Exposure assessment suggests some cytotoxic Bacillus cereus group genotypes can grow over 3 logs in HTST milk throughout the shelf life at temperature abuse conditions

Cytotoxic Bacillus cereus group strains are common causes of foodborne illness including diarrhea. However, our ability to assess food safety risks associated with the exposure to cytotoxic B. cereus group strains via contaminated food is limited due to the lack of predictive tools. In this study, we experimentally quantified the growth of 17 cytotoxic B. cereus group strains, representing six phylogenetic groups, in skim milk broth and used the growth data to develop an exposure assessment model. While none of the tested strains showed detectable growth in HTST milk at 4 or 6°C, 15 of the 17 strains showed growth at 10°C, 1 of the 17 strains showed growth at 8°C, and all strains grew at ≥14°C. Growth data for 16 strains allowed us to generate linear secondary growth models, which were then used to develop the exposure assessment model. We simulated a five-stage supply chain with up to 35 consumer storage days, as that was the timing when distinguishable variations in percent milk containers over 105 CFU/m with different B. cereus genotypes were observed. When the initial contamination level of the HTST milk is set at an average of 100 CFU/mL, the model predicts that, on consumer home storage day 21 and 35, 2.81±0.66 and 4.13±2.53 % (mean ± standard deviation) of the milk containers would exceed B. cereus group concentrations of 105 CFU/mL; these data represent the average across all strains. Sensitivity analysis showed that variation in the input parameter Q0, the initial physiological state of cells, has the largest effect on model’s prediction for 1 of 4 group II isolates, 1 of 6 group IV isolates and both group V isolates, suggesting the need to better characterize the growth parameters of these isolates. What-if scenario analysis showed that increased mean and variability in storage temperature at the consumer’s home both have substantial influence on final predicted B. cereus group concentration in milk containers. This model introduces an initial tool designed to facilitate risk-based food safety decision making for products that are contaminated with low B. cereus group levels. ### Competing Interest Statement The authors have declared no competing interest.