Mycobacterium
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 TEM micrograph of M. tuberculosis.
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Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. It includes many pathogens known to cause serious diseases in mammals, including tuberculosis and leprosy.
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[edit] Common microbiologic characteristics of the genus
Most mycobacteria are classified into two categories: fast-growing and slow-growing, based on laboratory growth characteristics. All mycobacteria are aerobic and acid fast.
All Mycobacteria share a characteristic cell wall, thicker than in many other bacteria, which is hydrophobic, waxy, and rich in mycolic acids/mycolates. The mycobacterial cell wall makes a substantial contribution to the hardiness of this genus.
Mycobacteria tend to be difficult to culture (fastidious), sometimes taking over two years to develop in culture. As well as being fastidious, some species also have extremely long reproductive cycles (M. leprae, for example, may take more than 20 days to proceed through one division cycle; E. coli, for comparison, takes only 20 minutes), making laboratory culture a slow process.
[edit] Staining characteristics
Mycobacteria are classical acid-fast organisms. Stains used in evaluation of tissue specimens or microbiological specimens include Fite's stain, Ziehl-Neelsen stain, and Kinyoun stain.
[edit] Mycobacterium ecological characterisitics
Mycobacteria are widespread organisms, typically living in water (including tap water treated with chlorine) and food sources. Some, however, including the tuberculosis and the leprosy organisms, appear to be obligate parasites and are not found as free-living members of the genus.
[edit] Mycobacteria as pathogens
Mycobacteria can colonize their hosts without the hosts showing any adverse signs. For example, billions of people around the world are infected with M. tuberculosis but will never know it because they will not develop symptoms.
Mycobacterial infections are notoriously difficult to treat. The organisms are hardy due to their cell wall, which is neither truly Gram negative nor positive, and unique to the family, they are naturally resistant to a number of antibiotics that work by destroying cell walls, such as penicillin. Also, because of this cell wall, they can survive long exposure to acids, alkalis, detergents, oxidative bursts, lysis by complement and antibiotics which naturally leads to antibiotic resistance. Most mycobacteria are susceptible to the antibiotics clarithromycin and rifamycin, but antibiotic-resistant strains are known to exist.
[edit] Medical classification
Mycobacteria can be classified into several major groups for purpose of diagnosis and treatment: M. tuberculosis complex which can cause tuberculosis: M. tuberculosis, M. bovis, M. africanum, and M. microti; M. leprae which causes Hansen's disease or leprosy; Nontuberculous mycobacteria (NTM) are all the other mycobacteria which can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, or disseminated disease.
[edit] Established Species of Mycobacteria
- M. abscessus
- M. africanum
- M. agri
- M. aichiense
- M. alvei
- M. arupense
- M. asiaticum
- M. aubagnense
- M. aurum
- M. austroafricanum
- Mycobacterium avium complex (MAC), is a group of species which are a significant cause of death in AIDS patients. Species in this complex include:
- M. avium
- M. avium paratuberculosis, which has been implicated in Crohn's disease in humans and Johne's disease in sheep
- M. avium silvaticum
- M. avium "hominissuis"
- M. boenickei
- M. bohemicum
- M. bolletii
- M. botniense
- M. bovis
- M. branderi
- M. brisbanense
- M. brumae
- M. canariasense
- M. caprae
- M. celatum
- M. chelonae,
- M. chimaera
- M. chitae
- M. chlorophenolicum
- M. chubuense
- M. colombiense
- M. conceptionense
- M. confluentis
- M. conspicuum
- M. cookii
- M. cosmeticum
- M. diernhoferi
- M. doricum
- M. duvalii
- M. elephantis
- M. fallax
- M. farcinogenes
- M. flavescens
- M. florentinum
- M. fluoroanthenivorans
- M. fortuitum
- M. fortuitum subsp. acetamidolyticum
- M. frederiksbergense
- M. gadium
- M. gastri
- M. genavense
- M. gilvum
- M. goodii
- M. gordonae
- M. haemophilum
- M. hassiacum
- M. heckeshornense
- M. heidelbergense
- M. hiberniae
- M. hodleri
- M. holsaticum
- M. houstonense
- M. immunogen
- M. interjectum
- M. intermedium
- M. intracellulare
- M. kansasii
- M. komossense
- M. kubicae
- M. kumamotonense
- M. lacus
- M. lentiflavum
- M. leprae, which causes leprosy
- M. lepraemurium
- M. madagascariense
- M. mageritense
- M. malmoense
- M. marinum
- M. massiliense
- M. microti
- M. monacense
- M. montefiorense
- M. moriokaense
- M. mucogenicum
- M. murale
- M. nebraskense
- M. neoaurum
- M. neworleansense
- M. nonchromogenicum
- M. novocastrense
- M. obuense
- M. palustre
- M. parafortuitum
- M. parascrofulaceum
- M. parmense
- M. peregrinum
- M. phlei
- M. phocaicum
- M. pinnipedii
- M. porcinum
- M. poriferae
- M. pseudoshottsii
- M. pulveris
- M. psychrotolerans
- M. pyrenivorans
- M. rhodesiae
- M. saskatchewanense
- M. scrofulaceum
- M. senegalense
- M. seoulense
- M. septicum
- M. shimoidei
- M. shottsii
- M. simiae
- M. smegmatis
- M. sphagni
- M. szulgai
- M. terrae
- M. thermoresistibile
- M. tokaiense
- M. triplex
- M. triviale
- Mycobacterium tuberculosis complex (MTBC),members are causative agents of human and animal tuberculosis. Species in this complex include:
- M. tuberculosis, the major cause of human tuberculosis
- M. bovis
- M. bovis BCG
- M. africanum
- M. canetti
- M. caprae
- M. pinnipedii'
- M. tusciae
- M. ulcerans, which causes the "Buruli", or "Bairnsdale, ulcer"
- M. vaccae
- M. vanbaalenii
- M. wolinskyi
- M. xenopi
[edit] References
- Diagnosis and Treatment of Disease Caused by Nontuberculous Mycobacteria. American Thoracic Society. Am J Respiratory and Critical Care Medicine. Aug 1997 156(2) Part 2 Supplement PDF format
- RIDOM - Ribosomal Differentiation of Medical Microorganisms [1]
- J.P. Euzéby: List of Prokaryotic Names with Standing in Nomenclature - Genus Mycobacterium [2]
[edit] See also
- Leprosy (Hansen's disease)
- Tuberculosis
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