Bacillus

Bacillus species are rod-shaped, endospore-forming, aerobic or facultatively anaerobic, Gram-positive bacteria; in some species, cultures may become Gram-negative with age. The many species of the genus exhibit a wide range of physiological capabilities that enable them to live in any natural environment. Only one endospore is formed per cell. The spores are resistant to heat, cold, radiation, desiccation, and disinfectants. Bacillus anthracis requires oxygen for spore formation; this limitation has important consequences for epidemiology and control. In vivo, B. anthracis produces a polypeptide capsule (polyglutamic acid) that protects it from phagocytosis. The genera Bacillus and Clostridium form the family Bacillaceae.

Bacillus species are used in many medical, pharmaceutical, agricultural and industrial processes that take advantage of their wide range of physiological properties and their ability to produce a variety of enzymes, antibiotics and other metabolites. Bacitracin and polymyxin are two well-known antibiotics derived from Bacillus species. Several species are used as standards in medical and pharmaceutical tests.

On the other hand, the spores' resistance to sterilization and disinfection makes them problematic contaminants in food, medical supplies, surgical procedures, etc.

The virulence factors of B anthracis are its capsule and the three-component toxin, both of which are encoded on plasmids. Bacillus cereus produces numerous enzymes and aggressins. The major virulence factors are a necrotizing enterotoxin and a potent hemolysin (cereolysin). Nausea-causing food poisoning probably results from the release of emetic factors from certain foods by bacterial enzymes.

The reasons for marked differences in susceptibility to anthrax in different animal species are not known. The protective effect of the live spore vaccine for animals or the chemical human vaccines is based on the induction of humoral and cell-mediated immunity against the protective antigenic component of the anthrax toxin.

1. Klimpel KR et al. (1994) Anthrax toxin lethal factor contains a zinc metalloprotease consensus sequence which is required for lethal toxin activity. Molecular Microbiol13:1093.
2. Kramer JM et al (1989) Bacillus cereus and other Bacillus species. p.21. In Doyle MP (ed): Foodborne Bacterial Pathogens. Marcel Dekker, New York, 1989.
3. Turnbull PCB (1976) Studies on the production of enterotoxins by Bacillus cereus. J Clin Pathol29:941.