耐环丙沙星患病动物源沙门菌的多重耐药分子特征

Molecular characterization of ciprofloxacin-resistant Salmonella isolates from sick animals

采用13株耐环丙沙星食品动物源沙门菌进行喹诺酮类作用靶位基因及质粒介导耐药基因的扩增测序、有机溶剂耐受试验、HeLa细胞侵袭试验,探讨其多重耐药的分子特征。结果显示,菌株均携带质粒介导的喹诺酮耐药基因,7株对环丙沙星敏感性降低或低水平耐药(最小抑菌浓度0.125～4μg/mL),靶位基因无突变或gyrA单位点突变及外排泵活性增强;5株对环丙沙星高水平耐药(最小抑菌浓度32～128μg/mL),均在gyrA和parC发生双位点突变及外排泵活性增强,其中4株携带β内酰胺酶blaCTX-M基因。对环丙沙星高水平耐药的沙门菌的侵袭力显著高于敏感菌株。表明患病食品动物源沙门菌中,无论外排能力增强与否,gyrA单位点突变或质粒介导的喹诺酮耐药基因阳性,仅导致沙门菌对环丙沙星的低水平耐药;而外排泵机制联同染色体靶位基因突变可导致菌株对环丙沙星的高水平耐药,往往同时携带blaCTX-M基因;临床分离沙门菌随着对环丙沙星耐药程度的增加侵袭力增强。

A total of 13 non-duplicate Salmonella isolates resistant to ciprofloxacin were collected from sick food-producing animals subjected to phenotypic characterization including the amplification of plasmid- mediated quinolone resistance（PMQR） genes,as well as fl-lactamases encoding genes only in PMQR posi- tive isolates by PCR, the screening of mutations in the quinolone resistance-determining regions of gyrA and parC by PCR. The qnr,aac（6′）-Ib-cr and oqxA genes were detected in 13 of the isolates and were fre- quently co-prevalent. Seven isolates demonstrated reducing susceptible or low resistant for ciprofloxacin with minimal inhibitory concentration（MIC） from 0. 125 to 4μg/mL. These isolates had either single muta- tion in gyrA or no mutation in any target genes as well the active efflux. Five isolates except one presented double mutations in both gyrA and parC and the active efflux conferring high resistant level to ciprofloxa- cin（MIC,32--128μg/mL）. Only blacTx-M type ESBLs were detected in 4 isolates with PMQR presenting high level of resistance to ciprofloxacin. Reduced ciprofloxacin susceptibility was arisen from either single mutation in gyrA or the presence of PMQR genes,irrelevant to the active efflux,while high level of resis- tance to ciprofloxacin was conferred by chromosomal mutations in target genes combining with active efflux.