广州地区产CTX—M型超广谱β内酰胺酶大肠埃希菌和肺炎克雷伯菌的研究

Study on CTX-M type ESBLs-producing Escherichia coli and Klebsiella pneumoniae in Guangzhou

目的研究广州地区大肠埃希菌和肺炎克雷伯菌CTX-M型超广谱β内酰胺酶（ESBLs）的分子表型、流行病学和耐药基因环境特征。方法收集2007-2008年广州地区9家医院临床分离产ESBLs的181株大肠埃希菌和180株肺炎克雷伯菌，通过PCR检测ESBLs分子表型；通过接合试验、质粒图谱、PCR分析CTX-M-15型ESBLs的基因环境，肠杆菌科基因间重复序列引物PCR（ERIC—PCR）分析产CTX-M-15型ESBLs菌株的分子同源性。结果67．3％（243／361）的ESBLs产生株为CTX-M表型，其中CTX-M-1群和CTX．M-9群各占46．9％（114／243）和53．1％（129／243），未发现其他CTX-M亚群。CTX-M-14和CTXM-15是最常见的ESBLs基因型，其中CTX-M-14在大肠埃希菌和肺炎克雷伯菌的检出率分别35．4％（64／181）和28．3％（51／180），CTX-M-15在这两种菌的检出率分别为21．5％（39／181）和26．1％（47／180），此外还检出对头孢他啶有水解活性的CTX-M-55、CTX-M-19和CTX．M-27。采用ERIC—PCR分析CTX-M-15产生株的同源性，39株大肠埃希菌被分为28个基因型，47株肺炎克雷伯菌被分为30个基因型。67．6％（25／37）和32．4％（12／37）blaCTX-M-15分别位于65000bp和90000bp的可接合质粒上，65000bp质粒除blaCTX-M-15阳性外，未检到6laTEM-1、qnrB、blaDHA-1、blaOXA-1，aac（6′）-Ib-cr等耐药基因。1株接合菌90000bp质粒还存在b／aoxA-1和blaTEM-1耐药基因，其余7个90000bp质粒所携耐药基因同65000bp质粒。所有blaCTX-M-15都位于ISEep1-like插入序列下游，ISEepl-like末端与blaCTX-M-15间距均为48bp。结论广州地区ESBLs主要分子表型为CTX-M型主要流行为CTX-M-14型。以CTX-M-15为代表能水解头孢他啶的CTX-M型ESBLs在本地区检出增多值得关注。

Objective To study phylogenies, epidemiology and genetic environment of CTX-M type of ESBLs produced by Escherichia coli and KlebsieUa pneumoniae isolated from nine hospitals in Guangzhou. Methods The phylogenies of CTX-M type of ESBLs were analyzed by PCR. Genetic environment of CTX-M-15 encoding gene （ blaCTX-M-15 ） were investigated by conjugation test and plasmid analysis. The clonal relationship of strains producing CTX-M-15 was determined by enterobacterial repetitive intergenic consensus PCR （ERIC-PCR）. Results A total of 361 ESBLs-producing isolates of Escherichia coli and Klebsiella pneumoniae were collected. 67. 3% of ESBLs strains were detected to produce CTX-M-type ESBLs, and the commonest genotypes in Escherichia coli and Klebsiella pneumoniae were CTX-M-14 （35.4% and 28. 3% ）, CTX-M-15 （21.5% and 26. 1% ） ERIC-PCR products of all CTX-M-15-producing strains show 39 strains of Escherichia coli were classified into 27 genotypes while 43 strains of Klebsiella pneumoniae were divided into 30 genotypes. Furthermore, the genotypes of CTX-M-55, CTX-M-19, CTX-M- 27, with ceftazidime-hydrolyzing activity, were detected in this study. The great majority of blaCTX-X-15 genes were found to locate on a 65 000 bp-conjugative plasmid, and there was no blaTEM-1, b/aOXA-1, blaDHA-1 or aac （6＇）-Ib-cr gene coexisted on the plasmid. ISEcpl-like insertion sequences, relative to mobilization of b/aCTX-M-15 gene, were detected in all blaCTX-M-15 positive strains, and the distances between the end of ISEcpl- like insertion sequences and the start codon of blaCTX-M-15 were equal, with d8 base pairs. Conclusion CTX- M-14 is still the most common genotype of ESBLs in Guangzhou, but high prevalence of CTX-M-15 ESBLs hydrolyzing ceftazidime already appears in south China.