Molecular characteristics of qnrS1-positive Escherichia coli resistant to quinolone

Abstract

Objective To analyze the molecular characteristics of qnrS-positive Escherichia coli (E.coli) strains resistant to quinolone. Methods A total of 57 qnrS1-positive clinical isolates were collected from Fujian Medical University Union Hospital. Plasmid-mediated quinolone resistance (PMQR) genes [qnrA, qnrB, qnrC, qnrD, aac(6′)-Ib-cr, qepA and oqxAB] and β-lactamase genes (blaCTX-M-1, blaCTX-M-2, blaCTX-M-8, blaCTX-M-9, blaSHV and blaTEM) were detected by PCR and then sequenced. Agar dilution method was used to analyze the antimicrobial susceptibility of the qnrS1-positive strains. Phylogenetic analysis was conducted using PCR. Multilocus sequence typing (MLST) was performed for phenotyping. Enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) was used to evaluate the genetic similarity between those isolates. Transferability of the qnrS1 genes carried by the 57 strains was examined by conjugation test with the sodiumazide-resistant E. coli J53 as the recipient strain. Mutations in the quinolone resistance-determining regions (QRDR) in those strains were analyzed by PCR. Results All of the qnrS1-positive E. coli strains showed high resistance to quinolones. PMQR genes were harbored by 14 (24.6%) isolates. Extended spectrum β-lactamases (ESBLs)-producing isolates accounted for 68.4%. Mutations in the QRDR of gyrA, gyrB, parC and parE genes were found in 56 (98.2%) strains and the most frequent point mutations were S83L (89.5%) in gyrA gene, S80I (54.4%) in parC gene and P415V (28.1%) in parE gene. The qnrS1 gene was successful transferred from 13 (22.8%) isolates to E. coli J53 by conjugation. Five plasmid incompatibility groups were detected. Phylogenetic analysis showed that there were 36 (63.2%), 13 (22.8%), 1 (1.8%) and 7 (12.3%) isolates belonging to groups A, B1, B2 and D, respectively. The 57 qnrS1-positive E. coli strains were assigned to 50 ERIC types and 39 sequence types (ST) based on the results of ERIC-PCR and MLST. Conclusions Mutations in the QRDR in E. coli strains were associated with qnrS1 gene and might play a critical role in the dissemination of quinolone-resistant bacteria. Key words: qnrS; Escherichia coli; Quinolone resistance; Plasmid-mediated quinolone resistance; Quinolone resistance-determining region