Abstract
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.
Highlights
The Bacillus cereus sensu lato group includes the following closely related spore-forming species: B. cereus sensu stricto, B. thuringiensis, B. cytotoxicus, B. weihenstephanensis, B. mycoides, B. pseudomycoides and B. anthracis [1]
B. cytotoxicus is a newly identified group of strains that induce severe food poisoning. They are characterised by the production of cytotoxin K-1 (CytK-1) and a relatively high genomic diversity compared with other B. cereus strains [1]
The aim of this study was to identify and characterise B. cereus strains from a unique national collection of 564 strains strongly related to 140 food-borne outbreaks (FBOs) that occurred in France during 2007 to 2014 in order to improve the monitoring and investigation of B. cereusinduced FBOs, assess the risk of emerging clusters of strains and identify strain variability
Summary
The Bacillus cereus sensu lato group includes the following closely related spore-forming species: B. cereus sensu stricto, B. thuringiensis, B. cytotoxicus, B. weihenstephanensis, B. mycoides, B. pseudomycoides and B. anthracis [1]. The first four species are known to be involved in food poisoning [1]. B. thuringiensis is mainly known as a biopesticide due to production of insecticidal toxins [2]. B. anthracis is highly virulent in mammals and is the causative agent of anthrax [3]. B. cytotoxicus is a newly identified group of strains that induce severe food poisoning. They are characterised by the production of cytotoxin K-1 (CytK-1) and a relatively high genomic diversity compared with other B. cereus strains [1]
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