Study on the resistance-related genes of Shigella sonnei with decreased susceptibility to fluoroquinolones / 中华传染病杂志

ABSTRACT

Objective To investigate the resistance-related genes of Shigella sonnei with decreased susceptibility to fluoroquinolones.MethodsA 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.ResultsResistance 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 norfloxacin,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.