A laboratory isolate from a patient with abdominal tuberculosis who consumed unpasteurized dairy products shows rough non-pigmented colonies. Unlike typical human isolates, the organism tests negative for niacin accumulation and nitrate reduction, and shows resistance to pyrazinamide on susceptibility testing. The isolate is:
- A Mycobacterium tuberculosis
- B Mycobacterium bovis ✓
- C Mycobacterium africanum
- D Mycobacterium microti
Correct answer: B. Mycobacterium bovis
Explanation
M. bovis is distinguished biochemically from M. tuberculosis by being niacin negative, nitrate reductase negative, and uniformly resistant to pyrazinamide due to an inherent defect in pncA function. Because of this intrinsic PZA resistance, standard short-course therapy must be modified, usually by adding or extending other agents. Transmission follows ingestion of contaminated milk, producing intestinal, mesenteric nodal, and scrofulodermatous disease rather than classic upper-lobe cavitary pulmonary disease.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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