猪源大肠杆菌质粒和染色体介导的喹诺酮类药的耐药机制

Mechanism of plasmid-and chromosome-mediated quinolone resistance in Escherichia coli isolated from pigs

采用微量肉汤稀释法对31株猪源大肠杆菌进行6种喹诺酮类药物的敏感性测定,聚合酶链式反应检测质粒介导的喹诺酮类耐药(PMQR)基因qnr、qepA和aac(6′)-Ib-cr,并分析PMQR基因阳性菌株染色体gyrA、gyrB、parC、parE基因的喹诺酮耐药决定突变区(QRDRs)突变。结果显示,31株猪源大肠杆菌对兽医临床常用的氟喹诺酮类药物均呈现耐药。在31株猪源肠杆菌中共检测到2株携带qnrB10和4株携带qnrS1基因的大肠杆菌,未检测到qnrA、qepA和aac(6′)-Ib-cr。在PMQR阳性菌株gyrA基因的QRDRs中,低耐药菌株的gyrA基因出现83位S→W突变,高耐药菌株的gyrA基因同时出现83位S→L和87位D→N突变。而在parC基因的QRDRs中,大部分耐药菌株出现80位S→I突变,1株耐药菌株出现45位V→L突变。gyrB和parE基因的QRDRs未检测到突变。结果表明,本地区猪源大肠杆菌对兽医临床常用的氟喹诺酮类药物耐药严重,PMQR的出现和QRDRs的点突变可同时协同贡献对喹诺酮类耐药,而PMQR的出现加速了喹诺酮类耐药基因的快速传播。

Susceptibility of 31 Escherichia coli strains isolated from pigs to six quinolones was determined by microdilution method.The plasmid-mediated quinolone resistant（PMQR） determinants qnr,qepA and aac（6′）-Ib-cr were screened by PCR.Mutations in the quinolone-resistance-determining region（QRDRs） of the gyrA,gyrB,parC and parE gene were analyzed in PMQR positive strains.The results indicated that all isolates displayed resistance to quinolones.Among these isolates,two isolates were detected qnrB10 positive and four isolates qnrS1 positive,no qnrA,qepA or aac（6′）-Ib-cr were detected.In the low level resistant isolate,the mutation of S→W in 83 site of the gyrA QRDRs was observed,while in the high-level resistant isolates,the mutation both S→L in 83 site and D→N in 87 site in the QRDRs of the gyrA were observed.For most isolates,the mutation of S→I in 80 site of parC QRDRs were also found,except one isolate,V→L in 45 site of parC QRDRs occurred.No mutations were detected in QRDRs of gyrB and parE.These data suggested that Escherichia coli isolated from pigs in this region exhibited serious quinolone resistace.PMQR together with mutations in QRDRs conferred the quinolone resistance.The emergence of PMQR will accelerate the rapid dissemination of quinolone resistance genes.