Bacillus cereus (B. cereus) group species consist of large, sporulating, Gram-positive, and rod-shaped aerobic or facultative anaerobic bacteria that are widespread in the environment. These bacteria can be isolated from their environmental reservoir: soil, sea sediments and seawater, plants, and carcasses of animals[1, 2]. These bacterial species are known to have a significant impact on human health, agriculture, or food industry, especially B. anthracis, B. cereus sensu stricto, and B. thuringiensis[1].
B. cereus sensu stricto can contaminate food, especially vegetables and starchy food, and is mainly involved in gastrointestinal infections in humans. It represents one of the major causes of food poisoning outbreaks in Europe[3]. To date, literature has reported 22 species closely related to B. cereus sensu stricto[4]. However, distinguishing B. cereus sensu stricto and the other members of the group using routine phenotypic identification methods in the clinical microbiology laboratory is challenging. Consequently, not all invasive infections attributed to B. cereus are necessarily caused by B. cereus sensu stricto; they could be due to other closely related species within the B. cereus group.
There are two types of food poisoning due to B. cereus, which differ in terms of symptoms and origin, known as the emetic and the diarrheal syndromes[5, 6]. The emetic syndrome results from an intoxication provoked by the emetic toxin cereulide, a toxin often pre-formed in food before ingestion[7]. This toxin causes nausea and vomiting that occur quickly (between 30 min and 6 h after ingestion) and has been linked to severe clinical forms associated with fatalities, in particular, because of liver failure[8]. The diarrheal syndrome is associated with the production of enterotoxins in the small intestine following the ingestion of contaminated food. These toxins include nonhemolytic toxin (Nhe; encoded by nheABC), hemolysin BL (Hbl; encoded by hblCDA), and cytotoxin K (CytK; encoded by cytK-2 or B. cytotoxicus gene variant cytK-1)[9]. Bacteria can be ingested as vegetative cells or as spores, which once in the intestine, germinate, multiply, and produce enterotoxins[10]. Symptoms appear 5 h to 24 h after ingestion, and manifest through abdominal pain and profuse diarrhea[11]. Manifestations are generally mild with spontaneous remission within 24 h without any treatment. However, fatal cases resulting for example from necrotic enteritis have been reported[12].
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