Investigation of Bacillus cereus growth and sporulation during Hermetia illucens larval rearing

Insects are increasingly used as an alternative protein source for feed and food production. One of the main biological hazards associated with edible insects is the bio-accumulation of foodborne pathogenic microorganisms. In this study, the interaction of larvae of the black soldier fly (BSFL, <i>Hermetia illucens</i> (L.), Diptera: Stratiomyidae) with the foodborne pathogen <i>Bacillus cereus</i> was explored. As such, BSFL were reared on a substrate of wheat-based insect feed mixed with water, which was inoculated with either <i>B. cereus</i> vegetative cells or endospores<i>.</i> After seven days of rearing, the larvae and the residual substrate (frass) were analyzed for the presence of <i>B. cereus</i>, phenotypically via classical microbial counting and genotypically via real-time PCR. Endospores were detected on a selective growth medium in the larvae as well as in the frass. An additional heating step (1 min at 100 °C) to mimic blanching did not reduce the microbial count of the endospores. Results show that <i>B. cereus</i> endospores can be transferred to larvae. It is therefore recommend that substrate ingredients for BSFL rearing are tested for the presence of <i>B. cereus</i> endospores.