大肠埃希菌染色体、质粒介导的喹诺酮类药物耐药机制研究

Mechanisms Of chromosome-and plasmid-mediated quinolones resistance in Escherichia coli strains isolated from ICU

目的探讨我院ICU病区临床分离大肠埃希菌(Escherichia Coli. ECO)的耐喹诺酮类抗菌素耐药机制。方法收集2007年12月～2008年6月期间20株分离自我院ICU病区患者临床标本的ECO菌,采用纸片扩散法测定30种抗菌药物的敏感性,微量琼脂稀释法测定环丙沙星、左氧沙星的MIC值;采用PCR法联合检测细菌染色体介导DNA解旋酶gyrA和质粒介导的qnrA、qnrB、qnrS以及aac(6’)-Ⅰb-Cr变异体和与喹诺酮类外排有关的qepA等6种基因。结果20株ECO菌gyrA基因均存在突变,其中13、15号株gyrA基因经比对与美国NCBI中已登录的gyrA基因序列均不相同,为新亚型;检出aac(6’)-Ⅰb基因3株,经比对分别为aac(6’)-Ⅰb(2株)和aac(6’)-Ⅰb-Cr(1株);qnrA基因检出1株,经比对为qnrA1。结论本组ECO菌对环丙沙星等喹诺酮类耐药主要为gyrA基因突变所致,但也有aac(6’)-Ⅰb-Cr、qnrA1的因素。

Objective To study on the mechanisms of chromosome-and plasmid-mediated quinolones resistance in Escherichia coli.Methods Twenty E.Coli clinical isolates were collected from clinical specimens at ICU of Yinzhou People’s Hospital from Dec.2007 to June 2008. To detect the susceptibility to 30 types of antibiotics,K-B disk diffusion method was used. Those of ciprofloxacin and levofloxacin were detected by agar dilution testing.Then six type genes gyrA,qnrA,qnrB,qnrS,aac(6’)-Ib-cr,qepA were investigated by PCR. In the meantime,the PCR products were sequenced. Results The alterations in gyrA were found in all tested strains. Two new subtypes were found in Eco13 and Eco15. acc(6’) -Ib-cr was found in three strains and qurA was detected in Eco2.Conclusion The mutations in gyrA would play a dominant role in the resistance to quinolones in E.Coli. Both aac(6’)-Ib-cr and qepA may responsible for quinolones resistance in E.Coli too.