金黄色葡萄球菌在猪肉上的生长以及新型肠毒素基因sek的表达

The growth of Staphylococcus aureus on pork and the temporal expression of staphylococcal enterotoxin K( sek) gene

目的：研究金黄色葡萄球菌在猪肉上的生长以及新型肠毒素sek的时序性表达。方法：将实验室保存的三株携带sek基因的金黄色葡萄球菌SA005、SA008和SAB0分别接种于无菌猪肉上37℃静置培养至120 h,每隔12 h取样进行细菌计数以及p H测定,同时收集不同时间点的菌体提取RNA,利用实时荧光定量PCR监测细菌生长过程中sek的相对表达量。结果：三株菌株在猪肉上生长36 h以后进入稳定期,48 h肉上已经出现肉眼可见的金黄色葡萄球菌菌体聚集,120 h肉粒变得粘稠并有黏液渗出;猪肉p H在细菌生长的36 h前变化不大,在120 h已逐渐上升到p H8.85-9.14;三株金黄色葡萄球菌sek的表达量在细菌生长的对数期有一次高表达,随后表达量下降,在生长的稳定后期表达量再次升高,其中,SA005的sek基因在细菌的生长过程中表达量明显高于SA008和SAB0（p〈0.01）。结论：三株金黄色葡萄球菌在猪肉上生长,肠毒素sek基因持续表达但相对表达量因菌株而存在差异,sek基因在转录水平上的高表达将会带来食品安全的潜在威胁。

Objective： This study was to elucidate the growth of Staphylococcus aureus on pork and temporal expression of staphylococcal enterotoxin K（ sek） gene.Methods： Three S. aureus strains（ SA005,SA008 and SAB0）with sek gene from foodborne isolates in our lab were inoculated on pork.The growth curves and p H values change of three strains were monitored for 120 h during the growth phases on pork. Total RNAs from three strains were extracted at different time,and a quantitative real time- PCR was developed to monitor sek relative expression levels.Results： The three strains of S.aureus entered the static growth phase on pork after 36 h. Visible S. aureus bacteria gathered on pork meat around at 48 h and the pork became sticky and had mucus at 120 h.The p H values of pork did not change too much before 36 h. Until 120 h,the p H values of pork changed to 8.85 - 9.14. The sek expression levels of three strains on pork had a high- expression in exponential phase,then decreased,and later increased again.Especially,the sek expression of SA005 was obviously higher than those of SA008 and SAB0（ p〈0.01）.Conclusion： Continuous expression of sek gene in three strains on pork was observed during the whole incubation period,however,the relative expression levels of sek gene among three strains had significant differences.The high transcription levels of sek gene in S. aureus on pork would bring a potential threat on food safety.