Mycobacterium avium complex

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

• 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. During the last decade Mycobacterium chimaera (see below) infections following cardiothoracic surgery, especially open-heart surgery, have been increasingly reported worldwide. 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.

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.

References

References

1. '''Runyon, E.''' 1965. Pathogenic mycobacteria. Advances in Tuberculosis Research, 14, 235-287.
2. (29 August 2014). "Mycobacterium Avium Complex. MAI; MAC Information". Patient Info.
3. "Mycobacterium Avium Complex infections {{!}} Genetic and Rare Diseases Information Center (GARD) – an NCATS Program".
4. (2011). "Tropical infectious diseases : principles, pathogens, & practice". Saunders.
5. (November 2017). "British Thoracic Society guidelines for the management of non-tuberculous mycobacterial pulmonary disease (NTM-PD)". Thorax.
6. [http://bacdive.dsmz.de/index.php?search=8403&submit=Search Type strain of ''Mycobacterium intracellulare'' at Bac''Dive'' - the Bacterial Diversity Metadatabase]
7. [http://bacdive.dsmz.de/index.php?site=search&rd=8419 Type strain of ''Mycobacterium avium'' at Bac''Dive'' - the Bacterial Diversity Metadatabase]
8. (2020). "Mycobacterium chimaera infections: An update". Journal of Infection and Chemotherapy.
9. Henry, Ronnie. (March 2017). "Etymologia: Mycobacterium chimaera". Emerg Infect Dis.
10. (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.