Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis and [[leprosy. The Latin prefix "myco—" means both fungus and wax; its use here relates to the "waxy" compounds in the cell wall.
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Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis and [[leprosy. The Latin prefix "myco—" means both fungus and wax; its use here relates to the "waxy" compounds in the cell wall.
Microbiologic characteristics
Mycobacteria are aerobic and nonmotile bacteria (except for the species Mycobacterium marinum which has been shown to be motile within macrophages) that are characteristically acid-alcohol fast. Mycobacteria do not contain endospores or capsules, and are usually considered Gram-positive. While mycobacteria do not seem to fit the Gram-positive category from an empirical standpoint (i.e. they do not retain the crystal violet stain), they are classified as an acid-fast Gram-positive bacterium due to their lack of an outer cell membrane. All Mycobacterium species share a characteristic cell wall, thicker than in many other bacteria, which is hydrophobic, waxy, and rich in mycolic acids/mycolates. The cell wall makes a substantial contribution to the hardiness of this genus.
Many Mycobacterium species adapt readily to growth on very simple substrates, using ammonia or amino acids as nitrogen sources and glycerol as a carbon source in the presence of mineral salts. Optimum growth temperatures vary widely according to the species and range from 25 °C to over 50 °C.
Some species can be very difficult to culture (i.e. they are fastidious), sometimes taking over two years to develop in culture.Fact: date=August 2007 Further, some species also have extremely long reproductive cycles — M. leprae, may take more than 20 days to proceed through one division cycle (for comparison, some E. coli strains take only 20 minutes), making laboratory culture a slow process. In addition, the availability of genetic manipulation techniques still lags far behind that of other bacterial species.
A natural division occurs between slowly– and rapidly–growing species. Mycobacteria that form colonies clearly visible to the naked eye within 7 days on subculture are termed rapid growers, while those requiring longer periods are termed slow growers. Mycobacteria are slightly curved or straight rods between 0.2-0.6 µm wide by 1.0-10 µm long.
Pigmentation
Some mycobacteria produce carotenoid pigments without light. Others require photoactivation for pigment production.
