牛源产志贺毒素大肠杆菌分离株的毒力基因分布和遗传进化分析

为了探讨牛源产志贺毒素大肠杆菌（Shiga toxin-producing Escherichia coli，STEC）分离株在毒力基因分布和遗传进化方面与人源EHEC O157菌株之间的关系，本试验选择收集来自江苏某奶牛场的STEC菌株18株以及人源、羊源、猪源、禽源STEC参考菌株9株，参照美国疾病预防控制中心PulseNet推荐的方法，运用XbaⅠ酶进行酶切并完成脉冲肠凝胶电泳（PFGE）分型和聚类分析；同时对部分STEC菌株进行毒力基因检测。结果表明，经毒力基因检测，不同来源的O157菌株毒力基因分布不尽相同，其中牛源STEC O157与参考株EHEC O157∶H7（EDL933W）的基因排谱最为相近；牛源STEC O18和O26的基因排谱与参考株EHEC O157∶H7（EDL933W）类似，但存在部分基因的缺失。对27株不同来源的STEC分离株进行PFGE，产生了22种不同的酶切图谱。总体来看，不同来源的STEC Dice相似性系数在72%~100%之间。牛源O157分离株与猪源及禽源O157菌株的相似度偏低，而与两株人源O157分离株的相似度偏高，Dice相似性系数在83%~95%之间，牛源O26（克隆群Ⅶ、Ⅷ）与人源O157的相似性系数 > 82%。显然，从牛群中分离到的部分STEC菌株与人源EHEC O157具有较近的遗传进化关系。

Study on the Virulence Gene Distribution and Genetic Evolution of Cattle Shiga Toxin-producing Escherichia coli Isolates

This study was aimed to understand the relationship of virulence gene distribution and genetic evolution between cattle originated Shiga toxin-producing Escherichia coli (STEC) and human originated enterohaemorrhagic Escherichia coli (EHEC) O157. This experiment collected 18 strains STEC in a dairy farm from Jiangsu province and 9 STEC reference strains (human, sheep, swine and avian), according to the method of U.S. Centers for Disease Prevention and Control Center (PulseNet), using the XbaⅠ enzyme digestion and pulsed field gel electrophoresis (PFGE) analysis, virulence genes were detected in some STEC isolates. The virulence gene distribution of O157 from different origin was remarkably different. The cattle originated STEC O157 and the human originated EHEC O157:H7 (EDL933W) had the most similar virulence gene distribution. In contrast, virulence genes were lack in cattle STEC O18 and O26, even though the cattle STEC O18 and O26 had the similar genotype as human EHEC O157:H7 (EDL933W). PFGE of Xba Ⅰ digested chromosomal DNA from 27 isolates of STEC exhibited 22 profiles. In general,the Dice coefficients of different originated STEC ranged from 72% to 100%.Cattle STEC O157 had a high similarity with two strains of human originated EHEC O157, while a low similarity was demonstrated between cattle STEC O157 and STEC O157 of swine and avian. The Dice coefficients of the cattle STEC O157 and the two strains of human EHEC O157 ranged from 83% to 95%. The Dice coefficients of cattle STEC O26 (Ⅶ,Ⅷ) and the two strains of human EHEC O157 were more than 82%. Therefore, it was concluded that the cattle STEC O157 and human EHEC O157 had a closer relationship in terms of virulence gene distribution and in genetic evolution.