肠出血性大肠埃希菌O157∶H7新接合质粒pO157_SalTraE序列分析

Sequence analysis of TraE in the novel conjugative plasmid pO157_Sal detected in Escherichia coli O157∶H7

目的：分析我国肠出血性大肠埃希菌 O157∶H7暴发菌株携带的新接合质粒 pO157_Sal的序列特征。方法对我国不同来源携带 pO157_Sal 的大肠埃希菌 O157∶H7暴发菌株进行 traE 基因PCR 扩增、克隆测序，并在 GenBank 中比对检索其他来源大肠埃希菌 O157∶H7菌株的 TraE 序列，以邻接法构建基于 TraE 序列的系统发生树；在全质粒序列水平比较分析 pO157_Sal 与 pEC4115。结果我国不同宿主来源的暴发菌株携带的 traE 基因序列完全相同；pO157_Sal TraE 的相似性序列存在于不同国家不同宿主来源及不同分离年代的大肠埃希菌 O157∶ H7分离株中；pO157_Sal 中21个基因与pEC4115质粒编码的基因存在28％～51％的氨基酸相似性。结论虽然不同来源的大肠埃希菌O157∶H7菌株中存在相似性 TraE 序列或相似质粒 pEC4115，但 pO157_Sal 为我国暴发菌株所特有，其序列在暴发菌株间保守，提示其为特定的相同来源。

Objective To analyze the sequence of the novel conjugative plasmid pO157_Sal detected in outbreak isolates of Escherichia coli O157∶H7 .Methods The traE genes of the outbreak isolates in China were amplified by polymerase chain reaction （PCR） and the products were sequenced .The TraE sequences of Escherichia coli O157 ∶ H7 strains from other sources were retrieved from GenBank . Phylogenetic tree based on the TraE sequences was constructed by Neibhor-joining analysis .The whole plasmid sequences of pO157_Sal and pEC4115 were compared .Results The sequences of traE gene were identical among the Chinese isolates . There were homologous sequences of TraE in Escherichia coli O157∶H7 isolates from different sources .Twenty-one out of the 52 pO157_Sal genes were homologous to genes of pEC4115 with amino acid level identity ranging from 28% to 51% .Conclusions Although similar TraE sequences and similar plasmid are found in Escherichia coli O157∶H7 isolates from different sources ,pO157_Sal is only observed in Chinese outbreak isolates .The TraE sequences are conservative among the outbreak isolates ,indicating they are from the same specific source .