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.

本研究详细描述了在培养介质及以谷物、乳制品、肉类和蔬菜为基础的食物基质中，枯草芽孢杆菌的生长与环状肽霉素（cereulide）的同步形成过程。首先，在9至45°C的广泛温度范围内，采用呕吐毒素参考菌株F4810/72在上述基质中进行细菌生长实验。随后，所生成数据被纳入建模框架中，其中响应变量为两个成分的向量：枯草芽孢杆菌及其毒素环状肽霉素的浓度。这两个变量均被认为是时间、温度和基质依赖性的。建模过程分为多个步骤：前一步骤中拟合的参数成为后续步骤的响应变量。通过使用平方根链接函数，利用基数参数模型（CPM）对每个基质，分别对生物体的最大比生长速率和可检测到环状肽霉素出现的时间进行建模。最后，在相同基质和多种枯草芽孢杆菌菌株中，对独立数据集进行了验证研究。结果显示，生长和毒素形成均依赖于食物基质和环境，但其依赖方式并不相同。因此，观察到枯草芽孢杆菌最高生长率的基质并非出现可检测到环状肽霉素最短时间的介质。尽管基于谷物的基质产生了最小的生长率（仅为培养介质的0.41倍），但相较于其他测试基质，其中环状肽霉素出现的时间更早。实际上，根据支持环状肽霉素形成的能力，可以将基质分为三组：（1）基于谷物的基质（最高），（2）培养介质和基于乳制品的基质（中等），以及（3）基于肉类和蔬菜的基质（最低）。这种基质间的排名与基于生物体生长适宜性的排名大相径庭。我们的模型可用于危害分析与关键控制点（HACCP）研究，以改善货架寿命预测，以及通常情况下针对以枯草芽孢杆菌为主要关注点的微生物食品安全的评估。