Germs, like plants and animals, have been classified into similar groups. The groups are called "families." One such family of germs is known as the Mycobacteriaceae. Within this family there are a number of species. Some species can cause human diseases (pathogenic). Others species do not cause human diseases (saprophytic).
The Nontuberculous mycobacteria (NTM) refers to all the species in the family of mycobacteria that may cause human disease, but do not cause tuberculosis (TB). NTM most commonly affects the lungs, however there are three species which predominantly involve the skin: M. leprae (the cause of leprosy), M. ulcerans (the cause of Buruli Ulcer) and M. marinum (fish tank infection). Leprosy and Buruli Ulcer are exceedingly more rare in the United States. However, infections with M. marinum are seen in low, but consistent, numbers.