Mycobacterium avium complex

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Mycobacterium avium complex
Scientific classification
Species complex:
Mycobacterium avium complex
Binomial name
Mycobacterium intracellulare
Runyon 1965,[1] ATCC 13950
Mycobacterium avium
Chester 1901 emend. Thorel et al. 1990

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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.[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.


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 

They are characterized as Gram-positive, nonmotile, acid-fast, short to long rods.[citation needed]

Colony characteristics

  • Usually, colonies are smooth, rarely rough, and not pigmented colonies. Older colonies may become yellow.


Differential characteristics

  • M. intracellulare and M. avium form the M. avium complex (MAC).
  • Remarkable ITS heterogeneity is seen within different M. intracellulare isolates.


Type strains

  • M. intracellulare type strains include ATCC 13950, CCUG 28005, CIP 104243, DSM 43223, JCM 6384, and NCTC 13025.[6]
  • M. avium type strains include ATCC 25291, DSM 44156, and TMC 724.[7]

Human health

a-c) Summary of the strategy of MAH related to mucosal epithelial cell adhesion and invasion[8]

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).[3]

MAC infection can cause COPD and lymphadenitis, and can cause disseminated disease, especially in people with immunodeficiency.[4]: 245 


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]


  1. Runyon, E. 1965. Pathogenic mycobacteria. Advances in Tuberculosis Research, 14, 235-287.
  2. "Mycobacterium Avium Complex. MAI; MAC Information". Patient Info. 29 August 2014. Archived from the original on 9 April 2023. Retrieved 16 December 2022.
  3. 3.0 3.1 "Mycobacterium Avium Complex infections | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program". Archived from the original on 2022-03-13. Retrieved 2020-03-29.
  4. 4.0 4.1 Jones-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. ISBN 9780702039355.
  5. Haworth CS, Banks J, Capstick T, Fisher AJ, Gorsuch T, Laurenson IF, Leitch A, Loebinger MR, Milburn HJ, Nightingale M, Ormerod P, Shingadia D, Smith D, Whitehead N, Wilson R, Floto RA (November 2017). "British Thoracic Society guidelines for the management of non-tuberculous mycobacterial pulmonary disease (NTM-PD)". Thorax. 72 (Suppl 2): ii1–ii64. doi:10.1136/thoraxjnl-2017-210927. PMID 29054853.
  6. "Type strain of Mycobacterium intracellulare at BacDive - the Bacterial Diversity Metadatabase". Archived from the original on 2017-02-02. Retrieved 2022-12-16.
  7. "Type strain of Mycobacterium avium at BacDive - the Bacterial Diversity Metadatabase". Archived from the original on 2018-10-14. Retrieved 2022-12-16.
  8. Shin, Min-Kyoung; Shin, Sung Jae (16 March 2021). "Genetic Involvement of Mycobacterium avium Complex in the Regulation and Manipulation of Innate Immune Functions of Host Cells". International Journal of Molecular Sciences. 22 (6): 3011. doi:10.3390/ijms22063011. ISSN 1422-0067.
  9. Henry, Ronnie (March 2017). "Etymologia: Mycobacterium chimaera". Emerg Infect Dis. 23 (3): 499. doi:10.3201/eid2303.ET2303. PMC 5382748. Citing public domain text from the CDC.
  10. Tortoli, E; Rindi, L; Garcia, MJ; Chiaradonna, P; Dei, R; Garzelli, C; Kroppenstedt, RM; Lari, N; Mattei, R; Mariottini, A; Mazzarelli, G; Murcia, MI; Nanetti, A; Piccoli, P; Scarparo, C (July 2004). "Proposal to elevate the genetic variant MAC-A, included in the Mycobacterium avium complex, to species rank as Mycobacterium chimaera sp. nov". International Journal of Systematic and Evolutionary Microbiology. 54 (Pt 4): 1277–85. doi:10.1099/ijs.0.02777-0. PMID 15280303.

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