志贺菌gyrA、parC基因突变与喹诺酮类耐药

目的探讨DNA旋转酶A亚单位（gyrA）和拓扑异构酶Ⅳ C亚单位（parC）基因突变与志贺菌耐喹诺酮类药物的相关性。方法用聚合酶链反应（PCR）检测志贺菌喹诺酮耐药决定区（QRDR）相关gyrA、parC基因并挑选11株菌扩增片段进行DNA测序，分析突变位点与药敏结果的关系。结果11株扩增片段测序结果显示，9株耐萘啶酸菌均在gyrA83位发生有意义突变TCG（Ser）→TTG（Leu），宋内志贺菌未发生parC基因突变，5株耐萘啶酸、诺氟沙星和／或环丙沙星中介敏感福氏志贺菌在parC80位发生有意义突变AGC（Ser）→ATc（Ile）。结论志贺菌对喹诺酮类药物耐药严重，福氏志贺菌比宋内志贺菌更耐此类药物，靶酶基因突变是其耐喹诺酮类药物的主要机制之一，gyrA Ser83→Leu突变是导致志贺菌临床株对萘啶酸耐药的关键突变。parC基因突变在gyrA基因突变的基础上才会发生，parC突变可能引起诺氟沙星和／或环丙沙星不敏感。

Relationship between the quinolone resistance and mutations in the gyrA and parC genes in Shigella

Objective To identify the mutations of DNA gyrase gyrA and topoisomerase IV parC genes in quinolone-resistant Shigella clinical isolates and evaluate the relevance of variations in gyrA and parC to quinolone resistance. Methods GyrA and parC genes belonging to QRDR were detected by polymerase chain reaction （PCR）. In order to investigate the correlations between quinolone resistance and changes in gyrA and parC, 11 Shigella clinical isolates were selected for sequencing. Results DNA sequence of 11 isolates revealed that sense mutations in gyrA and parC were commonly observed in quinolone-resistant isolates. The most frequent mutation was at codon 83 TCG （Ser） →TrG （Leu） of gyrA in 9 quinolone-resistant strains. All Shigella sonnei isolates were not found sense mutations of parC. 5 isolates of Shigella flexneri with nalidixic acid resistance, norfloxacin and/or ciprofloxacin intermediate had been found the sense mutation at codon 80 AGC （Ser） →ATC （Ile） of parC. Conclusions The Shigella spp has a comparative high resistance to quinolone resistance. Shigella flexneri was more resistant than Shigella sonnei. The target gene mutations are the main mechanism of quinolone resistance. The substitution Leu to Ser83 in gyrA is the pivotal mutation that resulting in nalidixic acid resistance in Shigella clinical isolates. Norfloxacin and/or ciprofloxacin is non-susceptible probably causes by parC mutation which happened after gyrA＇s.