Emetic Bacillus cereus are more volatile than thought: recent foodborne outbreaks and prevalence studies in Bavaria (2007-2013).

Several Bacillus cereus strains possess the genetic fittings to produce two different types of toxins, the heat-stable cereulide or different heat-labile proteins with enterotoxigenic potential. Unlike the diarrheal toxins, cereulide is (pre-)formed in food and can cause foodborne intoxications shortly after ingestion of contaminated food. Based on the widely self-limiting character of cereulide intoxications and rarely performed differential diagnostic in routine laboratories, the real incidence is largely unknown. Therefore, during a 7-year period about 4.300 food samples linked to foodborne illness with a preliminary report of vomiting as well as food analysed in the context of monitoring programs were investigated to determine the prevalence of emetic B. cereus in food environments. In addition, a lux-based real-time monitoring system was employed to assess the significance of the detection of emetic strains in different food matrices and to determine the actual risk of cereulide toxin production in different types of food. This comprehensive study showed that emetic strains are much more volatile than previously thought. Our survey highlights the importance and need of novel strategies to move from the currently taxonomic-driven diagnostic to more risk orientated diagnostics to improve food and consumer safety.

Identification of the main promoter directing cereulide biosynthesis in emetic Bacillus cereus and its application for real-time monitoring of ces gene expression in foods.

Cereulide, the emetic Bacillus cereus toxin, is synthesized by cereulide synthetase via a nonribosomal peptide synthetase (NRPS) mechanism. Previous studies focused on the identification, structural organization, and biochemical characterization of the ces gene locus encoding cereulide synthetase; however, detailed information about the transcriptional organization of the ces genes was lacking. The present study shows that the cesPTABCD genes are transcribed as a 23-kb polycistronic transcript, while cesH, encoding a putative hydrolase, is transcribed from its own promoter. Transcription initiation was mapped by primer extension and rapid amplification of cDNA ends (RACE). Deletion analysis of promoter elements revealed a main promoter located upstream of the cesP coding sequence, encoding a 4'-phosphopantetheinyl transferase. This promoter drives transcription of cesPTABCD. In addition, intracistronic promoter regions in proximity to the translational start sites of cesB and cesT were identified but were only weakly active under the chosen assay conditions. The identified main promoter was amplified from the emetic reference strain B. cereus F4810/72 and fused to luciferase genes in order to study promoter activity in complex environments and to establish a biomonitoring system to assess cereulide production in different types of foods. ces promoter activity was strongly influenced by the food matrix and varied by 5 orders of magnitude. The amount of cereulide toxin extracted from spiked foods correlated well with the bioluminescence data, thus illustrating the potential of the established reporter system for monitoring of ces gene expression in complex matrices.