Table_1_Modeling Bacillus cereus Growth and Cereulide Formation in Cereal-, Dairy-, Meat-, Vegetable-Based Food and Culture Medium.DOCX

This study describes the simultaneous Bacillus cereus growth and cereulide formation, in culture medium and cereal-, dairy-, meat-, and vegetable-based food matrices. First, bacterial growth experiments were carried out under a wide range of temperatures (from 9 to 45°C), using the emetic reference strain F4810/72, in the above-mentioned matrices. Then, the generated data were put in a modeling framework where the response variable was a vector of two components: the concentration of B. cereus and that of its toxin, cereulide. Both were considered time-, temperature- and matrix-dependent. The modeling was carried out in a series of steps: the parameters fitted in one step became the response variable of the following step. Using the square root link function, the maximum specific growth rate of the organism and the time to the appearance of quantifiable cereulide were modeled against temperature by cardinal parameters models (CPM), for each matrix. Finally, a validation study was carried out on an independent data set obtained in the same matrices and using various Bacillus cereus strains. Results showed that both growth and toxin-formation depended on the food matrix and on the environment but not in the same way. Thus, the matrix (culture medium), where the highest growth rate of B. cereus was observed, was not the medium where the shortest time to quantifiable cereulide occurred. While the cereal-based matrix generated the smallest growth rates (0.41-times smaller than culture medium did), quantifiable cereulide appeared in it at earlier times compared to the other tested matrices. In fact, three groups of matrices could be distinguished based on their ability to support cereulide formation (1) the cereal-based matrix (highest), (2) the culture medium and the dairy-based matrix (intermediate), and (3) the meat- and vegetable-based matrices (lowest). This ranking between the matrices is quite different from that based on their suitability to the growth of the organism. Our models can be used in HACCP studies, to improve shelf-life predictions and, generally, microbiological food safety assessments of products for which B. cereus is the main concern.

本研究阐述了蜡样芽孢杆菌（Bacillus cereus）与呕吐毒素（cereulide）在培养基及谷物基、乳基、肉基和蔬菜基食品基质中的同步生长与合成过程。首先，采用致呕参考菌株F4810/72，在9℃至45℃的宽温度区间内，于上述各类基质中开展细菌生长实验。随后将所获数据纳入建模框架，以蜡样芽孢杆菌浓度及其毒素呕吐毒素浓度组成的二元向量作为响应变量，二者均被视为时间、温度与基质的依赖函数。建模分多阶段推进：前一阶段拟合得到的参数将作为下一阶段的响应变量。针对每种基质，分别采用基数参数模型（CPM）结合平方根连接函数，对细菌的最大比生长速率以及可检测呕吐毒素出现的时间与温度的关联关系进行建模。最后，使用在相同基质中获取的独立数据集及多株蜡样芽孢杆菌菌株开展验证研究。研究结果表明，细菌生长与毒素合成均受食品基质及环境条件影响，但二者的响应规律并不一致。例如，蜡样芽孢杆菌比生长速率最高的培养基，并非可检测呕吐毒素出现时间最短的基质。谷物基基质的比生长速率最低，仅为培养基的41%，但相较于其他受试基质，可检测呕吐毒素在其中出现的时间更早。基于基质支持呕吐毒素合成的能力，可将受试基质分为三类：(1)谷物基基质（合成能力最强）；(2)培养基与乳基基质（合成能力中等）；(3)肉基与蔬菜基基质（合成能力最弱）。该分类结果与基于蜡样芽孢杆菌生长适宜性的基质排序存在显著差异。本研究构建的模型可应用于危害分析与关键控制点（HACCP）研究，以优化食品货架期预测，并可普遍用于以蜡样芽孢杆菌为主要安全隐患的食品微生物安全性评估。