鸭源大肠杆菌对氟喹诺酮类耐药机制的研究

目的:分析鸭源大肠杆菌对喹诺酮类药物耐药机制。方法:微量肉汤稀释法测定4种喹诺酮类药物对22株鸭源大肠杆菌分离菌及恩诺沙星诱导耐药菌的抗菌活性,并通过PCR和DNA测序检测DNA促旋酶和拓扑异构酶Ⅳ基因(gyrA、gyrB、parC、parE)突变情况。结果:22株分离菌及诱导菌均扩增出目的片段,有18株菌对喹诺酮类药物耐药,耐药率约为82%。基因测序及分析表明:在9个测序菌株中,分别有5、2、6和7株出现gyrA、gyrB、parC和parE碱基突变;其中,gyrA基因突变,gyrB与parC或parE基因同时突变与耐药表型一致,3株仅有parC或parE基因突变的菌株并不明显耐药。gyrA基因突变均为双突变(Ser104→Leu和Asp108→Asn)。结论:鸭大肠杆菌对喹诺酮类药物的耐药严重,其主要机制是喹诺酮类耐药决定区(QRDR)的基因突变,特别是多个位点同时突变导致高水平耐药。

Study on Fluoroquinolones-tolerant Mechanism of Escherichia coli Isolated from Duck

In order to investigate the tolerant mechanism of Escherlchia coli isolated from duck to fluoroquinolones,the antibacterial activities of four species of fluoroquinolones medications against 22 strains of Escherichia coli from duck and the tolerant bacterium inducted by enrofloxacin were tested by using the broth microdilution method,and the mutation situations of DNA gyrAse and topoisomerase Ⅳ gene(gyrA,gyrB,parC,parE) were determined by using PCR and DNA sequencing method.The results indicated that the objective fragment was amplified from all 22 strains and the induced bacterium,18 strains of them had tolerance to fluoroquinolones,and the drug-tolerant rate was about 82%.The results of gene sequencing and analysis showed that the 5,2,6 and 7 strains of the tested 9 strains possessed gyrA,gyrB,parC and parE nucleotide mutations respectively.The mutation of gyrA,and the simultaneous mutation of gyrB and parC(or parE) were identical with the drug-tolerant phenotype.Three strains with only parC or parE mutation expressed insignificant drug tolerance.The gyrA mutation all was double mutation(Ser104→Leu and Asp108→Asn).It was concluded that the fluoroquinolones tolerance of Escherichia coli isolated from duck was obvious,and its main mechanism was the gene mutation of fluoroquinolones tolerance-deciding regions,especially the simultaneous mutations in multiple loci.