Frequency of Plasmid-mediated Quinolone Resistance Genes in Extended-spectum β-lactamase-producing Escherichia coli

Background and Plasmid-medicated quinolone resistance (PMQR) genes play an important role in resistance to quinolones. The aim of this study was to determine the frequency of PMQR genes in extended-spectrum β-lactamase-producing (ESBL) Escherichia coli.
This study was done on 240 isolates of E.­coli from urine samples of patients in Kermanshah, Iran. The susceptibility of isolates to selected antibiotics was tested using disc diffusion and broth microdilution methods. The isolates were screened for ESBL-producing phenotype by combined disc diffusion test. The qnrA, qnrB, qnrS, aac (6­')­-­Ib, and qepA genes were detected by PCR. All PCR products for aac­(6')­-Ib gene were digested by BtsCI for detection of aac­(6')­-Ib-cr variant. Data analysis was done using statistical methods.
Of 66 ESBL-producing isolates, 45 (68.1%) were resistant to ciprofloxacin and levofloxacin and 56 (84.8%) were found to be resistant to nalidixic acid. The qnrA, qnrB, qnrS, and qepA genes were detected in 28.7%, 40.9%, 4.5%, and 3% of the isolates, respectively. The aac­(6')­-Ib gene was found in 65.1% of the isolates amongst which 88.4% were aac­(6')­-Ib-cr variant.
Our results indicate a high prevalence of PMQR genes in ESBL-producing E.coli isolates in Kermanshah. A correlation was observed between resistance to beta-lactams and quinolones which may indicate the cotransfer of quinolone genes by plasmids carrying the ESBL. As a result, identifying E. coli strains with ESBL may indicate a high resistance to quinolones. So, before using quinolones, the screening test for ESBL is recommended to prevent the increasing resistance to this class of drugs.