Risk assessment of Bacillus cereus in lettuce grown in open-field and greenhouse farming systems in China: A comparative study

Objectives: Bacillus cereus isolates from vegetables can cause diarrheal syndrome food poisoning. Lettuce, the most highly consumed ready-to-eat vegetable, poses a significant risk of B. cereus exposure. Hence, B. cereus monitoring and evaluation during cultivation are essential for preventing foodborne illnesses caused by this food-pathogen combination. However, the impact of different cultivation practices on B. cereus contamination in lettuce currently remains unclear. Furthermore, a validity indicator for the experimental models cannot be effectively validated under field conditions. Materials and Methods: Herein, we assessed the risk of B. cereus exposure using lettuce grown under two different cultivation farming systems in China (open-field versus greenhouse) using a quantitative microbial risk assessment model. Tukey's mean comparison method and kernel density estimation frequency distribution statistics were used for model validation using environmental samples and lettuce. Results: The mean concentration of B. cereus in open-field-grown lettuce was significantly higher than that in greenhouse-grown lettuce (P<0.05). No significant differences were observed between measured, formula-calculated, and risk assessment values in environmental samples or lettuce (P>0.05), verifying the accuracy of the risk model. Conclusion: Soil solarization, complete manure treatment, usage of mulch films, and irrigation water quality should be considered in agricultural practices to control B. cereus concentrations in lettuce. Overall, we found that B. cereus was more abundant in open-field-grown lettuce, and we provide a risk evaluation framework that can guide farmers and policy-makers to control B. cereus contamination in farm-to-fork lettuce chains in China.