Skin cultures for the recovery of Mycobacterium spp. should be incubated at

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

Answer: (B)

Different Mycobacterium species have different optimal growth temperatures, and the environmental mycobacteria that commonly cause skin infections prefer cooler conditions. Incubating skin specimens at about 30°C provides the best environment for these organisms to multiply, increasing the chance of recovery. Higher temperatures, such as 37°C, favor other mycobacteria (like the tuberculosis complex) and may reduce recovery of the cutaneous, environmental types. Cooler temperatures like 22°C are often too low for robust growth of many mycobacteria, while 42°C is well above their tolerance. Therefore, 30°C is the best choice for isolating Mycobacterium spp. from skin specimens.