志贺菌临床株耐药性分析及对氟喹诺酮类抗生素耐药机制的研究

Analysis of Antimicrobial-Susceptibility and Fluoroquinolone-Resistance in Clinical Isolates of Shigella

目的:了解本地区志贺菌抗生素耐药情况,探讨志贺菌对氟喹诺酮类药物的耐药机制和耐药基因的突变及流行情况。方法:K-B纸片扩散法测定2009—2010年天津地区临床分离的119株志贺菌的药敏情况,对氟喹诺酮耐药志贺菌的gyrA、parC基因及质粒介导的喹诺酮耐药(PMQR)基因qnrA、qnrB、qnrS、aac(6′)-ib-cr、qepA进行扩增、测序,将PMQR阳性菌株与大肠埃希菌J53ARZ进行质粒接合试验,比较接合前后受体菌对抗菌药物的敏感性变化。结果:119株志贺菌对萘啶酸敏感率最低(1.72%),其次为氨苄西林(2.52%)及复方磺胺甲口恶唑(3.36%)。福氏志贺菌与宋内氏志贺菌对氟喹诺酮耐药性差别较大,5株志贺菌对环丙沙星等氟喹诺酮耐药,均为福氏志贺菌,其中2株对左氧氟沙星耐药。4株同时存在gyrA83、87位点及parC80位点突变,1株缺乏gyrA87位点突变。PMQR基因阳性菌3株,包括1株qnrS及2株aac(6′)-ib-cr阳性菌,接合菌对多种抗生素的敏感性降低。结论:本地区志贺菌临床株对多种抗生素的多重耐药率较高,对氟喹诺酮耐药率低于5%。喹诺酮耐药机制既有染色体介导靶位酶突变,也存在质粒介导喹诺酮耐药。

Objectives：To investigate the antimicrobial resistance characteristics of shigella in Tianjin,and the mechanism of fluoroquinolone-resistance thereof.Methods：A total of 119 clinical isolates of shigella identified in Tianjin from 2009 to 2010 were analysed by K-B disk diffusion method for their antimicrobial susceptibility.The gyrA and parC in fluoroquinolone-resistant stains and plasmid mediated quinolone resistant （PMQR） determinants （qnrA,qnrB,qnrS,aac（6′）-ib-cr and qepA） were amplified and sequenced.Conjugation test was performed for PMQR determinant positive strains.The antimicrobial-susceptibility of E.coli J53AZR was compared before and after conjugation test.Results：The susceptibility rate of 119 shigella strains to nalidixic acid was the lowest （1.72%）,followed was ampicillin （2.52%） and sulfamethoxazole （3.36%）.There were significant differences in sensitive rates to fluoroquinolone between shigella sonnei and shigella flexneri.Five isolates of Shigella flexneri were resistant to fluoroquinolone,in which 2 isolates were resistant to ciprofloxacin,2 isolates were resistant to levofloxacin and 4 to double mutations （gyrA83,87 and parC80）.There were 3 PMQR positive strains,including 1 strain qnrS,2 strains of aac（6′）-ib-cr.E.coli J53AZR,showed decreased susceptibility to many antimicrobial after conjugation.Conclusion：Shigella clinical isolates showed high resistance rate to many antibiotic,but low resistance rate to fluoroquinolone （5%）.The mechanisms of fluoroquinolone resistance in shigella included both sense mutations at target enzyme in quinolone-resistance determining regions and harboring plasmid mediate quinolone-resistance gene.