Genes conferring quinolone resistance in Shigella flexneri / 中国感染与化疗杂志

ABSTRACT

Objective To investigate the antimicrobial resistance proifle of Shigella flexneri in Shanghai from 2010 to 2014 and examine the mechanism of fluoroquinolone resistance.Methods Kirby-Bauer method was used to determine the susceptibility of the S. flexneri strains to 14 antibiotics. The minimum inhibitory concentration (MIC) of ciprofloxacin was tested by E-test. Mutations within quinolone resistance determining regions (QRDR) of gyrA and parC and plasmid-mediated quinolone resistance (PMQR) genes,qnrA,qnrB,qnrS andaac(6')-Ib-crwere identified by polymerase chain reaction (PCR). All the products were subjected to sequencing analysis.Results More than 90 % of the 139S. flexneri isolates were resistant to ampicillin, streptomycin, tetracycline, and nalidixic acid, 40.3 % to ciprofloxacin and 30.2 % to cefepime, respectively. Genetic mutation of gyrA and parC was found in 98.6 % and 97.8 % of the strains, respectively. Three point mutations (Ser83, Asp87 and His211) were detected in gene gyrA and one point mutation (Ser80) was found in in gene parC. Plasmid-mediated resistant gene qnrS was found in 9 strains and aac(6')-Ib-cr in 6 strains.Conclusions The antibiotic resistance of S. flexneri is serious in Shanghai. The mutation rate within QRDR is high. Point mutation in Asp87 of gyrA is the main mechanism of quinolone resistance. The plasmid-mediated quinolone-resistant genes also play an important supplementary role.