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

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.