Abstract：
Staphylococcal enterotoxins (SEs) secreted by Staphylococcus aureus (S. aureus) can cause foodborne disease, nausea, vomiting and diarrhea, and even death. Regulation of SE expression is related to accessory gene regulators (Agr). It is important to reveal which environmental factors influence regulation of SE expression to prevent SE food poisoning outbreak. Hence, natural environmental factors which may have an impact on SE expression were selected, such as temperature, food types, strains, and competing strains. Seven strains of S. aureus carrying different SE genes were collected from the Chinese Academy of Inspection and Quarantine (CAIQ) strain bank for study. Strains were cultured with different conditions. Temperature was 8 °C, 22 °C, and 30 °C. Food type was milk powder and nutrient broth. Competing strains were Vibrio parahaemolyticus (V. parahaemolyticus), Escherichia coli (E. coli), and Bacillus cereus (B. cereus). The expression culture solution was pretreated by centrifugation, then determined by using SDS-PAGE, and distinguished SEs apart from each other by HPLC-ESI-TOF. There are 168 samples collected from SE expression culture; the result of SDS-PAGE suggests 23 samples were positive for SEs, and the other 145 samples were negative for SEs. The result of HPLC-ESI-TOF suggests that SEs with similar molecular weight can be distinguished in terms of m/z. The most important factor contributing to regulate expression of SEs was estimated by logistic regressive analysis. The result shows that McFadden R2 is 0.213; p value is 0.000 (p < 0.05); this result illustrates that the model is valid and meaningful. Strains, food types, temperature, and competing strands can explain the 21% change in SE expression. Temperature (z = 3.029, p = 0.002 < 0.01), strains (z = - 3.132, p = 0.002 < 0.01), and food types (z = - 2.415, p = 0.016 < 0.05) have significant impact on SE expression, and the competing strains (z = 1.230, p = 0.219 > 0.05) have no impact on the SE expression. More important impact on SE expression was estimated by OR value; the result shows that strength of temperature influencing on SE expression is bigger than strains and food types in terms of values of OR, temperature (OR = 2.862), strains (OR = 0.641), and food types (OR = 0.561); consequently, temperature is a key factor for stimulating SE expression and had high expression at 30 °C. Therefore, food easily contaminated with S. aureus should be monitored intensively at early and late summer, when proper temperature for expressing SEs may result in S. aureus food poisoning prevalence.
摘要：
金黄色葡萄球菌分泌的葡萄球菌肠毒素（SE）（S.金黄色葡萄球菌)可引起食源性疾病，恶心,呕吐和腹泻,甚至死亡。SE表达的调节与辅助基因调节因子(Agr)有关。揭示哪些环境因素会影响SE表达的调节，以防止SE食物中毒的爆发。因此，选择可能对SE表达有影响的自然环境因子，如温度，食物种类,菌株，和竞争菌株。从中国检验检疫科学研究院（CAIQ）菌株库收集了7株携带不同SE基因的金黄色葡萄球菌进行研究。菌株在不同条件下培养。温度为8°C,22°C,和30°C。食物类型为奶粉和营养肉汤。竞争菌株为副溶血性弧菌(V.副溶血病），大肠杆菌(E.大肠杆菌)，和蜡样芽孢杆菌(B.cereus).表达培养液经离心预处理,然后用SDS-PAGE测定，并通过HPLC-ESI-TOF区分SE。从SE表达培养物中收集了168个样品；SDS-PAGE结果表明23个样品对SE呈阳性，其他145份样本均为SE阴性。HPLC-ESI-TOF的结果表明,具有相似分子量的SE可以在m/z方面进行区分。通过逻辑回归分析估计了调节SEs表达的最重要因素。结果表明，McFaddenR2为0.213；p值为0.000（p<0.05）；该结果表明该模型是有效和有意义的。菌株,食物种类,温度,竞争链可以解释SE表达的21%变化。温度(z=3.029,p=0.002<0.01),应变（z=-3.132，p=0.002<0.01），和食物类型（z=-2.415，p=0.016<0.05）对SE表达有显著影响，竞争菌株(z=1.230,p=0.219>0.05)对SE表达没有影响。通过OR值估计对SE表达的影响更重要。结果表明，就OR值而言，温度对SE表达的影响强度大于菌株和食物类型。温度（OR=2.862），菌株(OR=0.641)，和食物类型(OR=0.561)；因此，温度是刺激SE表达的关键因素，在30℃时具有高表达。因此,容易被金黄色葡萄球菌污染的食物应在夏初和夏末进行集中监测，当表达SE的适当温度时，可能会导致金黄色葡萄球菌食物中毒的流行。
