Which biochemical property reliably separates Mycobacterium tuberculosis (human variant) from Mycobacterium bovis in the laboratory?

• A Positive catalase and positive urease in M. bovis
• B Positive nitrate reduction test and positive niacin accumulation test in M. tuberculosis ✓
• C Growth on media containing glycerol in M. bovis
• D Positive Tween 80 hydrolysis in M. tuberculosis

Explanation

The human tubercle bacillus accumulates free niacin in the medium (positive niacin test) and reduces nitrate to nitrite, whereas M. bovis is negative for both. M. tuberculosis also thrives on glycerol-containing media while M. bovis prefers pyruvate, making option C backwards. Both organisms are strongly catalase positive, and neither shows Tween 80 hydrolysis, so those options fail to discriminate.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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