Nontuberculous mycobacteria (NTM), also known as environmental mycobacteria, atypical mycobacteria and mycobacteria other than tuberculosis (MOTT), are mycobacteria which do not cause tuberculosis or leprosy (also known as Hansen's disease). NTM do cause pulmonary diseases that resemble tuberculosis. Mycobacteriosis is any of these illnesses, usually meant to exclude tuberculosis. They occur in many animals, including humans and are commonly found in soil and water. Introduction Mycobacteria are a family of small, rod-shaped bacilli that can be classified into three main groups for the purpose of diagnosis and treatment: Mycobacterium tuberculosis complex, which can cause tuberculosis: M. tuberculosis, M. bovis, M. africanum, M. microti and M. canetti M. leprae and M. lepromatosis, which cause Hansen's disease, also called leprosy Nontuberculous mycobacteria (NTM) are all the other mycobacteria that can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, or disseminated disease. Although over 150 different species of NTM have been described, pulmonary infections are most commonly due to Mycobacterium avium complex (MAC), Mycobacterium kansasii, and Mycobacterium abscessus (see image). Taxonomy In 1959, botanist Ernest Runyon put these human disease-associated bacteria into four groups (Runyon classification): Photochromogens develop pigments in or after being exposed to light. Examples include M. kansasii, M. simiae, and M. marinum. Scotochromogens become pigmented in darkness. Examples include M. scrofulaceum and M. szulgai. Nonchromogens include a group of prevalent opportunistic pathogens called M. avium complex (MAC). Other examples are M. ulcerans, M. xenopi, M. malmoense, M. terrae, M. haemophilum, and M. genavense. Rapid growers include four well-recognized, pathogenic, rapidly growing, nonchromogenic species: M. chelonae, M. abscessus, M. fortuitum, and M. peregrinum. Other examples cause disease rarely, such as M. smegmatis and M. flavescens. The number of identified and cataloged NTM species has been increasing rapidly, from about 50 in 1997 to over 125 by January 2007. The surge is mainly due to improved isolation and identification techniques. Even with these new techniques, though, the Runyon classification is still sometimes used to organize the mycobacteria into categories. Epidemiology NTM are widely distributed in the environment, particularly in wet soil, marshland, streams, rivers and estuaries. Different species of NTM prefer different types of environment. Human disease is believed to be acquired from environmental exposures. Unlike tuberculosis and leprosy, animal-to-human or human-to-human transmission of NTM rarely occurs. NTM diseases have been seen in most industrialized countries, where incidence rates vary from 1.0 to 1.8 cases per 100,000 persons. Recent studies, including one