A 6-year-old boy who regularly consumes unpasteurised milk from his family's cattle presents with chronic mesenteric lymphadenitis and low-grade fever. Culture of the node aspirate yields a slow-growing acid-fast bacillus that is niacin negative and nitrate reductase negative. The drug to which this organism is characteristically naturally resistant is:
- A Pyrazinamide ✓
- B Isoniazid
- C Rifampicin
- D Ethambutol
Correct answer: A. Pyrazinamide
Explanation
Mycobacterium bovis, acquired by ingestion of contaminated milk, causes intestinal and mesenteric lymph node tuberculosis in children. It is niacin negative and nitrate negative, unlike human M. tuberculosis. M. bovis lacks pyrazinamidase activity and is inherently resistant to pyrazinamide, so standard short-course regimens must substitute another drug. It remains fully susceptible to rifampicin, isoniazid and ethambutol.
Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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