临床与环境标本分离的大肠埃希菌bla_(CTX-M-14)基因环境和菌株同源性分析

Analysis of the genetic environment and homology of bla_(CTX-M-14)in Escherichia coli isolates from clinical and environmental samples

目的分析临床与环境标本分离的大肠埃希菌blaCTX-M-14基因环境和菌株同源性。方法收集2014年6月至2014年8月我院临床与环境标本分离的大肠埃希菌共255株,PhoenixTM-100鉴定细菌种类并测定最小抑菌浓度,纸片扩散法测定超广谱β-内酰胺酶表型,PCR扩增blaCTX-M-14基因;接合实验、质粒复制子分型分析质粒特征;脉冲场凝胶电泳和多位点序列分型对菌株分型。结果 blaCTX-M-14基因的阳性共26株。多数菌株(42.3%,11/26)含有F型质粒,且多具有可转移性。多位点序列分型多为ST131(30.8%,8/26)。仅有4株菌能在环境或大便标本中找到同源株。多数菌株(61.5%,16/26)blaCTX-M-14基因环境均具有相同的模式:上游有ISEcp1,同时下游有IS903。结论 blaCTX-M-14基因可通过医院环境或体内移位获得,但其广泛传播的原因可能与其编码在F型质粒上及其基因环境中存在ISEcp1和IS903有关。

Objective To analyze the genetic environment and homology of blaCTX-M-14 in Escherichia coli isolates from clinical and envi- ronmental samples. Methods A total of 225 Escherichia coli isolates were collected from clinical and environmental samples during June 2014 and August 2014. The identification and minimum inhibitory concentration （MICs） of these isolates were determined by PhoenixTM-100. The determinations of extended spectrum β-1actamase （ESBL） and blaCTX-M-14 gene were performed by disk diffusion method and PCR, respectively. The plasmid characterization was analyzed by conjugation test and PCR-based replicon typing （PBRT）, and the molecular typing of the isolates by pulsed-field gel electrophoresis （PFGE） and muhilocus sequence typing （MLST）. Results Among the 26 isolates with positive blaCTX-M-14, 11 （42.3 % , 11/26） had transferable IncF plasmid, and 8 （30. 8%, 8/26） belonged to ST131 type. Although four homology isolates were found in environmental and feces samples, most isolates （61.5% , 16/26） had the same genetic environment, that is, ISEcpl element was identified in the upstream region of the blaCTX-M-14 gene and IS903 element in the downstream region. Conclusion The blaCTX-M-14 gene may be acquired from environmental or feces sam- pies, which may be related to transferable IncF plasmid and the existence of ISEcpl and IS903 elements in blaCTX-M-14 gene.