不同来源产志贺毒素2e亚型大肠埃希菌分子特征分析

Molecular characteristics of Escherichia coli strains producing Shiga toxin 2e subtype from different sources

目的了解我国不同来源产志贺毒素stx2e亚型大肠埃希菌分离株的分子特征。方法对2012年—2018年间监测中发现的3株人源、13株动物源及8株食品来源的携带stx2e基因亚型的大肠埃希菌进行体外抗生素敏感性试验并进行全基因组测序。根据全基因组序列,对菌株stx基因亚型、血清型、多位点序列分型(MLST)、毒力基因及耐药基因携带情况、系统进化关系及志贺毒素前噬菌体基因组成进行分析。结果24株菌分为19种O∶H血清型和19种序列(ST)型,均携带至少1种耐药相关基因,其中19株菌至少对一种抗生素耐药。3株人源菌株分别属于不同血清型及ST型,但存在与之相同血清型或ST型的动物、食品来源菌株;全基因组进化分析显示相同血清型或ST型的人源菌株分别与动物或食品源菌株具有较近亲缘关系。不同菌株间stx2e序列高度相似(>99.7%),但志贺毒素前噬菌体基因组成、大小等存在较大差异。结论本研究为我国对罕见的人源性stx2e亚型大肠埃希菌菌株特征进行报道,结合动物及食品源性菌株,表明我国stx2e亚型菌株具有高度遗传多样性,存在感染人的风险。

Objective To understand the molecular characteristics of Escherichia coli producing Shiga toxin 2e subtype isolated from different sources in China.Methods Three human-derived,13 animal-derived and eight food-derived stx2e-positive Escherichia coli strains which were isolated during 2012 to 2018 were analyzed by antimicrobial susceptibility testing and whole genome sequencing.The stx subtype,serotype,multi-locus sequence type,virulence genes and antimicrobial resistance genes of each strain were determined by whole genome sequences.The phylogenetic relationship and genetic composition of Shiga-toxin prophage were explored.Results Twenty-four stx2e-STEC strains were typed into 19 O∶H serotypes and 19 sequence types(STs).Each strain carried at least one kind of antimicrobial resistance gene and 19 out of 24 strains were resistant to at least one kind of antimicrobials.Three human-derived strains were heterogenous in serotypes and STs,but there were several animal and food-derived strains shared the same serotype or ST with human strains and showed close relationship in the phylogenetic analysis.The sequences of stx2e among all strains were highly conserved(similarity>99.7%),but there were significant differences in the size and the gene composition of Shiga toxin prophage genome.Conclusions This is report about the characteristics of rare human-derived Stx2e-STEC strains in China.Comparing human isolates with animal-and food-derived strains,it indicates that Stx2e-STEC strains are highly genetic diversity and have the potential to infect humans.