Abstract
The Bacillus cereus sensu lato group contains diverse Gram-positive spore-forming bacteria that can cause gastrointestinal diseases and severe eye infections in humans. They have also been incriminated in a multitude of other severe, and frequently fatal, clinical infections, such as osteomyelitis, septicaemia, pneumonia, liver abscess and meningitis, particularly in immuno-compromised patients and preterm neonates. The pathogenic properties of this organism are mediated by the synergistic effects of a number of virulence products that promote intestinal cell destruction and/or resistance to the host immune system. This review focuses on the pore-forming haemolysins produced by B. cereus: haemolysin I (cereolysin O), haemolysin II, haemolysin III and haemolysin IV (CytK). Haemolysin I belongs to the cholesterol-dependent cytolysin (CDC) family whose best known members are listeriolysin O and perfringolysin O, produced by L. monocytogenes and C. perfringens respectively. HlyII and CytK are oligomeric ß-barrel pore-forming toxins related to the α-toxin of S. aureus or the ß-toxin of C. perfringens. The structure of haemolysin III, the least characterized haemolytic toxin from the B. cereus, group has not yet been determined.
Highlights
The Bacillus cereus sensu lato group contains diverse Gram-positive spore-forming bacteria that are widespread in the environment
Given that B. anthracis spores can enter the host through the gastrointestinal (GI) route, and that the epithelial cell barrier is one of the major obstructions to infection in the GI tract, they proposed that anthrolysin O (ALO)-induced increase of intracellular calcium to alter tight junction architecture could lead to movement of the vegetative anthrax bacteria, or other bacterial toxins, into the surrounding tissues
We suggest that, when glucose is consumed by the bacteria and iron is sequestered by phagocytic cells as a natural host defence [82,83], the HlyIIR and ferric uptake regulator (Fur) repressors become inactivated and hlyII expression is triggered
Summary
The Bacillus cereus sensu lato group contains diverse Gram-positive spore-forming bacteria that are widespread in the environment. B. cereus produces several compounds (degradation enzymes, cytotoxic factors and cell-surface proteins) that might contribute to virulence [20,21,22,23,24,25,26], and the illnesses associated with this organism are probably mediated by the synergistic effects of a number of virulence products These products, known to accumulate only during stationary phase when high bacterial densities are reached, include two enterotoxic complexes (haemolysin BL (HBL) and non-haemolytic enterotoxin (NHE)), several phospholipases-C, a collagenase and various haemolysins/cytolysins (HlyI, HlyII, HlyIII and HlyIV) [13]. Were identified among the 198 strains [31]
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