Virulence Gene Regulation inBacillus anthracisand OtherBacillus cereusGroup Species

Abstract

The best-studied members of the Bacillus cereus group, B. anthracis, B. thuringiensis, and B. cereus sensu stricto, are pathogens with common and unique features that facilitate their ability to cause disease. As the etiological agent of anthrax, B. anthracis is the most renowned member of the B. cereus group. Inhalation or ingestion of B. anthracis spores can result in a lethal hemorrhagic septicemia. Anthrax toxin represents an interesting variation on the classic A-B toxin model: one binding/translocating B component, protective antigen (PA), and two enzymatic A components, edema factor (EF) and lethal factor (LF). Opportunistic infections caused by B. thuringiensis and B. cereus sensu stricto are relatively uncommon, but they can have serious consequences whether local or systemic. The chromosomes of B. anthracis, B. thuringiensis, and B. cereus sensu stricto reveal striking sequence similarity and gene synteny, but virulence-associated plasmid content can allow facile discrimination of the three species. A large number of virulence factors have been established for the pathogenic B. cereus group species. Anthrax toxin is the best-studied and arguably the most important virulence factor produced by B. anthracis. The entomopathogenesis of B. thuringiensis is dependent upon the production of characteristic insecticidal parasporal crystals called cryotoxins (Cry) and cytolysins (Cyt). B. anthracis, B. thuringiensis, and B. cereus senso stricto secrete pore-forming toxins of the cholesterol-dependent cytolysin (CDC) family.