产超广谱β内酰胺酶大肠埃希菌及肺炎克雷伯菌磷霉素耐药机制研究

Mechanisms of fosfomycin resistance of extended-spectrum β-lactamases-producing Escherichia coli and Klebsiella pneumoniae

目的观察磷霉素对产超广谱β内酰胺酶（ESBLs）大肠埃希菌及肺炎克雷伯菌的体外抗菌活性，并探究其耐药机制。方法收集来自全国22个省市28家医院血流感染来源的产ESBLs大肠埃希菌及肺炎克雷伯菌1 052株，根据美国临床和实验室标准协会（CLSI）（2015版）标准，采用琼脂稀释法测定磷霉素对1 052株临床分离菌株的最低抑菌浓度（MICs）；PCR法及测序筛选磷霉素耐药相关的基因。结果磷霉素对产ESBLs大肠埃希菌和肺炎克雷伯菌的敏感率分别为91.3%（818/896）和91.7%（143/156）；共发现91株磷霉素不敏感菌株，其中73株（80.2%）携带fosA3基因；其余18株fosA3基因阴性的菌株中，16株有染色体相关基因的突变或插入失活，2株未发现任何耐药基因。结论磷霉素对产ESBLs大肠埃希菌和肺炎克雷伯菌均具有良好的体外抗菌活性，而fosA3基因是导致我国大肠埃希菌和肺炎克雷伯菌对磷霉素不敏感的主要机制，染色体介导的磷霉素耐药机制也可能起着一定的作用。

ObjectiveTo study the in vitro activity of fosfomycin to extended-spectrum β-lactamases （ESBLs）-producing Escherichia coli and Klebsiella pneumoniae and to explore the mechanisms of fosfomycin resistance.MethodsA total of 1 052 ESBLs-producing E. coli（ESBL-EC） and K. pneumoniae（ESBL-KP） isolates were collected from bloodstream infections of 28 hospitals of 22 provinces and municipalities, which were stored by our laboratory.Minimum inhibitory concentrations （MICs） of fosfomycin against these clinical isolates were determined by agar dilution methods according to the Clinical and Laboratory Standards Institute （CLSI）（2015）. The genes related to fosfomycin resistance were confirmed by Polymerase Chain Reaction （PCR） and sequencing.ResultsThe susceptibility rates of ESBL-EC and ESBL-KP isolates to fosfomycin were 91.3% （818/896） and 91.7% （143/156）, respectively. A total of 91 fosfomycin-non-susceptible isolates were detected, of which 73 （80.2%） isolates carried fosA3 genes.Amongst 18 fosA3-negative isolates, 16 isolates were detected to have chromosomal mutations or insertion inactivation, while the rest two isolates had not been detected any resistant mechanisms.ConclusionsFosfomycin shows great in vitro antimicrobial activity to ESBL-EC and ESBL-KP. The primary mechanism of fosfomycin-non-susceptible isolates is fosA3 gene.Chromosomal mutations may also involve in the fosfomycin resistance.