Bacillus anthracis

Prior to the extraordinary interest in Bacillus anthracis generated by the recent bioterrorism events in the United States, much of microbiologists' awareness of the bacterium resulted from its historical significance. B. anthracis can infect all mammals, some birds, and possibly even reptiles. Systemic anthrax, generally resulting from inhalation or ingestion of B. anthracis spores, has a high fatality rate. B. anthracis is a facultative anaerobe and grows in most rich undefined media with a doubling time of approximately 30 min. Experimental studies of anthrax toxin are summarized in this chapter. The majority of animal models for anthrax have been used to assess pathophysiological effects of purified toxin and to test efficacy of vaccines against anthrax. When B. anthracis is grown under appropriate conditions, the outermost surface of vegetative cells is covered by a capsule. As is true for numerous pathogens, the capsule is an important virulence factor. Toxin and capsule synthesis by B. anthracis represents an intriguing example of coordinate expression of virulence genes in response to host-related cues. Major advances in understanding of structure and function of the “classic” virulence factors of B. anthracis, the anthrax toxin proteins and the poly-D-glutamic capsule, combined with new information regarding the anthrax toxin receptors are fueling new strategies for anthrax therapeutics and improved human vaccines. Molecular genetic analyses involving multiple B. anthracis strains will continue to facilitate epidemiological studies and development of advanced methods for detection and identification.