M. marinum Temperature Growth — SCE Infectious Diseases MCQ

Correct answer: A — The temperature and exposure support Mycobacterium marinum; alert the laboratory because incubation below 37°C is required

The best answer is “The temperature and exposure support Mycobacterium marinum; alert the laboratory because incubation below 37°C is required”. M. marinum is adapted to aquatic environments and cooler tissue, so exposure, sporotrichoid spread and low-temperature culture form a coherent diagnostic pattern. “The organism is Mycobacterium tuberculosis because all acid-fast bacilli grow optimally at 37°C” is less appropriate because it does not satisfy the scenario's decisive clinical or jurisdictional requirement. “The organism is Mycobacterium leprae and should grow on routine mycobacterial culture” is less appropriate because it does not satisfy the scenario's decisive clinical or jurisdictional requirement. “The isolate is Nocardia because photochromogenicity is diagnostic of nocardiosis” is less appropriate because it does not satisfy the scenario's decisive clinical or jurisdictional requirement. “The result is contamination because pathogenic mycobacteria cannot grow below body temperature” is less appropriate because it does not satisfy the scenario's decisive clinical or jurisdictional requirement.

Reference: BTS guideline for non-tuberculous mycobacterial pulmonary disease: https://thorax.bmj.com/content/72/Suppl_2/ii1