The Food Poisoning Toxins of Bacillus cereus

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.

Structure Revision of Isocereulide A, an Isoform of the Food Poisoning Emetic Bacillus cereus Toxin Cereulide

“…The CesNRPS genes, which are located on a virulence megaplasmid pXO1 [10,11], are organized as an operon. Apart from the structural cereulide synthetase genes cesA and cesB, the ces gene locus comprises a phosphopantheteintransferase involved in the activation of the NRPS machinery, a type II thioesterase with a proofreading function and an ABC transporter, recently shown not only to be involved in cereulide export but also directly in cereulide biosynthesis [12][13][14]. A peptidyl carrier protein (PCP)-coupled D-O-Leu-D-Ala didepsipeptide intermediate is generated by CesA with an in situ reduced D-Leu moiety coupled to D-Ala. Analogously, CesB assembles one in situ reduced L-Val unit with L-Val to form the corresponding L-O-Val-L-Val intermediate [15,16].…”

Detection and Isolation of Emetic Bacillus cereus Toxin Cereulide by Reversed Phase Chromatography

“…Due to the lack of fast and specific cereulide quantification and isolation methods, purification and quantification of the toxin is still laborious. Nevertheless, considerable progress has been made in the diagnostics of emetic B. cereus [30], and methods for specific detection of emetic B. cereus strains by matrix-assisted laser desorption/ionization-time-offlight (MALDI-ToF) mass spectrometry (MS) have been published recently [31,32]. Since MALDI-ToF MS is increasingly used in routine microbiology laboratories, it is expected that these methods, allowing the discrimination of emetic and non-emetic B. cereus, will significantly improve differential B. cereus diagnostics in clinical settings, as well as in foodborne outbreak situations.…”

Bacillus cereus Toxins

“…While emetic strains are mainly associated with starchy foodstuffs such as rice and pasta, enteropathogenic isolates are detected in all kinds of foods, including milk products, vegetables, meat products, sauces, soups, puddings, spices, poultry, and sprouts. The numerous studies performed on its prevalence and survival in different foods, as well as on the distribution of its toxin genes, are summarized in two reviews belonging to this Special Issue [ 9 , 10 ]. Additionally, Sánchez-Chica et al determined the presence and toxigenic and genomic diversity of B. cereus sensu lato isolates of a yet barely investigated raw material, cassava starch, from bakeries and powdered food companies in Colombia.…”

“…In a comprehensive review, 30 years of work on the food as well as cereulide and CytK. The latest finding on the genetic organization, the highly variable gene expression and toxin secretion, the mode of action, and the effects on target cells are shown [ 10 ]. Of special interest is the mode of pore formation of the tripartite enterotoxins Hbl and Nhe.…”

“…Besides the enterotoxins and their fascinating mode of action, this Special Issue also focuses on methods for toxin detection and for the prevention of illness, as well as on the contributions of further putative virulence factors to the disease. On the one hand, these topics are summarized in the participating reviews [ 9 , 10 , 12 , 13 ]. On the other hand, one research work introduces reversed phase chromatography as a suitable method for the detection and relative quantification of cereulide with common equipment in microbiological and biochemical research laboratories [ 16 ].…”