Mycobacterium marinum, the causative agent of fish tank or swimming pool granuloma, is an atypical mycobacterial skin infection often contracted from contaminated fish tanks, swimming pools, and ocean and lake water. It is found in both fresh- and saltwater environments. Minor trauma is a predisposing factor. Aquarium enthusiasts and fish and seafood market workers are usually not aware of the risk of infection. Because of occupational risks (eg, fisherman), men are more commonly affected than women.

The typical skin lesion consists of a pustule or nodule and develops on an extremity 2-3 weeks after exposure. Nodules may ulcerate, suppurate, and spread via lymphangitic spread (about 25% of cases). In more severe infections, deeper manifestations such as tenosynovitis, arthritis, bursitis, or osteomyelitis may be seen. In immunosuppressed patients, disease can disseminate to the lungs or other systems; bacteremia is rare.

In general, the infection is usually mild and self-limited, and lesions may heal over a period of 1-2 years if left untreated, although treatment is recommended.

Related topics: Mycobacterium avium-intracellulare, Mycobacterium kansasii, Mycobacterium fortuitum, Mycobacterium chelonae, Mycobacterium scrofulaceum, Mycobacterium tuberculosis, and Atypical mycobacterial infections