''Mycobacterium avium ''complex is a group of

mycobacteria ''Mycobacterium'' is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis ('' M. tuberculosis'') a ...

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 Dust is made of particle size, fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian processes, aeolian process), Types of volcan ...

and in soil. MAC bacteria usually cause infection in those who are

immunocompromised Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that affe ...

or those with severe

lung disease The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the backbone on either side of the heart. Their function in the respiratory syst ...

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 In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

, nonmotile,

acid-fast Acid-fastness is a physical property of certain bacterial and eukaryotic cells, as well as some sub-cellular structures, specifically their resistance to decolorization by acids during laboratory staining procedures. Once stained as part of a sa ...

, short to long rods. Colony characteristics * Usually, colonies are smooth, rarely rough, and not pigmented

colonies A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their '' metropole'' (or "mother country"). This separated rule was often or ...

. 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 Isoniazid, also known as isonicotinic acid hydrazide (INH), is an antibiotic used for the treatment of tuberculosis. For active tuberculosis, it is often used together with rifampicin, pyrazinamide, and either streptomycin or ethambutol. F ...

ethambutol Ethambutol (EMB, E) is a medication primarily used to treat tuberculosis. It is usually given in combination with other tuberculosis medications, such as isoniazid, rifampicin and pyrazinamide. It may also be used to treat ''Mycobacterium avi ...

rifampin Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), ''Mycobacterium avium'' complex, leprosy, and Legionnaires' disease. It is almost always used tog ...

, and

streptomycin Streptomycin is an antibiotic medication used to treat a number of bacterial infections, including tuberculosis, Mycobacterium avium complex, ''Mycobacterium avium'' complex, endocarditis, brucellosis, Burkholderia infection, ''Burkholderia'' i ...

. 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 ''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 nontu ...

'' ** '' 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

or who have severe

such as those with

cystic fibrosis Cystic fibrosis (CF) is a genetic disorder inherited in an autosomal recessive manner that impairs the normal clearance of Sputum, mucus from the lungs, which facilitates the colonization and infection of the lungs by bacteria, notably ''Staphy ...

or chronic obstructive lung disease (COPD). MAC infection can cause COPD and

lymphadenitis Lymphadenopathy or adenopathy is a disease of the lymph nodes, in which they are abnormal in size or consistency. Lymphadenopathy of an inflammatory type (the most common type) is lymphadenitis, producing swollen or enlarged lymph nodes. In cl ...

, and can cause disseminated disease, especially in people with

immunodeficiency Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that aff ...

. 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

External links

* {{DEFAULTSORT:Mycobacterium Intracellulare Acid-fast bacilli avium complex Bacteria described in 1965 Pathogenic bacteria