Metabolic capacities and toxigenic potential as key drivers of Bacillus cereus ubiquity and adaptation

Bacillus cereus is ubiquitous and commonly found in a wide range of environments,including food. In this study, we analysed 114 foodborne B. cereus strains isolated mainly from starchy and dairy products in order to investigate their phenotypic diversity (API system), antimicrobial resistance and toxigenic profiles (hblA, nheA, hlyII,cereolysin O, cytK2, cytK1 and EM1 genes). All isolates were confirmed as B. cereus using 16S-23S ribosomal DNA intergenic transcribed spacers (ITS) signature. They were shown as Gram-positive, catalase and caseinase positive, haemolytic (97%), and positive for lecithin hydrolysis and motility (97 and 87 %, respectively). PCR detection of the B. cereus specific toxin genes revealed the occurrence rates of 100 % for cereolysin O, 98 % for nheA, 74 % for cytk2, 52 % for hblA, 28 % for hlyII, and the absence of cytK1. Only two strains (1.75%), isolated from intestine of boar and pheasant, carried the emetic toxin genetic determinants (ces). Antimicrobial susceptibility of isolates was tested towards 15 different antimicrobial agents. We detected susceptibility of all strains to most antibiotics, intermediate resistance to clindamycin and resistance to β lactam antibiotics with 83% of the resistant isolates producing β lactamase enzyme. This large phenotypic diversity combined with the toxigenic traits and antibiotic resistance; emphasize the high potential risk of food poisoning of B. cereus isolates. Beside, a clear correlation between the metabolic features and the origin of isolation was shown. Most of starchy isolates were able to hydrolyse starch while dairy strains were not able to produce amylases. Our overall results point out that the metabolic flexibility and toxigenic potential represent the main drivers for B. cereus ubiquity and adaptation in a given ecological nich