mycobacterium avium complex 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 mycobacterium avium-intracellulare infections or mycobacterium avium complex infections in humans. 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. not to be confused with mycobacterium tuberculosis complex. mycobacterium avium complex scientific classification domain: bacteria phylum: actinomycetota class: actinomycetia order: mycobacteriales family: mycobacteriaceae genus: mycobacterium species complex: mycobacterium avium complex binomial name mycobacterium intracellularerunyon 1965, atcc 13950 mycobacterium aviumchester 1901 emend. thorel et al. 1990 description in the runyon classification, both bacteria are nonchromogens. they can be differentiated from m. tuberculosis and each other by commercially available dna probes.: 245 they are characterized as gram-positive, nonmotile, acid-fast, short to long rods. colony characteristics usually, colonies are smooth, rarely rough, and not pigmented colonies. older colonies may become yellow. physiology growth on löwenstein-jensen medium and middlebrook 7h10 agar occurs at 37°c after seven or more days. the complex can be (but is not often) resistant to isoniazid, ethambutol, rifampin, and streptomycin. differential characteristics m. intracellulare and m. avium form the m. avium complex (mac). remarkable its heterogeneity is seen within different m. intracellulare isolates. species mycobacterium avium mycobacterium avium subsp. paratuberculosis 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.: 245 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.