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 collect-ed from Fujian Medical University Union Hospital. Plasmid-mediated quinolone resistance ( PMQR) genes [qnrA, qnrB, qnrC, qnrD, aac(6′)-Ib-cr, qepA and oqxAB] andβ-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 sim-ilarity 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 conjuga-tion. 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.
ABSTRACT
In this study, we investigated the presence of plasmid-mediated quinolone resistance (PMQR) genes among 101 ciprofloxacin-resistant urinary Escherichia coli isolates and searched for mutations in the quinolone-resistance-determining regions (QRDRs) of the DNA gyrase and topoisomerase IV genes in PMQR-carrying isolates. Eight isolates harboured the qnr and aac(6')-Ib-cr genes (3 qnrS1, 1 qnrB19 and 4 aac(6')-Ib-cr). A mutational analysis of the QRDRs in qnr and aac(6')-Ib-cr-positive isolates revealed mutations in gyrA, parC and parE that might be associated with high levels of resistance to quinolones. No mutation was detected in gyrB. Rare gyrA, parC and parE mutations were detected outside of the QRDRs. This is the first report of qnrB19, qnrS1 and aac(6')-Ib-cr -carrying E. coli isolates in Brazil.