Mycobacterium marinum is the most common atypical mycobacterium that can cause infections in humans. It is found in both fresh and salt water, and is classified as an acid-fast bacilli. It may cause skin and soft tissue infection after skin abrasions. The patients are usually exposed to aquatic environments, such as aquariums and swimming pools, which is why this disease often occurs following the cleaning of fish tanks. The bacilli enter the body through scratches and abrasions of the skin, causing lesions in the tissue. The wrist and the hand are the most commonly affected areas, and occur in about 50% of cases.
The diagnosis of a Mycobacterium marinum infection is usually delayed, because the condition is rare and the history of aquatic exposure is often not obtained. However, to diagnose, the clinical findings would include involvement of the hand and wrist, painful swelling about the hand, subcutaneous granules, masses, nodules, ulcers, and noncaseating granulomas, symptoms like chronic tenosynovitis of the hand, and the extensors are affected more than the flexors of the hand.
This bacteria can cause a tuberculosis-type infection in fish, and is therefore is called fish tuberculosis. In humans, the chronic skin lesion is sometimes called a “swimming pool granuloma” or “fish tank granuloma”, due to the fact the bacterium is often picked up in these locations.
The bacteria grows in low temperature cultures at 30 degrees centigrade. It grows on Lowenstein-Jensen mediums, and requires a lower temperature and longer period of intubation, up to six weeks or more.
To treat the Mycobacterium marinum, oral antibiotics antimicrobial therapy is used. Ethambutol and Rifampin are used if diagnosed early. Minocycline and Clarithromycin have also been used. If the infection is detected later, however, surgery may need to be done. Surgery is performed for deep infections, which can occur if the infection is not treated early. Surgery to treat this infection entails a synovectomy and debridement, in addition to oral antibiotics for approximately 3 months.
Another entity of atypical microbacterium is called Mycobacterium avium- intracellulare. This type typically occurs in terminal AIDS patients, but can also occur in a non HIV patient.
