Shanghai Food Research Institute, Shanghai 200235, China.
Shanghai Municipal Center for Disease Control and Prevention, Shanghai 200336, China.
Food Res Int. 2021 May;143:110298. doi: 10.1016/j.foodres.2021.110298. Epub 2021 Mar 9.
Numerous studies on bacterial growth or survival predictive models have been conducted since the establishment of predictive microbiology. However, limited research focused on the prediction of bacteria-producing enterotoxins, which are often the causative agents of food-borne diseases. This study aimed to determine an appropriate kinetic model of staphylococcal enterotoxin A (SEA) production in milk after contamination with Staphylococcus aureus. An S. aureus strain producing SEA was inoculated into milk with an initial inoculum concentration of approximately 3.0 log CFU/mL. All samples were incubated for 30-48 h at 20 °C ± 1 °C, 28 °C ± 1 °C, and 36 °C ± 1 °C separately under shaking or static conditions. Duplicate samples were carried out at appropriate intervals to count the number of S. aureus colonies and detect the concentration of SEA. Experimental results showed that the SEA concentration curves under all experimental conditions were sigmoidal and consisted of three phases: lag, exponential, and stationary. Thus, the modified Gompertz model was used to describe the profile of SEA concentration in milk during the incubation. A good fitting accuracy (R > 0.97) indicated that the modified Gompertz model was appropriate. In addition to temperature, shaking during incubation also affected the maximal production rate of SEA and the maximal SEA concentrations, and shortened the lag phase at lower incubation temperatures, suggesting that the mechanical movements (e.g., stirring, pumping, and flowing) during the milk processing would increase the risk of SEA occurrence. Besides, the time to detection (TTD) of SEA was found to range from 3 to 24.5 h at temperatures of 36 °C ± 1 °C-20 °C ± 1 °C, at which time the concentrations of S. aureus ranging from 5.0 log CFU/mL-6.9 log CFU/mL at the TTD. This study contributed to understanding the kinetics of SEA production and the possible factors affecting the synthesis of SEA during the manufacturing of liquid foods, such as milk.
自预测微生物学建立以来，已经有许多关于细菌生长或存活预测模型的研究。然而，很少有研究关注于预测产肠毒素细菌，而这些细菌通常是食源性疾病的病原体。本研究旨在确定金黄色葡萄球菌（S. aureus）污染牛奶后金黄色葡萄球菌肠毒素 A（SEA）产生的合适动力学模型。将产 SEA 的 S. aureus 菌株以约 3.0 log CFU/mL 的初始接种浓度接种到牛奶中。所有样品在 20°C±1°C、28°C±1°C 和 36°C±1°C 下分别在摇床或静置条件下孵育 30-48 h。在适当的时间间隔进行重复样品以计数 S. aureus 菌落的数量并检测 SEA 的浓度。实验结果表明，所有实验条件下的 SEA 浓度曲线均呈 S 形，分为三个阶段：迟滞期、指数生长期和稳定期。因此，采用修正的 Gompertz 模型来描述 SEA 浓度在培养过程中牛奶的浓度曲线。较高的 R 值（R>0.97）表明修正的 Gompertz 模型是合适的。除温度外，培养过程中的振荡也影响 SEA 的最大产率和最大 SEA 浓度，并缩短了较低培养温度下的迟滞期，这表明牛奶加工过程中的机械运动（如搅拌、泵送和流动）会增加 SEA 发生的风险。此外，SEA 的检测时间（TTD）在 36°C±1°C-20°C±1°C 的温度范围内从 3 小时到 24.5 小时不等，此时 TTD 处的 S. aureus 浓度在 5.0 log CFU/mL-6.9 log CFU/mL 之间。本研究有助于了解 SEA 产生的动力学以及在液体食品（如牛奶）的制造过程中可能影响 SEA 合成的因素。
