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''Mycobacterium tuberculosis'' is an (obligate ) pathogenic bacterial species in the family Mycobacteriaceae and the causative agent of most cases of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' has an unusual, waxy coating on its cell surface (primarily due to the presence of mycolic acid), which makes the cells impervious to Gram staining; ''M. tuberculosis'' can appear Gram negative and Gram positive in clinical settings. The Ziehl-Neelsen stain, or acid-fast stain, is used instead. The physiology of ''M. tuberculosis'' is highly aerobic and requires high levels of oxygen. Primarily a pathogen of the mammalian respiratory system, it infects the lungs. The most frequently used diagnostic methods for tuberculosis are the tuberculin skin test, acid-fast stain, and chest radiographs.〔 The ''M. tuberculosis'' genome was sequenced in 1998. ==Pathophysiology== ''M. tuberculosis'' requires oxygen to grow and can be cultured in the laboratory. It does not retain any bacteriological stain due to high lipid content in its wall, hence Ziehl-Neelsen staining, or acid-fast staining, is used. Mycobacteria have an outer membrane. ''M. tuberculosis'' divides every 15–20 hours, which is extremely slow compared to other bacteria, which tend to have division times measured in minutes (''Escherichia coli'' can divide roughly every 20 minutes). It is a small bacillus that can withstand weak disinfectants and can survive in a dry state for weeks. Its unusual cell wall, rich in lipids (e.g., mycolic acid), is likely responsible for this resistance and is a key virulence factor. Humans are the only known reservoirs of ''M. tuberculosis''. When in the lungs, ''M. tuberculosis'' is taken up by alveolar macrophages, but they are unable to digest and eradicate the bacterium. Its cell wall prevents the fusion of the phagosome with the lysosome, which contains a host of antimycobacterial factors. Specifically, ''M. tuberculosis'' blocks the bridging molecule, early endosomal autoantigen 1 (EEA1); however, this blockade does not prevent fusion of vesicles filled with nutrients. Consequently, the bacteria multiply unchecked within the macrophage. The bacteria also carry the ''UreC'' gene, which prevents acidification of the phagosome. In addition, production of the diterpene isotuberculosinol prevents maturation of the phagosome. The bacteria also evade macrophage-killing by neutralizing reactive nitrogen intermediates. The ability to construct ''M. tuberculosis'' mutants and test individual gene products for specific functions has significantly advanced the understanding of the pathogenesis and virulence factors of ''M. tuberculosis''. Many secreted and exported proteins are known to be important in pathogenesis. Aerolysin is a virulence factor of the pathogenic bacterium Aeromonas hydrophila. Resistant strains of mycobacterium tuberculosis have developed resistance to more than one TB drug, due to mutations in their genes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mycobacterium tuberculosis」の詳細全文を読む スポンサード リンク
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