发酵香肠中产志贺毒素大肠杆菌存活和毒力基因表达变化

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

以产志贺毒素大肠杆菌(Shiga toxin-producing Escherichia coli,STEC)主要血清型O157:H7和O26:H11为实验菌,进行发酵香肠接种实验,研究发酵香肠生产过程中这两种菌的存活情况,并采用反转录实时聚合酶链式反应(reverse transcription real-time polymerase chain reaction,RT-real-time PCR)的绝对定量方法分析不同生产阶段菌体和产品中毒力基因表达变化。结果显示:STEC接种组与未接种组之间乳酸菌数、乳酸含量、pH值、a_(w)值在大多生产阶段无显著差异。香肠生产过程中大肠杆菌O157:H7和O26:H11存活菌数分别减少了1.51(lg(CFU/g))和1.39(lg(CFU/g)),均受到显著抑制(P<0.05),但两菌呈现出不一样的受抑制过程。采用RT-real-time PCR绝对定量,消除菌数差异后发现菌体毒力基因表达在生产后期均显著上调(P<0.05);单位质量香肠中大多毒力基因表达量在发酵初期显著增加(P<0.05),且所有毒力基因在生产末期终产品中仍有较高表达量。本研究表明:虽然发酵香肠生产过程中能有效抑制STEC,但却增强了菌体毒力基因的表达,且终产品中毒力基因存在较高表达量。

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.