Mycobacterium marinum infection

Mycobacterium marinum causes localised papular or nodular skin lesions following exposure to fresh or salt water (fish-tank or swimming-pool granuloma). Diagnosis is often made by biopsy. Consider sporotrichosis (a lymphocutaneous infection caused by Sporothrix schenckii) as a differential diagnosis.

Seek expert advice about the management of M. marinum infection. Antibiotic therapy is not required if a single lesion is successfully excised.

There are no randomised controlled trials comparing treatment regimens. A number of drugs have in vitro efficacy, including clarithromycin, ethambutol, rifampicin, doxycycline, trimethoprim+sulfamethoxazole and moxifloxacin; these are often used in combination. The optimal duration of therapy is not known, but treatment is recommended for 1 to 2 months after the resolution of all lesions (typically 3 to 4 months in total). Perform susceptibility testing if treatment failure occurs.

Surgical excision or debridement (especially for closed spaces of the hand) may be indicated.