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. 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.