Mycobacterium marinum

Non-tuberculous mycobacterium found in salt and fresh water.

M. marinum is the etiologic agent in swimming pool granuloma and is isolated exclusively from superficial lesions or affected lymph nodes (Petrini B 2006). Typically, patients have contact with aquaria. Infections with this germ are also described as a consequence of therapies with biologics (Ferreira J et al. 2012; Kump PK et al. 2013). M. marinum grows preferentially at 31 °C. Photochromogenicity is a characteristic feature. It should be noted that IGRA tests may be positive here, as with M. kansasii, M. flavescens, and M. szulgai, and thus are not suitable for ruling out tuberculosis (Lalvani A et al. 2008).

Slow-growing, aerobic, acid-fast rod that thrives primarily at about 26-33 °C (optimum 31-32 °C) in humid environments. Infected fish and snails contaminate fresh and salt water. Occurs also in insufficiently chlorinated swimming pools.

No transmission from person to person. Infections often occur during contact with aquariums, fish breeding tanks or fish tanks, swimming in contaminated waters, swimming pools or whirlpools, and handling infected fish or seafood (fish processing).

Infection usually via previously damaged skin. At the site of injury (e.g. back of the hand, fingers, lower leg, toes), individual, livid or brownish-red, indurated, 0.5-3 cm large, not infrequently painful papules or nodules with a verrucous surface develop after an incubation period of 2-4 weeks. Subsequent superficial ulceration and crusting. Rarely secondary involvement of the draining lymphatic ducts (sporotrichoid course along the lymphatic ducts). Occurs frequently in immunosuppressed patients.

See also swimming pool granuloma.

Resistance testing shows resistance to INH and sensitivity to EMB, RMP, and clarithromycin for M. marinum. For infections with M. marinum, a two-drug combination with clarithromycin and RMP for several months is recommended, depending on the granuloma extent and healing process (four months or more) (Aubry A et al. 2002). Therapy can probably be optimized by the addition of EMB through the synergistic effect with RMP. Combinations of clarithromycin and EMB and of RMP and EMB have also been reported to be well effective. Furthermore, minocycline, doxycycline, and trimethoprim/sulfmethoxazole can also be used (Griffith DE et al. 2007). For deeper skin and soft tissue infections caused by M. marinum, surgical intervention (debridement) may be indicated, but only in combination with drug treatment.

Avoid bathing activities in case of superficial skin injuries, or cover with sterile and waterproof bandages before being in the water.

Wear waterproof protective gloves when working in aquariums, fish tanks or fish processing.

Sufficient chlorination of swimming pools.

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