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).
For example, Mycobacterium tuberculosis is an infamous species. This is the organism that causes human tuberculosis. Mycobacterium leprae is the organism that causes leprosy.
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). Every year in the United States approximately two people per 100,000 population develop infections caused by these lesser-known "cousins" of TB and leprosy. In fact, for unknown reasons, data suggest that there may be rising numbers of cases in certain parts of the country.
The most common NTM's that require treatment are M. avium, M. intracellulare , M. kansasii, M. abscessus, M. chelonae, M. fortuitum, M. terrae, M. xenopi and M. simiae. Among the NTM, there are three species which predominantly involve the skin: M. leprae, M. ulcerans, and M. marinum.