Assessing the molecular basis of transferable quinolone resistance in Escherichia coli and Salmonella spp. from food-producing animals and food products.

Enterobacteriaceae resistant to quinolones frequently arise in animals, being easily disseminated through the food-chain. The aim of this study was to investigate the presence of plasmid-mediated quinolone resistance (PMQR) determinants in Salmonella spp. (n=183) and Escherichia coli (n=180) isolates, collected from food-producing animals and food products among swine, poultry, rabbits and cattle. All isolates were subjected to antimicrobial susceptibility testing and molecular screening of PMQR determinants. β-Lactamase-encoding genes, and the quinolone resistance determining region (QRDR) of gyrA, gyrB, parC and parE genes were also investigated in PMQR-positive isolates. Plasmid characterization was performed by conjugation, followed by replicon-typing. Genetic relatedness of PMQR-positive E. coli was examined by Multilocus Sequence Typing, while Salmonella was previously serotyped. The association of mobile genetic elements and PMQR was investigated through PCR mapping assays. Overall, 4.1% (15/363) isolates harbored qnrB2 (n=3), qnrB19 (n=3), and qnrS1 (n=9) genes. All but one isolate presented one to four mutations in QRDR of gyrA or parC genes, which is consistent with the range of MIC values detected (0.19-64 mg/L) for ciprofloxacin; 60% (9/15) of qnr-harboring isolates were non-susceptible to β-lactam antibiotics which was justified by the presence of β-lactamases from TEM (TEM-1, n=8; TEM-135, n=1) and SHV (SHV-108, n=1) families. Analysis of mobile genetic elements revealed that qnr genes were detected nearby relevant genetic elements like intI1, ISEcl2, IS26 and ISCR1 and enclosed in diverse Inc. type plasmids. This study illustrated the existence of Qnr-producing E. coli and Salmonella from food-producing animals, associated to specific mobile elements that might mediate their transference between species and among distinct settings.