宋内志贺菌对氟喹诺酮类药物敏感性降低的相关耐药基因研究

Study on the resistance-related genes of Shigella sonnei with decreased susceptibility to fluoroquinolones

目的研究宋内志贺菌对氟喹诺酮类抗菌药物敏感性降低的相关耐药基因的变化情况。方法采用琼脂稀释法对131株宋内志贺菌进行药物敏感性检测，采用PCR法检测DNA旋转酶A亚单位（gyrA）、拓扑异构酶IVC亚单位（parC）基因的喹诺酮类药物耐药决定区（QRDR），并对PCR结果进行测序分析，同时用PCR法对质粒介导喹诺酮类耐药（PMQR）基因（qnr）和氨基糖苷乙酰转移酶变异基因[aac（6’）-Ib-cr]进行筛选。结果131株宋内志贺菌对萘啶酸的耐药率达100％，而对诺氟沙星、环丙沙星、左氧氟沙星全部敏感，对四环素、复方磺胺甲嚼唑和氨苄西林的耐药率分别为93．9％、92．8％和93．2％。94％的萘啶酸耐药宋内志贺菌株对氟喹诺酮类药物敏感性出现下降。萘啶酸耐药菌株gyrA均发生单点83位丝氨酸一亮氨酸（Ser→Leu）突变，但parC未发生突变；未检出qnr和nnc（6’）-Ib-cr基因。结论萘啶酸耐药宋内志贺菌对氟喹诺酮类药物敏感性降低，其产生的主要机制为gYrA发生83位Ser→Leu替换。

Objective To investigate the resistance-related genes of Shigella sonnei with decreased susceptibility to fluoroquinolones. Methods A total of 131 strains of Shigella sonnei were analyzed for their antimicrobial susceptibility. Mutations within the quinolone resistance determining regions （QRDR） of gyrA and parC were detected by polymerase chain reaction （PCR） and PCR products were then sequenced. Meanwhile, the plasmid-mediated quinolone resistance （PMQR）genes, qnr and aac（6＇）-Ib-cr were screened by PCR. Results Resistance rates of 131 Shigella sonnei isolates to nalidixic acid, tetracycline, ampicillin and trimethoprim-sulfamethoxazole were 100. 0%, 93.9%, 93.2 % and 92.8%, respectively. All strains were susceptible to norfloxaein, ciprofloxacin, levofloxacin, while 94% nalidixic acid-resistant Shigella sonnei strains showed reduced susceptibilities to fluoroquinolones. All of nalidixic acid-resistant Shigella sonnei strains presented a single mutation at codon 83 （Ser→Leu） of gyrA genes, but no mutations were detected in parC gene. And PMQR genes qnr and aac （6＇）-Ib-cr were not detected. Conclusions The nalidixic acid-resistant Shigella sonnei strains with reduced susceptibility to fluoroquinolones are common in the clinical practice, which may mainly due to a single mutation at codon 83 （Ser→Leu） of gyrA genes.