyrase

Explanation

Ethambutol targets arabinosyltransferase encoded by embB, and mutations in this gene confer resistance by altering drug binding at the arabinan polymerisation site. The other options are distractors drawn from sister drugs: rpoB mutations cause rifampicin resistance, pncA loss causes pyrazinamide resistance, and gyrA mutations cause fluoroquinolone resistance.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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