A culture isolate from a cattle farmer with pulmonary disease resembles Mycobacterium tuberculosis morphologically. Which combination of biochemical properties best distinguishes Mycobacterium bovis from M. tuberculosis?
- A Niacin negative, nitrate reductase negative ✓
- B Niacin positive, nitrate reductase positive
- C Catalase negative, urease positive
- D Niacin positive, pyrazinamide susceptible
Correct answer: A. Niacin negative, nitrate reductase negative
Explanation
Mycobacterium bovis is niacin-negative and does not reduce nitrate, whereas M. tuberculosis is typically niacin-positive and strongly nitrate-reductase positive. B further clinically important difference is that M. bovis is inherently resistant to pyrazinamide, so treatment regimens omit this drug. Option D is wrong because niacin positivity with pyrazinamide susceptibility describes M. tuberculosis itself.
Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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