Atypical mycobacteria are species of mycobacteria that are similar to the mycobacteria that are the cause of tuberculosis. Like other mycobacteria, they are rod-like in shape and they are stained for observation by light microscopy using a specialized staining method called acid-fast staining. The need for this staining method reflects the unusual cell wall chemistry of mycobacteria, relative to other bacteria. In contrast to other mycobacteria, atypical mycobacteria do not cause tuberculosis. Accordingly, the group of bacteria is also described as nonpneumoniae mycobacteria. This group of bacteria is also designated as MOTT (mycobacteria other than tuberculosis). Examples of atypical mycobacteria include Mycobacterium kansasii, Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium marinum, and Mycobacterium ulcerans.

The atypical mycobacteria are widely present in the environment. They inhabit fresh and salt water, milk, soil, and the feces of birds. Other environmental niches, which so far have not been determined...