Exposure assessment suggests some cytotoxicBacillus cereusgroup genotypes can grow over 3 logs in HTST milk throughout the shelf life at temperature abuse conditions

Abstract

ABSTRACTCytotoxicBacillus cereusgroup strains are common causes of foodborne illness including diarrhea. However, our ability to assess food safety risks associated with the exposure to cytotoxicB. cereusgroup strainsviacontaminated food is limited due to the lack of predictive tools. In this study, we experimentally quantified the growth of 17 cytotoxicB. cereusgroup 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 105CFU/m with differentB. cereusgenotypes 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 exceedB. cereusgroup concentrations of 105CFU/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 predictedB. cereusgroup 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 lowB. cereusgroup levels.