动物源E.coli O157:H7 stx基因的检测与系统进化分析

Detection and Phylogenetic Analysis of stx Gene in Escherichia coli O157:H7 Isolated

为了解2009-2010年间在河南、甘肃地区分离鉴定的5株大肠埃希菌O157(E.coli O157)携带stx的情况及不同分离株间stx分子进化与变迁的情况,本研究利用PCR方法对分离株进行了stx基因检测,并完成了序列测定与系统演化分析。结果表明,5株不同动物源的分离株均含有stx1及stx2基因。序列分析结果显示5株分离株间stx1、stx2的核苷酸及氨基酸同源性均较高;stx1基因均与参考株中的山羊源和食品源E.coli O157菌株的同源性较高,进化树中遗传距离最近;分离株的stx2基因与多株牛源及少数人源参考株也具有较高的同源性,进化树中虽然5株分离菌均在一个大主干分支中,但分离株27与其他各分离株及参照株遗传距离最远,独自处于一次级分支中;分离株L37与W、12与50分别分布于牛源、人源E.coli O157小次级分支中;由此可推测,分离株所携带的stx1很有可能是经食品源或羊源E.coli O157传递而来;分离株L37与W、分离株12与50的stx2可能是由牛源、人源E.coli O157菌株传递而来,分离株27的stx2来源不清楚。研究结果表明,5株E.coli O157分离株均含有stx1、stx2基因,但两个基因的起源存在差异。

To investigate the germ-carrying condition, molecular evolution and transitional condition of stx in 5 Escherichia coli O157 strains which were separated and identified from Henan and Gansu province during 2009 to 2010, the stx gene of the isolated strains was amplified and sequenced, and phylogenetic analysis had been completed. The results revealed that all of the isolated strains had stxl and stx2 gene： the homology of nucleotide and amino acid of five isolated strains were high with each other; the st.rl gene of the five isolated strains showed that a high degree of omology with those referenced Escherichia coli O157 strains deprived from goat and food and their genetic distance of the cladogram are near; the stx2 gene of the isolated strains showed that a high degree of homology with those referenced Escherichia coli O157 strains deprived from cattle and hu man,though the isolated strains were in one main branch according to phylogenie trees of stx2 gene, the genetic distance of the isolated strain 27 was the farthest with other strains and only the strain 27 was in one secondary branch; the isolated strain L37 and W were in one secondary branch with the referenced strains deprived from cattle; the isolated strains 12 and 50 were in one secondary branch with the referenced strains deprived from human. We could infer from these that stxl of the five isolated strains might be Escherichia coli O157 strains deprived from food or goat; the stx2 of L37 and W might deprive from cattle, 12 and 50 might from human while 27 was not apparent. The research revealed that all the five isolated strains had stxl and stx2 gene, but the origin of the two genes were different.