The Bacillus cereus group

The Bacillus cereus group, a group of highly phylogenetically related Bacillus species, includes the commonly studied species B. cereus, B. anthracis, and B. thuringiensis, as well as psychrotolerant (B. weihenstephanensis and B. wiedmannii), thermotolerant (B. cytotoxicus), morphologically distinct (B. mycoides and B. pseudomycoides) and probiotic (B. toyonensis) species. Nine novel Bacillus species have recently been isolated from marine sediments and seawater. The bacteria of this group, except B. anthracis, can cause systemic and local clinical cases, like pulmonary, eye, or wound infections. They are also notorious food pathogens causing diarrhea or vomiting. Emetic isolates usually represent a narrow lineage and synthesize thermostable plasmid-encoded toxin. The toxins nonhemolytic enterotoxin, hemolysin BL [a tripartite enterotoxin, consisting of a binding component (B) and two lytic components (L1 and L2)], and cytotoxin K have been rather well characterized. The global regulator PlcR has been intensively studied and unambiguously related to the regulation of toxins and multiple virulence factors. In recent years, the whole genome sequence of B. cereus strains has provided considerable information for genomic and functional studies. This chapter includes a survey of known virulence factors and outlines their potential or demonstrated contributions to virulence, in particular in relation to the group taxonomy.