The etiologic agent of 'swimming pool granuloma' is which Mycobacterium?

• A. M. fortuitum
• B. M. kansasii
• C. M. marinum
• D. M. xenopi

Answer: (C)

Swimming pool granuloma is a infection of the skin caused by Mycobacterium marinum, a slow-growing nontuberculous mycobacterium that thrives in aquatic environments. It tends to produce chronic granulomatous skin lesions after minor skin trauma exposed to water, especially around fish tanks or swimming pools. It grows best at cooler temperatures (around 30°C), which explains why the infection is cutaneous rather than deep-seated or pulmonary. The other bacteria listed are associated with different disease patterns: rapid-growing mycobacteria commonly cause wound or hardware infections, and the remaining species are more often linked to pulmonary disease in humans.