Occurrence of selected bacterial pathogens in insect-based food products and in-depth characterisation of detected Bacillus cereus group isolates

Insects are increasingly used as alternative protein sources and ingredients of foodstuffs produced in industrial scale. Previous studies on the microbial status of insect-based foods revealed that classical foodborne pathogens such as Salmonella spp., Campylobacter spp., Listeria monocytogenes or pathogenic Escherichia coli are rarely detected, whereas particularly spore-forming bacteria with pathogenic potential such as species of the Bacillus cereus group or Clostridium species may pose a food safety risk. However, detailed descriptions of the encountered pathogenic bacteria in insect foods are scarce. We investigated a variety of 73 food products with insect or other arthropod ingredients on the occurrence of potential bacterial pathogens. These included B. cereus (sensu lato (s.l.)), Clostridium perfringens and Clostridioides difficile as representatives of spore-formers and Salmonella spp. and Shiga toxin producing and enteropathogenic E. coli (STEC/EPEC) as representatives of non-spore-forming Enterobacteriaceae. Most of the investigated food products complied with food safety standards regarding the presence of pathogens considered. However, one cricket product contained two Salmonella enterica subspecies enterica serovars (S. Wandsworth and S. Stanley). B. cereus (s.l.) was found in 42 samples (58 %), of which six contained B. cereus (s.l.) at levels higher than 10³ cfu/g. The highest B. cereus (s.l.) counts of 3.8 × 10⁵ cfu/g were found in a product with boiled and dried scorpions. Clostridium perfringens was detected in twelve samples (16 %), whereas Clostridioides difficile and STEC/EPEC were not detected in any of the samples. Remarkably, five samples contained the B. cereus (s.l.) species B. cytotoxicus. Moreover, strikingly high numbers of B. cereus (s.l.) isolates carried the capsule syntheses genes capBCADE, which were presumably located on the B. cereus pBFI_2 plasmid. Whole genome sequencing-based phylogenetic analysis suggested a high relatedness for only very few of the B. cytotoxicus and cap-positive isolates, respectively.