Which Mycobacterium species is recommended to incubate skin cultures for recovery at 30°C?

• A. 22°C
• B. 30°C
• C. 35°C
• D. 42°C

Answer: (B)

Some Mycobacterium species that cause skin infections grow best at cooler temperatures, not at body temperature. Mycobacterium marinum is the classic example; it thrives around 28–30°C and is most readily recovered from skin lesions when cultures are incubated at about 30°C. When incubation is at 37°C or higher, M. marinum grows poorly, which can lead to false negatives. That’s why 30°C is the recommended incubation temperature for skin cultures when M. marinum is suspected. Other temperatures—too cool like 22°C or too warm like 42°C or even 35°C—are less optimal for this organism and reduce the likelihood of successful recovery.