Bacillus anthracis: Difference between revisions

It is one of few bacteria known to synthesize a weakly immunogenic and antiphagocytic [[Bacterial capsule|protein capsule]] (poly-D-gamma-glutamic acid) that disguises the vegetative bacterium from the host immune system.<ref>Choo, M. K., Sano, Y., Kim, C., Yasuda, K., Li, X. D., Lin, X., … Park, J. M. (2017). TLR sensing of bacterial spore-associated RNA triggers host immune responses with detrimental effects. ''Journal of Experimental Medicine'', ''214''(5), 1297–1311. {{doi|10.1084/jem.20161141}}</ref> Most bacteria are surrounded by a polysaccharide capsule rather than poly-g-D-glutamic acid which provides an evolutionary advantage to ''B. anthracis''. Polysaccharides are associated with adhesion of neutrophil-secreted [[defensin]]s that inactivate and degrade the bacteria. By not containing this macromolecule in the capsule, ''B. anthracis'' can evade a [[neutrophil]]ic attack and continue to propagate infection. The difference in capsule composition is also significant because poly-g-D-glutamic acid has been hypothesized to create a negative charge which protects the vegetative phase of the bacteria from phagocytosis by [[macrophage]]s.<ref>Choudhury, B., Leoff, C., Saile, E., Wilkins, P., Quinn, C. P., Kannenberg, E. L., & Carlson, R. W. (2006). The Structure of the Major Cell Wall Polysaccharide of Bacillus anthracis is Species-specific. ''Journal of Biological Chemistry'', ''281''(38), 27932–27941. {{doi|10.1074/jbc.M605768200}}</ref> The capsule is degraded to a lower molecular mass and released from the bacterial cell surface to act as a decoy to protect the bacteria from [[Complement system#:~:text=The complement system, also known, attack the pathogen's cell membrane.|complement]].<ref>Makino, S., M. Watarai, H. I. Cheun, T. Shirahata, and I. Uchida. 2002. Effect of the lower molecular capsule released from the cell surface of Bacillus anthracis on the pathogenesis of anthrax. J. Infect. Dis. 186:227–233.</ref>

 

 

The endospore 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 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 [[wikt:refractile|refractile]] and contain [[dipicolinic acid]]. Electron micrograph sections show they have a thin outer endospore coat, a thick [[spore cortex]], and an inner [[spore membrane]] surrounding the endospore contents. The endospores resist heat, drying, and many disinfectants (including 95% ethanol).<ref>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</ref> Because of these attributes, ''B. anthracis'' endospores are extraordinarily well-suited to use (in powdered and aerosol form) as [[biological weapon]]s. Such weaponization has been accomplished in the past by at least five state bioweapons programs—those of the [[United Kingdom]], [[Imperial Japan|Japan]], the [[United States]], [[Russia]], and [[Iraq]]—and has been attempted by several others.<ref>Zilinskas, Raymond A. (1999), "Iraq's Biological Warfare Program: The Past as Future?", Chapter 8 in: [[Joshua Lederberg|Lederberg, Joshua]] (editor), ''Biological Weapons: Limiting the Threat'' (1999), [[The MIT Press]], pp 137-158.</ref>