Which statement is correct regarding differentiating M. bovis from M. tuberculosis?

• A. Niacin production (negative in M. bovis)
• B. Growth at 42°C
• C. Resistance to PPD
• D. Catalase activity

Answer: (A)

Differentiating M. bovis from M. tuberculosis relies on a simple biochemical difference: niacin production. M. tuberculosis synthesizes and releases niacin during growth, giving a positive niacin test, while M. bovis does not produce niacin, yielding a negative result. This makes the statement that niacin production is negative in M. bovis the best differentiator because it cleanly separates the two in the lab. Other features aren’t reliable discriminators here: growth at a higher temperature like 42°C isn’t a consistent differentiate between these two, resistance to PPD isn’t a bacterial property used for species differentiation since PPD is a host diagnostic reagent, and catalase activity isn’t specific enough to distinguish M. bovis from M. tuberculosis.