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Bacillus anthracis
''Bacillus anthracis'' is the etiologic agent of anthrax—a common disease of livestock and, occasionally, of humans—and the only obligate pathogen within the genus ''Bacillus''. ''B. anthracis'' is a Gram-positive, endospore-forming, rod-shaped bacterium, with a width of 1.0–1.2 µm and a length of 3–5 µm.〔 It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions.〔Holt, J. G., N. R. Krieg, P. H. A. Sneath, J. T. Staley, and S. T. Williams. 1994. Group 17: gram-positive cocci, p. 527–558. In W. R. Hensyl (ed.), Bergey's manual of determinative bacteriology, 9th ed. Williams and Wilkins, Baltimore, Md.〕
It is one of few bacteria known to synthesize a protein capsule (poly-D-gamma-glutamic acid). Like ''Bordetella pertussis'', it forms a calmodulin-dependent adenylate cyclase exotoxin known as (edema factor), along with lethal factor. It bears close genotypical and phenotypical resemblance to ''Bacillus cereus'' and ''Bacillus thuringiensis''. All three species share cellular dimensions and morphology. All form oval spores located centrally in an unswollen sporangium. ''B. anthracis'' spores, in particular, are highly resilient, surviving extremes of temperature, low-nutrient environments, and harsh chemical treatment over decades or centuries.
The spore is a dehydrated cell with thick walls and additional layers that form inside the cell membrane. It can remain inactive for many years, but if it comes into a favorable environment, it begins to grow again. It is sometimes called an endospore because it initially develops inside the rod-shaped form. Features such as the location within the rod, the size and shape of the endospore, and whether or not it causes the wall of the rod to bulge out are characteristic of particular species of ''Bacillus''. Depending upon the species, the endospores are round, oval, or occasionally cylindrical. They are highly refractile and contain dipicolinic acid. Electron micrograph sections show they have a thin outer spore coat, a thick spore cortex, and an inner spore membrane surrounding the spore contents. The spores resist heat, drying, and many disinfectants (including 95% ethanol).〔Bergey's Manual of Systematic Bacteriology, vol. 2, p. 1105, 1986, Sneath, P.H.A.; Mair, N.S.; Sharpe, M.E.; Holt, J.G. (eds.); Williams & Wilkins, Baltimore, Maryland, USA〕 Because of these attributes, ''B. anthracis'' spores are extraordinarily well-suited to use (in powdered and aerosol form) as biological weapons. Such weaponization has been accomplished in the past by at least five state bioweapons programs—those of the United Kingdom, Japan, the United States, Russia, and Iraq—and has been attempted by several others.〔Zilinskas, Raymond A. (1999), "Iraq's Biological Warfare Program: The Past as Future?", Chapter 8 in: Lederberg, Joshua (editor), ''Biological Weapons: Limiting the Threat'' (1999), The MIT Press, pp 137-158.〕
== Historical background ==
French physician Casimir Davaine (1812-1882) demonstrated the symptoms of anthrax were invariably accompanied by the microbe ''B. anthracis''. German physician Aloys Pollender (1799–1879) is also credited for this discovery. ''B. anthracis'' was the first bacterium conclusively demonstrated to cause disease, by Robert Koch in 1876.〔Koch, R. (1876) "Untersuchungen über Bakterien: V. Die Ätiologie der Milzbrand-Krankheit, begründet auf die Entwicklungsgeschichte des ''Bacillus anthracis''" (Investigations into bacteria: V. The etiology of anthrax, based on the ontogenesis of ''Bacillus anthracis''), Cohns ''Beitrage zur Biologie der Pflanzen'', vol. 2, no. 2, (pages 277–310 ).〕 The species name ''anthracis'' is from the Greek ''anthrax'' (ἄνθραξ), meaning "coal" and referring to the most common form of the disease, cutaneous anthrax, in which large, black skin lesions are formed.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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