Abstract
Bacillus cereus sensu lato comprises Gram-positive spore-forming bacteria producing toxins associated with foodborne diseases. Three pore-forming enterotoxins, nonhemolytic enterotoxin (Nhe), hemolysin BL (Hbl), and cytotoxin K (CytK), are considered the primary factors in B. cereus sensu lato diarrhea. The aim of this study was to determine the potential risk of enterotoxicity among soil B. cereus sensu lato isolates representing diverse phylogroups and originated from different geographic locations with various climates (Burkina Faso, Kenya, Argentina, Kazakhstan, and Poland). While nheA- and hblA-positive isolates were present among all B. cereus sensu lato populations and distributed across all phylogenetic groups, cytK-2-positive strains predominated in geographic regions with an 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 sensu lato 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 a natural bacterial population, specifically within Bacillus cereus sensu lato, that is widely distributed around the world and easily transferred into food products. Our study indicates differences in the phylogenetic and geographical distributions of potential enterotoxigenic B. cereus sensu lato strains. Hence, these bacilli possess a risk for human health, and rapid testing methods for their identification are greatly needed. In particular, the detection of the CytK enterotoxin should be a supporting strategy for the identification of pathogenic B. cereus sensu lato.
Highlights
Bacillus cereus sensu lato comprises Gram-positive spore-forming bacteria producing toxins associated with foodborne diseases
Among 1,012 B. cereus sensu lato isolates originating from soil samples obtained from geographically different locations (Fig. 1, with a map adapted from Peel and coworkers [39]), the cytK gene was present in 40.6% of the isolates
Cytotoxic Potential of Bacillus cereus Sensu Lato population, while the cytK-2-positive strains were noted in the highest proportion in Kenyan bacilli from Tsavo East National Park and Shimba Hills National Reserve (91.9%) as well as among Burkinabe isolates from an urban park in Ouagadougou (60.0%), followed by Argentinian strains from a soil sample taken in a park in Buenos Aires (38.3%) and Kazakh bacilli from a park in Almaty (28.0%)
Summary
Bacillus cereus sensu lato comprises Gram-positive spore-forming bacteria producing toxins associated with foodborne diseases. The aim of this study was to determine the potential risk of enterotoxicity among soil B. cereus sensu lato isolates representing diverse phylogroups and originated from different geographic locations with various climates (Burkina Faso, Kenya, Argentina, Kazakhstan, and Poland). As Guinebretière and coworkers [38] showed that food poisoning potential appeared to correlate with phylogenetic groups and different distributions for emetic and diarrheal disease are observed between countries [25], we assumed that B. cereus sensu lato strains from an individual geographic location group together into different thermal phylogenetic groups that possess various enterotoxic potentials. The goal of this study was to determine the potential risk of enterotoxicity among soil populations representing various phylogroups and originating from different geographic locations with varied climates, including arid hot steppe (Burkina Faso, Kenya), wet savanna (Kenya), a mild climate with hot summers (Argentina), and continental cold climates with hot (Kazakhstan) and warm (Poland) summers
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