革兰阴性菌产CTX-M-3型超广谱β内酰胺酶分子传播机制的研究

Study on molecular transmission mechanisms of CTX-M-3 producing Gram-negative bacteria

目的 :了解革兰阴性菌产CTX M 3型超广谱β内酰胺酶 (ESBLs)的分子传播机制 ,为临床防治提供依据。 方法 :收集革兰阴性菌医院感染无重复株共 378株 ,进行药敏试验和ESBLs产酶株的检测 ;肠杆菌科基因组内重复一致序列 聚合酶链反应 (ERIC PCR)进行克隆株的DNA分型 ;质粒转移实验、质粒谱及耐药质粒酶切指纹分析、等电聚焦电泳、PCR扩增TEM、CTX M基因及其克隆测序进行ESBLs基因分型和质粒定位。结果 :ESBLs的检出率为 16 .9% (6 4 / 378) ,其中CTX M 3型产酶株占 2 0 .3% (13/ 6 4 ) ;CTX M 3基因定位在 6 6kb和 75kb 2种接合性质粒上 ,6 6kb的质粒同时携带TEM 1基因 ;从不同来源的CTX M 3产酶株中可以分离到同种耐药质粒 ,染色体DNA同源性分析显示其为不同的克隆株。结论 :CTX M 3型ESBLs产酶株的传播机制以质粒介导为主 ,并可能存在局部携带CTX M

Objective: To study the molecular transmission mechanisms of CTX M 3 ESBLs producing Gram negative bacteria for the control of its spreading. Methods: A total of 378 clinical isolates of Gram negative bacilli from three hospitals were collected, bacterial susceptibility testing and detection of ESBLs were done. ERIC PCR was carried out for DNA typing of clonal strains, plasmid transfer experiments, fingerprinting analysis, isoelectric focusing, and PCR for TEM, CTX M gene amplification and DNA sequencing was also carried out for ESBLs gene typing and plasmid location. Results: The incidence of ESBLs producing strains in Gram negative bacilli was 16.9%(64 /378), among them CTX M 3 producing strains account for 20.3% (13 /64). CTX M 3 gene was located on two types of transferable plasmids with size of 66 kb and 75 kb, the 66 kb plasmid also carried beta lactamases TEM 1 gene. Same resistant plasmid could be isolated from strains of different sources producing CTX M 3. Chromosomal DNA homologous analysis indicated that these strains being different clonal strains. Conclusions: The tranomission of CTX M 3 producing strains is mainly mediated by transferable plasmids, and local outbreak of resistant plasmids harbouring CTX M 3 gene possibly had occurred in these hospitals.