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 infectionsorMycobacterium avium complex infections in humans.[2] These bacteria are common and are found in fresh and salt water, in household dust and in soil.[3] MAC bacteria usually cause infection in those who are immunocompromised or those with severe lung disease.
Slant tubes of Löwenstein-Jensen medium. From left to right: - Negative control - M. tuberculosis: Dry-appearing colonies - Mycobacterium avium complex: Wet-appearing colonies - M. gordonae: Yellowish colonies
In the Runyon classification, both bacteria are nonchromogens. They can be differentiated from M. tuberculosis and each other by commercially available DNA probes.[4]: 245
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 fibrosisorchronic obstructive lung disease (COPD).[3]MAC infection can cause COPD and lymphadenitis, and can cause disseminated disease, especially in people with immunodeficiency.[4]: 245
During the last decade Mycobacterium chimaera (see below) infections following cardiothoracic surgery, especially open-heart surgery, have been increasingly reported worldwide.[8] Infections usually involve the respiratory system. Mycobacterium chimaera is acquired during cardiopulmonary bypass via bioaerosols emitted from contaminated heater-cooler units water systems. Due to nonspecific symptoms and long latency, postoperative Mycobacterium chimaera infections may not be promptly diagnosed and treated, and may become life-threatening.
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.[9][10]
^ abJones-Lopez, Edward C.; Ellner, Jerrold J. (2011). "Chapter 35: Tuberculosis and Atypical Mycobacterial Infections". In Guerrant, Richard L.; Walker, David H.; Weller, Peter F. (eds.). Tropical infectious diseases : principles, pathogens, & practice (3rd ed.). Edinburgh: Saunders. ISBN9780702039355.
