Mycobacterium marinum

Mycobacterium marinum is pathogenic for fish and other aquatic animals (crustaceans, amphibias, …). Transmission to man results from cutaneous lesions in contact with infected animals or waters (aquariums, swimming-pools, lakes, rivers). Clinical manifestations evolve relatively slowly and are mainly skin infections. They consist of papulo-nodules which may evolve towards ulceration. The main extra-cutaneous extension is adenopathy of the satellite lymphnode. More rarely sites have been described such as tenosynovitis, joint and bone infections. The usual treatment consists of a monotherapy with clarithromycin, minocyclin or doxycycline or the association rifampin-ethambutol for 3 months. In HIV positive patients, the use of antibiotic association including clarithromycin is recommended for a minimum of 6 months. Identification relies on the rapid growth of colonies in 5 days and their photochromogenicity. If M. marinum is suspected, incubation must be maintained at 30°C for 2 months before scoring a negative culture. The genetic proximity of M. marinum and M. ulcerans, agent of chronic skin ulcers, has been demonstrated. Phylogenetic studies suggest that M. marinum and tubercle bacilli diverge from a common ancestor and use similar strategies for replication in macrophages and persistence in granulomas.