Changes in Survival and Virulence Gene Expression of Shiga Toxin-producing Escherichia coli Inoculated in Fermented Sausage

In this study, the survival of the main serotypes O157:H7 and O26:H11 of Shiga toxin-producing Escherichia coli (STEC) inoculated in fermented sausage during processing was investigated, and the changes of virulence gene expression in the bacteria and the product at different production stages were analyzed by reverse transcription real-time polymerase chain reaction (RT-real-time PCR). The results showed that there was no significant difference in the count of lactic acid bacteria, lactic acid content, pH, or water activity (a_w) value between STEC inoculated and uninoculated groups at most production stages. During sausage production, the growth of E. coli O157:H7 and O26:H11 was inhibited significantly (P < 0.05) and decreased by 1.51 and 1.39 (lg (CFU/g)), respectively, but the two strains showed different inhibition processes. After eliminating the difference in bacterial counts, it was found that the virulence gene expression in the bacterial cells was significantly up-regulated (P < 0.05) at the late stage of production. The expression of most virulence genes per unit mass of sausage increased significantly (P < 0.05) at the early stage of fermentation, and all virulence genes were highly expressed in the final product. Therefore, although STEC could be inhibited effectively during fermented sausage production, virulence gene expression was enhanced in the bacterial cells and was at a high level in the final product.