产NDM-1肠杆菌科细菌的耐药机制和临床特征

Mechanism of drug resistance of NDM-1 producing Enterobacteriaceae and the clinical feature of its infection

目的 探讨临床分离的产NDM-1肠杆菌科细菌的耐药机制及携带blaNDM-1质粒的特征和基因环境.方法 连续收集2011年8月至2013年1月华南地区6家综合性医院临床非重复分离的碳青霉烯类耐药肠杆菌科细菌48株,同时选择大肠埃希菌J53作为接合试验受体菌.对所有菌株进行碳青霉烯水解酶表型试验（改良Hodge试验）,用PCR法检测碳青霉烯类水解酶相关基因.通过脉冲场凝胶电泳（PFGE）观察携带blaNDM-1质粒的大小,通过对质粒进行酶切分析质粒的同源性及不相容群分型,并对临床上产NDM-1细菌感染患者的临床特征进行分析.结果 48株耐碳青霉烯类肠杆菌科细菌中有43株改良Hodge试验阳性.碳青霉烯酶耐药基因检测结果示,48株肠杆菌科细菌bla VIM、blaGIM和blaSPM均为阴性,19株细菌blaNDM-1基因为阳性,分别为3株大肠埃希菌、5株肺炎克雷伯菌、6株阴沟肠杆菌、3株弗劳地柠檬酸杆菌、1株产酸克雷伯菌和1株雷氏普罗威登斯菌.药敏试验结果显示,19株细菌均对亚胺培南、头孢噻肟、头孢他啶、头孢吡肟、氨曲南和哌拉西林/他唑巴坦耐药,对环丙沙星和左氧氟沙星的耐药率均为47.3％,但对阿米卡星的敏感率为68.4％.有13株产blaNDM-1细菌携带的blaNDM-1质粒均成功转移到大肠埃希菌J53中.接合子药敏试验结果显示,对亚胺培南、头孢他啶、头孢噻肟和哌拉西林/他唑巴坦仍耐药,但对阿米卡星、环丙沙星和左氧氟沙星均敏感.基因环境结果显示,接合子J-FR90（雷氏普罗威登斯菌）所有基因为阴性,其余12株细菌携blaNDM-1质粒blaSHV、aac-（6＇）-Ib基因均为阳性.PFGE显示,携blaNDM-1质粒大小基本一致,为50 kb左右.质粒之间有相似的酶切图谱,其相似度＞80％.质粒不相容群为IncX3型.菌株传代500代后,PCR检测显示所携带的blaNDM-1质粒均未丢失.19例产NDM-1细菌感染患者中6例死亡,13例存活.结论 华南地区已出现产NDM-1的肠杆菌科细菌,主要通过IncX3型质粒在肠杆菌中传播.感染此类细菌的患者预后良好.

Objeetive To explore the mechanism of drug resistance of New Delhi metallo-β-lactamase-1 （NDM-1） producing Enterobacteriaceae,and to investigate the characteristics of blaNDM-1 carrying plasmid and its gene environment.Methods A total of 48 strains of carbapenem-resistant Enterobacteriaceae were successively collected from six general hospitals in south China during August 2011 and January 2013.Escherichia coli J53 was used for plasmid conjugation.Modified Hodge test was performed,and PCR method was used for the detection of carbarpenase-related genes.The relative molecular mass of the blaNDM-1 carrying plasmid was determined using pulsed field gel electrophoresis （PFGE）assay,and enzyme digestion was performed to investigate the homology and incompatibility group of the plasmid.Clinical feature of blaNDM-1 producing Enterobacteriaceae infection was also investigated.Results Among 48 strains of carbapenem-resistant Enterobacteriaceae,43 were positive in modified Hodge tests.blaVIM,blaGIM and blaSPM genes were negative in all strains,while blaNDM-1 was positive in 19 strains including 3 strains of Escherichia coli,5 strains of Klebsiella pneumoniae,6 strains of Enterobacter cloacae,3 strains of Citrobacterfreundii,1 strain of Klebsiella oxytoca and 1 strain of Providencia rettgeri.All the 19 strains were resistant to imipenem,cefotaxime,ceftazidime,cefepime,aztreonam and piperacillin/tazobactam,47.3％ strains were resistant to ciprofloxacin and levofloxacin,but 68.4％ strains were sensitive to amikacin.Conjugation experiment showed that,blaNDM-1 carrying plasmids in 13 strains were transmitted to the Escherichia coli J53.The conjugants were resistant to imipenem,ceftazidime,cefotaxime and piperacillin/tazobactam,but were sensitive to amikacin,ciprofloxacin and levofloxacin.All genes in conjugant J-FR90 （Providencia rettgeri） were negative,while the remaining 12 conjugants carried blaNDM-1,blaSHV and aac-（6＇）-Ib genes.PFGE showed that,the sizes of all blaNDM-1 carrying plasmids were about 50 kb,and more than 80％ of their macrorestriction maps were similar.The plasmid belonged to incompatibility group IncX3,and exhibited 100％ passage stability after 500 generations of propagation.Among 19 patients infected with NDM-1 producing Enterobacteriaceae,6 died and 13 survived.Conclusions NDM-1 producing Enterobacteriaceae is emerging in south China,and blaNDM-1 is transmitted to Enterobacteriaceae through IncX3.Patients infected with NDM-1 producing Enterobacteriaceae usually have good prognosis.