大肠埃希菌临床分离株对喹诺酮类抗菌药的质粒介导耐药

Plasmid-mediated quinolone resistance in clinical isolates of Escherichia coli

目的了解近年来发现的质粒介导耐药机制在大肠埃希菌临床株对喹诺酮类耐药中所起的作用。方法78株环丙沙星耐药菌株分离自上海5所教学医院。以克隆斑点杂交及Southern杂交方法筛选质粒介导耐药基因qnr；以接合试验了解喹诺酮耐药的可转移性；对qnr基因进行序列分析,以引物步移法对qnr周边质粒DNA进行测序、分析。结果78株大肠埃希菌中,6株(7．7%)qnr检测阳性。在6株阳性菌中,喹诺酮耐药性均可通过质粒转移,接合子对环丙沙星的MIC较受体菌上升16～250倍。qnr基因与最早报道的序列一致,qnr位于In4族的Ⅰ类整合子上,本研究中的2个新整合子命名为In36及In37。结论与qnr相关的质粒介导喹诺酮类耐药性在大肠埃希菌临床分离株中有一定程度流行,这可能是我国细菌对喹诺酮类耐药性上升迅速的原因之一。

Objective To investigate the importance of recently discovered plasmid-mediated quinolone resistance in the development of quinolone resistance in clinical isolates of Escherichia coll. Methods Seventy-eight unique ciprofloxacin-resistant clinicalisolates of E. coli from 5 Shanghai hospitals were screened for the qnr gene by colony blotting and Southern hybridization of plasmid DNA. Conjugation experiments were done with azide-resistant E. coli J53 as a recipient, with selection for plasmid-encoded antimicrobial resistance （chloramphenicol, gentamicin, or tetracycline）, and azide counterselection, qnr genes were sequenced, and the structure of plasmid DNA adjacent to qnr was analyzed by primer walking. Results qnr was detected in six（7.7%） of 78 strains. Quinolone resistance was translerred Iroln all the six probe-positive strains ,Transconjugants had 16-to 250-fold increases in M1Cs of ciprofloxacin relative co that of the recipient. All six strains contained qnr with a nucleotide se quence identical to that originally reported, qnr was located in complex In4 family class 1 integrons. Conclusions Transferable plasmid-mediated quinolone resis＇rance associated with qnr existed in quinolone-resistant E. coli strains in Shanghai hospitals and may contribute to the rapid increase of bacterial resistance to quinolones in China.