Potential enterotoxicity of phylogenetically various Bacillus cereus sensu lato soil isolates from different geographical locations

Bacillus cereus sensu lato (B. cereus s.l.) comprises gram-positive spore-forming bacteria producing toxins associated with foodborne diseases. Three pore-forming enterotoxins, non-haemolytic enterotoxin (Nhe), haemolysin BL (Hbl), and cytotoxin K (CytK), are considered as the primary factors in B. cereus s.l. diarrhoea. The aim of this study was to determine the potential risk of enterotoxicity among soil B. cereus s.l. isolates representing various phylogroups and originated from different geographic locations varying in climate (Burkina Faso, Kenya, Argentina, Kazakhstan, and Poland). While, the nheA- and hblA-positive isolates are present among all B. cereus s.l. populations and distributed across all phylogenetic groups, the cytK-2-positive strains predominate in geographic regions with arid hot climate (Africa) and clustered together on a phylogenetic tree mainly within mesophilic groups III and IV. The highest in vitro cytotoxicity to Caco-2 and HeLa cells was demonstrated by the strains clustered within phylogroups II and IV. Overall, our results suggest that B. cereus s.l. pathogenicity is a comprehensive process conditioned by many intracellular factors and diverse environmental conditions. IMPORTANCE This research offers a new route for a wider understanding of the dependency between pathogenicity and phylogeny of natural bacterial population, specifically within B. cereus s.l., that are widely distributed around the world and are easily transferred into food products. Our study indicates differences in the phylogenetic and geographical distribution of potential enterotoxigenic B. cereus s.l. strains. Hence these bacilli possess a risk for human health, rapid testing methods for their identification are greatly needed. Especially detection of the CytK enterotoxin should be a supporting strategy for the identification of pathogenic B. cereus s.l.