牛源性大肠杆菌O157:H7的分离鉴定及其耐酸性比较研究

为比较大肠杆菌（Escherichia coli）O157:H7产毒菌株耐受盐酸和乳酸的差异性，首先采集309 份牛粪及牛肉样，进行菌株分离鉴定，接着采用多重聚合酶链式反应（polymerase chain reaction，PCR）方法检测分离株及其他收集菌株的4 种毒力基因（eae、hly、stx1、stx2），进而对携带毒力基因的产毒菌株分别进行盐酸和乳酸应激实验。结果表明：共分离鉴定出8 株大肠杆菌O157菌株，样品阳性检出率为2.59%；毒力基因检测表明，8 株菌株均不携带stx1和stx2基因，其中6 株菌株携带eae及hly基因；所有产毒菌株耐酸性实验结果表明，盐酸或乳酸处理2 h后20 株产毒菌株存活菌数均显著下降（P＜0.05），但下降程度呈现明显的菌株差异性，同一菌株对盐酸、乳酸呈现明显的耐受差异。

Isolation and Identification of Escherichia coli O157:H7 from Cattle and Comparison of Their Acid Tolerance

To investigate the variability of the tolerance of Shiga toxin-producing Escherichia coli O157:H7 to hydrochloric acid and lactic acid, suspected colonies were isolated from 309 fecal and beef samples and identified in this study. The isolates and another 14 strains collected for this study were detected for 4 major virulence genes (eae, hly, stx1, stx2) by multiplex polymerase chain reaction, and each of the Shiga toxin-producing strains with virulence genes was separately exposed to hydrochloric acid and lactic acid stress. The results showed that 8 isolates of E. coli O157 were identified and the prevalence of positive samples was 2.59%. The results of virulence genes showed that the stx1 and stx2 genes were detected in none of the 8 strains and the eae and hly genes were detected in 6 of them. The results of acid tolerance showed that the survival rates of 20 Shiga toxin-producing strains including the 6 strains and the other 14 above were all significantly decreased (P < 0.05) after treatment with hydrochloric acid or lactic acid for 2 h. However, this effect varied between strains, and the tolerance of the same strain to different acid treatments was different.