Mycobacterium marinum
David Calcara

Mycobacterium marinum was first isolated from salt water fish in 1926 by JD Aronson. Like other organisms in the genus Mycobacterium, it is a rod-shaped, gram-positive bacteria. It is a facultative anaerobe and can be grow autotrophically on only carbon dioxide and hydrogen gas. It is most commonly free-living in both salt and fresh water, but will infect fish and occasionally humans. It is classified as a slow-growing Non Tuberculosis Mycobacterium (NTM), and thus was relatively ignored after its discovery.

Mycobacterium marinum was originally thought to only be a fish parasite. It wasn’t until the early 1950s that it was discovered to cause disease in humans as well. It causes what is commonly known as Swimming Pool Granuloma and is characterized by skin lesions on the elbows, knees, hands and feet. Because of the bacteria’s slow growing nature, the symptoms can last 2 to 4 months or longer. It is treated with antibiotics which must be taken for at least 6 months. A M. marinum infection can be severe for people with immune system problems and possibly, although very rarely, cause death. An infection is easily prevented by staying away from contaminated water, wearing gloves during, and thoroughly cleaning hands after, cleaning a fish tank, and avoiding infected fish.

Mycobacterium marinum is closely related of M. tuberculosis, the bacterium that causes the severe lung infection tuberculosis. Cases of this dreaded disease are skyrocketing after a long, seemingly dormant period and many common strains are very resistant to today’s best antibiotics. This had led to a call for a tuberculosis vaccine, but creating one has proved very difficult. This problem has led one researcher, Michele Trucksis from the University of Maryland medical school, to look for mutant strains of M. marinum with the hope of developing such a vaccine. In the process they also hope to create a vaccine against M. marinum to protect fish from a disease that can cripple fish farms and aquariums.

Trucksis works with goldfish trying to find mutants and identify the genes that assist in virulence. Virulence is the trait that allows a pathogen to fight its host’s defenses and cause an infection. So far she has identified 10 genes involved in virulence, including one gene possible regulatory gene that controls all the virulence genes. All of these genes seem to have recognizable counterparts in M. tuberculosis. The next step in this research would be to try to discover how these genes worked and try to find a way to disrupt their function. If she is able to do this and successfully create a vaccine for tuberculosis, then she will help eradicate a very dangerous disease world wide.


Aronson, J. D. 1926. Spontaneous tuberculosis in salt water fish. J Infect Dis 39:314-320

A Real Fish Story found on

Mycobacterium from

Mycobacterium marinum Fact Sheet from the Maryland Department of Health & Mental Hygiene, Epidemiology & Disease Control Program.

Swimming Pool Granuloma from

The Prokaryotes, 2nd ed. Editors: Albert Ballows, et. al.

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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