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) →TTG(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.