Abstract
Bacillus cereus is a ubiquitous soil bacterium responsible for two types of food-associated gastrointestinal diseases. While the emetic type, a food intoxication, manifests in nausea and vomiting, food infections with enteropathogenic strains cause diarrhea and abdominal pain. Causative toxins are the cyclic dodecadepsipeptide cereulide, and the proteinaceous enterotoxins hemolysin BL (Hbl), nonhemolytic enterotoxin (Nhe) and cytotoxin K (CytK), respectively. This review covers the current knowledge on distribution and genetic organization of the toxin genes, as well as mechanisms of enterotoxin gene regulation and toxin secretion. In this context, the exceptionally high variability of toxin production between single strains is highlighted. In addition, the mode of action of the pore-forming enterotoxins and their effect on target cells is described in detail. The main focus of this review are the two tripartite enterotoxin complexes Hbl and Nhe, but the latest findings on cereulide and CytK are also presented, as well as methods for toxin detection, and the contribution of further putative virulence factors to the diarrheal disease.
Highlights
Bacillus cereus is estimated to be responsible for 1.4%–12% of all food poisoning outbreaks worldwide [1]
Starchy foodstuffs such as rice or pasta are connected to food intoxications with emetic B. cereus, but more recently evidence is growing that emetic B. cereus are much more volatile than once thought
B. thuringiensis has been isolated from a variety of foodstuffs and the presence of the enterotoxin genes nhe, hbl and cytK-2 has been shown, with similar percentages as for B. cereus [57,60,72,90,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125], while ces genes have not been found [126,127]
Summary
Bacillus cereus is estimated to be responsible for 1.4%–12% of all food poisoning outbreaks worldwide [1]. Virulence/enterotoxin gene patterns are compiled for B. cereus which has been mainly isolated from foods, and from clinical, soil and environmental samples worldwide Those patterns are highly diverse [41,42,43,44,45,46,47]. B. thuringiensis has been isolated from a variety of foodstuffs and the presence of the enterotoxin genes nhe, hbl and cytK-2 has been shown, with similar percentages as for B. cereus [57,60,72,90,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125], while ces genes have not been found [126,127]. It has been reported that specific antibiotics, which provoke the production of small colony variants (SCVs), could lead to dysregulation of cereulide synthesis resulting in derailed cereulide levels [174]
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