Mycobacterium marinum infection.

A 64-year-old man presented for evaluation of tender pustules that developed on his right hand and subsequently spread up his arms in a sporotrichoid manner. Owing to the prominent history of recent trauma followed by fish tank exposure, the patient was started on doxycycline for coverage of Mycobacterium marinum. Subsequent tissue culture grew M. marinum and confirmed the clinical diagnosis. M. marinum is an atypical mycobacteria that is ubiquitously found in aquatic environments. Owing to its optimal growth temperature of 25 to 35 degrees C, infections in humans are mostly restricted to the skin. Furthermore, the organism can spread by lymphatic drainage leading to the clinical appearance of sporotrichoid lesions. The preferred treatment for M. marinum is doxycycline, which was started in our patient and has subsequently improved his clinical condition.