Predicting B. cereus growth and cereulide production in dairy mix

Assessment of the exposure to cytotoxic Bacillus cereus group genotypes through HTST milk consumption

This study addresses the limited tools available for assessing food safety risks from cytotoxic Bacillus cereus group strains in contaminated food. We quantified the growth, in skim milk broth, of 17 cytotoxic B. cereus strains across 6 phylogenetic groups with various virulence gene profiles. The strains did not grow in HTST milk at 4 or 6°C. At 10°C, 15 strains exhibited growth; at 8°C, one strain grew; and all strains grew at temperatures ≥ 14°C. Using growth data from 16 strains, we developed linear secondary growth models and an exposure assessment model. This model, simulating a 5-stage HTST milk supply chain and up to 35 d of consumer storage with an initial contamination of 100 cfu/mL, estimated that 2.81 ± 0.66% and 4.13 ± 2.53% of milk containers would surpass 105 cfu/mL of B. cereus by d 21 and 35, respectively. A sensitivity analysis identified the initial physiological state of cells (Q0) as the most influential variable affecting predictions for specific isolates. What-if scenarios indicated that increases in mean and variability of consumer storage temperatures significantly affected the predicted B. cereus concentrations in milk. This model serves as an initial tool for risk-based food safety decision making regarding low-level B. cereus contamination.

The potential of lactose to inhibit cereulide biosynthesis of emetic Bacillus cereus in milk

This study aims to investigate the potential role of lactose on cereulide biosynthesis by emetic Bacillus cereus in dairy matrices. The cereulide yields in whole milk and lactose-free milk were investigated using the emetic reference strain F4810/72. To eliminate the influence of complex food substrates, the LB medium model was further used to characterize the effect of lactose on cereulide produced by F4810/72 and five other emetic B. cereus strains. Results showed that the lactose-free milk displayed a 13-fold higher amount of cereulide than whole milk, but the cereulide level could be reduced by 91 % when the lactose content was restored. The significant inhibition of lactose on cereulide yields of all tested B. cereus strains was observed in LB medium, showing a dose-dependent manner with inhibition rates ranging of 89-98 %. The growth curves and lactose utilization patterns of all strains demonstrated that B. cereus cannot utilize lactose as a carbon source and lactose might act as a signal molecule to regulate cereulide production. Moreover, lactose strongly repressed the expression of cereulide synthetase genes (ces), possibly by inhibiting the key regulator Spo0A at the transcriptional level. Our findings highlight the potential of lactose as an effective strategy to control cereulide production in food.

Modelling growth of Bacillus cereus in paneer by one-step parameter estimation

Bacillus cereus phylogenetic group III and IV strains are commonly associated with food products and cause toxin mediated foodborne diseases. These pathogenic strains have been identified from milk and dairy products, such as reconstituted infant formula and several cheeses. Paneer is a fresh, soft cheese originating from India that is prone to foodborne pathogen contamination, such as by Bacillus cereus. However, there are no reported studies of B. cereus toxin formation in paneer or predictive models quantifying growth of the pathogen in paneer under different environmental conditions. This study assessed enterotoxin-producing potential of B. cereus group III and IV strains, isolated from dairy farm environments, in fresh paneer. Growth of a four-strain cocktail of toxin-producing B. cereus strains was measured in freshly prepared paneer incubated at 5-55 °C and modelled using a one-step parameter estimation combined with bootstrap re-sampling to generate confidence intervals for model parameters. The pathogen grew in paneer between 10 and 50 °C and the developed model fit the observed data well (R² = 0.972, RMSE = 0.321 log₁₀ CFU/g). The cardinal parameters for B. cereus growth in paneer along with the 95% confidence intervals were: μ_opt 0.812 log₁₀ CFU/g/h (0.742, 0.917); T_opt is 44.177 °C (43.16, 45.49); T_min is 4.405 °C (3.973, 4.829); T_max is 50.676 °C (50.367, 51.144). The model developed can be used in food safety management plans and risk assessments to improve safety of paneer while also adding to limited information on B. cereus growth kinetics in dairy products.