(formerly M. balnei
) is a free-living bacterium
, which causes opportunistic infections
in humans. Although Aronson isolated this mycobacterium
in 1926 from a fish, it was not until 1951 that it was found to be the cause of human disease by Linell and Norden. Large outbreaks of infection due to this atypical mycobacterium have been described in association with swimming (69). Infections related to swimming pools have now drastically fallen due to the improvements in the construction and maintenance of these facilities (70).
The first case of M. marinum infection associated with a fish-tank (‘fish-tank granuloma) (71) was reported in 1962 by Swift and Cohen (72). M. marinum infection may be an occupational hazard for certain professions such as pet shop workers, but most infections occur in fish fanciers who keep an aquarium at home (73). Although infection may be caused by direct injury from the fish fins or bites (74), most are acquired during the handling of the aquariums such as cleaning or changing the water. Indirect infection has also been described related to a child’s bathing utensils that had been used to clean a fish tank (75).Due to an increased awareness of the disease and improved isolation methods, more and more cases are being recognized and reported worldwide (76).
Skin lesions produced by M. marinum
infections may be single but are often multiple. Typically, clusters of superficial nodules or papules are described. An erythematous plaque has also been reported. The lesions may be painful or painless and may become fluctuant. The lesions typically occur on the elbows, knees and feet in swimming pool-related cases, and on the hands and fingers in aquarium owners. The inhibition of growth of M. marinum
at 37°C is related to its ability to infect the cooler parts of the body especially the extremities. Lesions appear after an incubation period of about 2-4 weeks, and after 3-5 weeks they are typically 1-2.5 cm in diameter. Although most infections follow an indolent
course, the disease can progress rapidly (77). Rarely, disseminated infection and bacteremia has been reported in immunocompromised
Diagnosis is frequently delayed, probably due to the rarity of the infection and a failure to elicit the usual history of aquatic exposure. Common misdiagnosis include fungal and parasitic infection, cellulitis, skin tuberculosis
, rheumatoid arthritis
, foreign body reaction and a skin tumor (73). A high index of suspicion and a detailed history are important in establishing the diagnosis of M. marinum
infection. Long delays in diagnosis can result in severe, destructive infection. On primary isolation M. marinum
grows on LJ slants at 30-33°C in 7-21 days (79). Unlike M. tuberculosis
, most strains of M. marinum
will not grow at the usual incubation temperature of 37°C. Colonies are cream in color and turn yellow when exposed to light (photochromogenic
). M. marinum
, once cultured, is readily identified by using conventional mycobacterial characterization methods. It grows relatively quickly (1 to 2 weeks) and is easily recognized as a result of its photochromogenicity. Infections due to M. marinum
can usually be treated with antimycobacterial drugs. Sometimes, cultures are negative but the diagnosis is still made based on physical signs supported by typical histological findings, as M. marinum
is a very common atypical mycobacterium causing skin infection (70). Various DNA-based techniques have been used to classify mycobacteria (80) (55) (81) (47). All such studies have demonstrated a high taxonomic affiliation between M. ulcerans
and M. marinum
. Some M. marinum
isolates have been shown to harbor the insertion sequence, IS2404
, however, no M. marinum
strains contain IS2606
. M. ulcerans
isolates are positive for both insertion sequences. It was previously thought that IS2404
were specific to M. ulcerans
but recent evidence has proved this true only for IS2606
The management of M. marinum infections depends on the severity of the infection. A prolonged course of antibiotic therapy is curative in most superficial cases but adjunctive surgical intervention is sometimes indicated in extensive and deep infections.
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From: Master Thesis presented at the Master Program in Medical and Pharmaceutical Research
Vrije Universiteit Brussel, Brussels, Belgium. Genotyping Mycobacterium ulcerans, M. marinum and M. liflandi using mycobacterial interspersed repetitive units, and gyrase restriction enzyme analysis. Pieter Stragier. 2003 – 2004