Mycobacterium
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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, the fast-growing kind and the slow-growing kind, 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 fastidious (difficult to culture), 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 and 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 utilize the destruction of 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] Species of medically important Mycobacteria
- M. abscessus, which is also a common water contaminant and was until recently thought to be a subspecies of M. chelonae.
- M. africanum
- M. asiaticum
- Mycobacterium avium complex (MAC), which is a significant cause of death in AIDS patients. This complex also includes M. avium paratuberculosis, which has been implicated in Crohn's disease in humans and Johne's disease in sheep.
- M. bovis
- M. chelonae, which is a common water contaminant and can also infect wounds.
- M. fortuitum
- M. gordonae
- M. haemophilum
- M. intracellulare
- M. kansasii, which can cause life-threatening infections in people with compromised immune systems
- M. lentiflavum
- M. leprae, which causes leprosy
- M. liflandii, which causes a Buruli ulcer-like disease in frogs.
- M. malmoense
- M. marinum
- M. microti
- M. phlei
- M. pseudoshottsii
- M. scrofulaceum
- M. shottsii
- M. smegmatis
- M. triplex
- M. tuberculosis, which causes tuberculosis
- M. ulcerans, which causes the "Buruli", or "Bairnsdale, ulcer"
- M. uvium
- M. xenopi
[edit] Reference
- 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
[edit] See also
- Leprosy (Hansen's disease)
- Tuberculosisde:Mykobakterien
es:Mycobacterium fa:مایکوباکتریوم fr:Mycobacteriaceae ko:미코박테륨 it:Mycobacterium nl:Mycobacterium pl:Prątki pt:Mycobacterium
