ST131型产NDM-1型碳青霉烯酶大肠埃希菌的耐药机制研究

Investigation on drug resistance mechanism of NDM-1-producing ST131 Escherichia coli strain

目的探讨我院首株临床分离的产NDM-1型碳青霉烯酶大肠埃希菌耐药特征及其传播机制。方法用Vitek 2Compact全自动微生物分析系统进行菌株鉴定及耐药初筛;微量肉汤稀释法和E-test试纸条检测药物最低抑菌浓度(MIC);改良Hodge试验、亚胺培南-EDTA协同试验检测金属β-内酰胺酶;PCR以及测序方法检测大肠埃希菌耐药基因;多位点序列分型(MLST)技术进行序列分型;S1-PFGE、Southern印迹杂交和质粒不相容性分型方法研究携带bla_(NDM-1)质粒的特征。结果该菌对包括亚胺培南、美罗培南和厄他培南在内的β-内酰胺类抗菌药物、左氧氟沙星、庆大霉素均耐药,对阿米卡星、替加环素以及多黏菌素B敏感。改良Hodge试验、亚胺培南-EDTA协同试验阳性;PCR扩增产物测序结果经BLAST比对后显示携带bla_(NDM-1)、bla_(CTX-M-14)和qnr S基因;MLST序列分型为ST131型;bla_(NDM-1)位于大小约为100 000 bp的IncN型质粒上,且该质粒可通过接合传播。结论新出现的产NDM-1型碳青霉烯酶大肠埃希菌为ST131型,bla_(NDM-1)基因可通过质粒传播,临床应加强监测以防止耐药菌传播。

Objective To investigate the drug-resistant features and transmission mechanism of a strain of New Delhi metalloproteinase-1 （ NDM-1 ）-producing Escherichia coli （E. coli） first isolated in our hospital. Methods Bacterial identification and in vitro antimicrobial susceptibility tests were initially determined by Vitek-2 Compact system, followed by broth mierodilution method and E-test to measure the minimum inhibitory concentrations （MICs） for several antibiotics. The modified Hodge test and imipenem-EDTA synergy test were used to screen the production of metallo-13-1actamase. PCR and nueleotide sequencing methods were performed to detect drug resistant genes of Escherichia coli. The type of sequence was determined by multilocus sequence typing （MLST） method. S1- pulsed field gel electrophoresis （PFGE） , Southern blotting and PCR-based replicon typing method were conducted to analyze the characteristics of the plasmid which carried blaNDM-1. Results This E. coli strain showed resistant to all 13-1actams antibiotics （ including imipenem, meropenem and ertapenem）, levofloxacin and gentamicin, but susceptible to amikacin, tigeeyclin and polymyxin B. The modified Hodge test and imipenem-EDTA synergy test were both positive. Nueleotide sequences of positive amplification were analyzed using BLAST and revealed that the strain carried blaNDM-1 , blaCTX-M-14 and qnrS gene. The sequence typing of MLST suggested this strain was ST131. blaNDM-1 was located in a transferrable IneN plasmid with a size of about 100 000 bp. Conclusion The newly emerged E. coli strain was identified as NDM-l-producing ST131 type, and the carried blaNDM-1 gene could be transmitted through plasmid. Strict surveillance should be necessary to avoid further clinical dissemination of this drug-resistant E. coli strain.