|
''Bordetella'' is a genus of small (0.2 - 0.7 µm), Gram-negative coccobacilli of the phylum Proteobacteria. ''Bordetella'' species, with the exception of ''B. petrii'', are obligate aerobes, as well as highly fastidious, or difficult to culture. Three species are human pathogens (''B. pertussis'', ''B. parapertussis'', ''B. bronchiseptica''); one of these (''B. bronchiseptica'') is also motile. ''B. pertussis'' and occasionally ''B. parapertussis'' cause pertussis or whooping cough in humans, and some ''B. parapertussis'' strains can colonise sheep. ''B. bronchiseptica'' rarely infects healthy humans, though disease in immunocompromised patients has been reported. ''B. bronchiseptica'' causes several diseases in other mammals, including kennel cough and atrophic rhinitis in dogs and pigs, respectively. Other members of the genus cause similar diseases in other mammals, and in birds (''B. hinzii'', ''B. avium''). The ''Bordetella'' genus is named after Jules Bordet. ==Pathogenesis== The most thoroughly studied of the ''Bordetella'' species are ''B. bronchiseptica'', ''B. pertussis'' and ''B. parapertussis'', and the pathogenesis of respiratory disease caused by these bacteria has been reviewed. Transmission occurs by direct contact, or via respiratory aerosol droplets, or fomites. Bacteria initially adhere to ciliated epithelial cells in the nasopharynx, and this interaction with epithelial cells is mediated by a series of protein adhesins. These include filamentous haemaglutinin, pertactin, fimbriae, and pertussis toxin (though expression of pertussis toxin is unique to ''B. pertussis''). As well as assisting in adherence to epithelial cells, some of these are also involved in attachment to immune effector cells. The initial catarrhal phase of infection produces symptoms similar to those of the common cold, and during this period, large numbers of bacteria can be recovered from the pharynx. Thereafter, the bacteria proliferate and spread further into the respiratory tract, where the secretion of toxins causes ciliostasis and facilitates the entry of bacteria to tracheal/bronchial ciliated cells. One of the first toxins to be expressed is tracheal cytotoxin, which is a disaccharide-tetrapeptide derived from peptidoglycan. Unlike most other ''Bordetella'' toxins, tracheal cytotoxin is expressed constitutively, being a normal product of the breakdown of the bacterial cell wall. Other bacteria recycle this molecule back into the cytoplasm, but in ''Bordetella'' and ''Neisseria gonorrhoeae'', it is released into the environment. Tracheal cytotoxin itself is able to reproduce paralysis of the ciliary escalator, inhibition of DNA synthesis in epithelial cells and ultimately killing of the same. One of the most important of the regulated toxins is adenylate cyclase toxin, which aids in the evasion of innate immunity. The toxin is delivered to phagocytic immune cells upon contact. Immune cell functions are then inhibited in part by the resulting accumulation of cyclic AMP. Recently discovered activities of adenylate cyclase toxin, including transmembrane pore formation and stimulation of calcium influx, may also contribute to the intoxication of phagocytes. 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「Bordetella」の詳細全文を読む スポンサード リンク
|