Which species is a photochromogenic mycobacterium that grows at approximately 30°C?

Which species is a photochromogenic mycobacterium that grows at approximately 30°C?

• A. Mycobacterium marinum
• B. Mycobacterium kansasii
• C. Mycobacterium tuberculosis
• D. Mycobacterium smegmatis

Answer: (A)

Photochromogenic mycobacteria develop pigment after exposure to light, and they often prefer cooler growth temperatures around 25–32°C. M. marinum is the classic example that fits this combination: it produces pigment when illuminated and grows best near 30°C. It’s frequently encountered in aquatic environments and can cause skin infections after aquatic exposure, which fits the clue of a cooler-temperature, light-induced pigment producer. The other organisms don’t fit the exact clue as neatly. Tuberculosis bacteria grow best at body temperature (around 37°C) and are not pigmented in light. A rapid grower like M. smegmatis is typically nonpigmented and grows quickly at higher temperatures. While M. kansasii is a slow-growing, photochromogenic species, the specific hint of growth around 30°C is most characteristic of M. marinum.

Photochromogenic mycobacteria develop pigment after exposure to light, and they often prefer cooler growth temperatures around 25–32°C. M. marinum is the classic example that fits this combination: it produces pigment when illuminated and grows best near 30°C. It’s frequently encountered in aquatic environments and can cause skin infections after aquatic exposure, which fits the clue of a cooler-temperature, light-induced pigment producer.

The other organisms don’t fit the exact clue as neatly. Tuberculosis bacteria grow best at body temperature (around 37°C) and are not pigmented in light. A rapid grower like M. smegmatis is typically nonpigmented and grows quickly at higher temperatures. While M. kansasii is a slow-growing, photochromogenic species, the specific hint of growth around 30°C is most characteristic of M. marinum.