志贺菌质粒介导喹诺酮类耐药基因研究

Study on genotypes of plasmid-mediated quinolone in Shigella

目的了解志贺菌中质粒介导喹诺酮类耐药基因qnrA、qnrB、qnrS和aac（6’）．Ib-cr的流行情况以及其耐药特征。方法PCR法对57株志贺菌进行qnrA、qnrB、qnrS和aac（6’）-Ib基因检测，PCR扩增阳性菌株进行测序和基因分型，并与大肠埃希菌J53作接合试验，采用琼脂稀释法检测志贺菌和接合前后大肠埃希菌J53对抗菌药物的最小抑菌浓度（MIC）；特异性PCR扩增确认接合子基因型。结果57株志贺菌中，筛选出qnrS、qnrB阳性株各1株（ZH13和ZH53），均为福氏志贺菌，其基因序列在NCBI成功登录，登录号分别为FJ616991和FJ616990，未检出qnrA和aac（6’）-Ib基因；其中ZH13接合试验成功，ZH53不能接合，接合试验后的大肠埃希菌J53对多种抗菌药物的MIC明显提高；特异性PCR证实接合子和供体菌有相同的qnr基因。结论在志贺菌中检出qnrS基因，且国内首次检出qnrB基因，qnr阳性菌株呈多重耐药，且其耐药性可以通过接合方式发生水平转移，需加强监控。

Objective To investigate the prevalence of qnrA, qnrB, qnrS and aac （6＇）- I b-cr genes in Shigella isolates and their characterization of resistance. Methods qnrA, qnrB, qnrS and aac （6＇）- I b genes in 57 isolates of Shigella were detected by PCR, DNA sequencing and genotyping were per- formed. PCR positive strains, conjugation test was performed and E. coli J53 as receptor. Minimum inhibi- tory concentration（MIC） of ShigeUa and E. coli J53 before and after conjugation test were determined by agar dilution method. PCR were used to determine the genotype of eonjugon. Results The qnrS and qnrB genes were identified in two isolates（ ZH13 and ZH53 ） , and all were Shigellaflexneri. The sequence acces- sion number in NCBI database are FJ616991, FJ616990 separately, qnrA and aac（6＇）- I b-cr genes were not found in all isolates. ZH13 conjugation were successful, and ZH53 repetitive conjugation were unsuc- cessful, the MIC of E. coli J53 were increased evidently after conjugation. The qnr genotype of conjugon was similar to donator. Conclusion We identified qnrS gene in Shigella flexneri strains, and identified qnrB gene in Shigellaflexneri in China for the first time. The qnr gene positive strains were multiplex resistant and the resistance of these strains could be transfered, so it should be monitored carefully.