Historically, most aerobic endospore‐forming bacteria were classified as species of
Bacillus
.
Bacillus
is the type genus of the
Bacillaceae
and contains the largest number of species. Aerobic endospore‐forming bacteria are ubiquitous in nature. Cases of anthrax due to laboratory accidents, biological warfare, and bioterrorism events are also rare, but ongoing vigilance in the clinical microbiology laboratory is critical. This chapter describes the clinically significant infections involving
Bacillus
,
Brevibacillus
,
Lysinibacillus
, and
Paenibacillus
species. Members of the
B. cereus
group, other than
B. anthracis
,have been isolated from diverse ecological niches and are widely distributed in nature. Gastrointestinal anthrax is suspected only if an adequate history of the patient is known. Anthrax meningitis may occur on its own or, more frequently, as a complication of another form of the disease.