As I was reading articles on the Tropical Fish Hobbyist website, I like keeping fish weird I know, I came across an interesting article. I have had many different fish over the years ranging from simple freshwater fish, to jellyfish or lion fish but I have never heard of Mycobacterium in aquariums! Mycobacteria usually are not pathogenic to humans, except for a few such as tuberculosis and leprosy, so this was an interesting find since some of us are working with mycobacteria. M. marinum can be found in any type of tank (freshwater, saltwater, and brackish) but luckily are rare infections to contract.

M. marinum infections can be pretty difficult to diagnose considering that there are few doctors that know about the various infections originating in the aquarium; also the fact that M. marinum has an incubation period of four weeks doesn’t help. The bacteria gains entry into the body by small cuts that are exposed to the infected water. Once inside the bacteria are quickly phagocytosed by macrophages, such phagocytosed material is normally degraded in lysosomes; however, mycobacteria resist lysosomal degradation and somehow manage to survive and even multiply within macrophage phagosomes!  In an effort to contain the infection these macrophages clump together to form granulomas, which are mainly found on the superficial layers of the skin in an M. marinum infection.The bacteria gains entry into the macrophages via receptor mediated phagocytosis and certain plasma membrane cholesterol recognition. Certain antibiotics deprive the macrophages of this cholesterol so that the mycobacteria have no means of entry. This inhibition of uptake is specific for mycobacteria, as other microorganisms can still enter cholesterol-depleted macrophages.

This bacterial infection isn’t as virulent as tuberculosis, but can be pretty annoying as it can persist for one hundred and sixty days on average! So next time when you’re fumbling around in you’re aquarium, hopefully I am not the only one who does, look for cuts on your hands before putting them in the tank, or else you might contract a mycobacteria infection! Just thought you’d like to know!