Abstract: To investigate the effects of salt stress at different levels on the survival and virulence gene expression of Escherichia coli O157:H7, as well as the correlation between them, three virulent strains (CICC21530, 95 and 109) collected in our lab were cultured separately in trypticase soy broth medium with different concentrations of NaCl (0, 6, 12 and 18 g/100 mL) for differnent time periods. Afterwards, each strain was enumarated, and the expression levels of virulence genes were detected by real-time polymerase chain reaction. Results showed that salt stress significantly decreased the survival of the three strains (P < 0.05), but the effect varied among these strains. Higher concentration of NaCl was associated with stronger inhibitory effects on strain CICC21530, while the survival of strains 95 and 109 were fluctuated. In addition, the expression levels of virulence genes in E. coli O157:H7 were related to strains and NaCl addition. At higher NaCl concentration, the expression levels of virulence genes in all strains increased significantly (P < 0.05) accompanied by a significant decrease in the survival rate. The highest expression levels of virulence genes were observed in strains CICC21530 and 95 at 18 g/100 mL NaCl concentration, and in strain 109 at 12 g/100 mL. These results suggested that the survival of E. coli O157:H7 strains were not completely consistent with the expression of virulence genes under salt stress, and the survival decreased while the expression levels of virulence genes increased. It is indicated that the survival of strains and the expression level of virulence genes should be simultaneously considered in the risk assessment of salty foods, which is beneficial for the scientific and comprehensive risk assessment of E. coli O157:H7.

Key words: Escherichia coli O157:H7; salt stress; survival; expression of virulence genes