Mycobacterium avium complex
Mycobacterium avium "complex is a group of mycobacteria comprising Mycobacterium intracellulare and Mycobacterium avium" that are commonly grouped because they infect humans together; this group, in turn, is part of the group of nontuberculous mycobacteria. These bacteria cause disease in humans called "Mycobacterium avium-intracellulare" infection or "Mycobacterium avium" complex infection. These bacteria are common and are found in fresh and salt water, in household dust and in soil. MAC bacteria usually cause infection in those who are immunocompromised or those with severe lung disease. Description. In the Runyon classification, both bacteria are nonchromogens. They can be  differentiated from "M. tuberculosis" and each other by commercially available DNA probes. They are characterized as Gram-positive, nonmotile, acid-fast, short to long rods. Colony characteristics Physiology Differential characteristics Type strains. "M. intracellulare" type strains include ATCC 13950, CCUG 28005, CIP 104243, DSM 43223, JCM 6384, and NCTC 13025. "M. avium" type strains include ATCC 25291, DSM 44156, and TMC 724. Human health. MAC bacteria enter most people's body when inhaled into the lungs or swallowed, but only cause infection in those who are immunocompromised or who have severe lung disease such as those with cystic fibrosis or  chronic obstructive lung disease (COPD). MAC infection can cause COPD and lymphadenitis, and can cause disseminated disease, especially in people with immunodeficiency. History. In 2004, Tortoli et al. proposed the name "M. chimaera" for strains that a reverse hybridization–based line probe assay suggested belonged to MAIS ("M. avium–M. intracellulare–M. scrofulaceum" group), but were different from "M. avium", "M. intracellulare", or "M. scrofulaceum". The new species name comes from the Chimera, a mythological being made up of parts of three different animals.