Which Mycobacterium grows only at 35°C and is differentiated from other mycobacteria by its susceptibility to T2H?

Which Mycobacterium grows only at 35°C and is differentiated from other mycobacteria by its susceptibility to T2H?

• A. M. kansasii
• B. M. avium-intracellulare complex
• C. M. bovis
• D. M. tuberculosis

Answer: (C)

Differentiating closely related mycobacteria often uses two practical clues: where they grow and how they respond to a selective chemical. The organism in question prefers a cooler growth temperature, functioning well at around 35°C, and it is inhibited by thiophene-2-carboxylic hydrazide (TCH) on testing. This combination points to Mycobacterium bovis, which grows best at 35°C and shows susceptibility to TCH, setting it apart from other members of the M. tuberculosis complex. In contrast, the typical tuberculosis pathogen grows best at 37°C and is not inhibited by TCH, so the temperature preference plus TCH susceptibility together help distinguish M. bovis from M. tuberculosis and related species.