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The aim of this study was to identify and characterise Bacillus cereus from a unique national collection of 564 strains associated with 140 strong-evidence food-borne outbreaks (FBOs) occurring in France during 2007 to 2014. Starchy food and vegetables were the most frequent food vehicles identified; 747 of 911 human cases occurred in institutional catering contexts. Incubation period was significantly shorter for emetic strains compared with diarrhoeal strains A sub-panel of 149 strains strictly associated to 74 FBOs and selected on Coliphage M13-PCR pattern, was studied for detection of the genes encoding cereulide, diarrhoeic toxins (Nhe, Hbl, CytK1 and CytK2) and haemolysin (HlyII), as well as panC phylogenetic classification. This clustered the strains into 12 genetic signatures (GSs) highlighting the virulence potential of each strain. GS1 (nhe genes only) and GS2 (nhe, hbl and cytK2), were the most prevalent GS and may have a large impact on human health as they were present in 28% and 31% of FBOs, respectively. Our study provides a convenient molecular scheme for characterisation of B. cereus strains responsible for FBOs in order to improve the monitoring and investigation of B. cereus-induced FBOs, assess emerging clusters and diversity of strains.

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Aims: This paper provides information on a PCR-ELISA method for detecting Shiga toxinproducing Escherichia coli (STEC), and on their prevalence in dairy products. Methods and Results: The sensitivity and speci®city of the test was evaluated using pure cultures, spiked and naturally-contaminated samples. A comparative study with vero cytotoxicity testing was conducted, and STEC isolated from naturally-contaminated 1 samples were characterized. The PCR-ELISA test was highly speci®c and sensitive, and detected 14% more positive samples than the vero cell assay. The prevalence of STEC in raw milk and unpasteurized cheese was 21á5% and 30á5%, respectively, while samples from the`dairy environment' and from pasteurized cheese were less contaminated. The 34 strains of STEC isolated from natural samples showed that some of them carried virulence genes. Conclusions: No conclusion can be drawn at the moment concerning the potential risk to consumers. Signi®cance and Impact of the Study: These data show the necessity of valuable screening methods to appreciate the virulence of STEC.