Occurrence, persistence and pathogenic potential of Bacillus cereus sensu lato strains isolated during processing of...

Ensuring the microbiological safety of plant-based foods is challenging, particularly during the development of new products. This study aimed to map and identify Bacillus cereus sensu lato (s.l.) contaminants during the production of two plant-based desserts: one fermented and one non-fermented, in order to identify critical processing stages. A bacterial survey was conducted along the processing line of each dessert and 120 product samples were collected from raw materials, processing stages, and during product storage. Total bacterial counts ranged from <2.0 to 10.1 Log₁₀ CFU/g during processing while mesophilic spore counts varied between <2.0 and 2.5 ± 0.7 Log₁₀ CFU/g. Thermophilic and B. cereus s.l. spores remained below the detection limit (2.0 Log₁₀ CFU/g). A selective enrichment demonstrated that B. cereus s.l. was present during all steps of both processes. In total, 127 isolates were recovered from ingredients, processing steps and conditioned products. Analysis assigned these isolates to phylogenetic groups II, III, IV and VII, with group IV strains being the most prevalent. Several strains persisted throughout processing, indicating their resilience to technological treatments. Approximately 60 % of the isolates carried the enterotoxin gene combination hbl-nhe-cytK, whereas the emetic ces gene was detected only once. B. cereus s.l. growth was observed in the non-fermented dessert when storage temperatures reached 10 °C during 20 days, but no growth was detected in the fermented product. These findings provide insights into contamination pathways and the persistence of B. cereus s.l. during processing, which will help to design safe processing conditions for plant-based dairy alternatives.