Characterization of Plasmid-Mediated Quinolone Resistance in Gram-Negative Bacterial Strains from Animals and Humans in China.

The aim of this study was to determine the molecular epidemiology of plasmid-mediated quinolone resistance (PMQR) determinants in Escherichia coli, Salmonella enterica (Salmonella spp.), Klebsiella pneumoniae, and Proteus mirabilis. Four hundred seventy-two nonrepetitive isolates were collected from different sources in China and screened for the presence of PMQR genes (PMQRs). Then, 49 PMQR producers were selected to study the coexistence of PMQRs and other resistance genes using whole-genome sequencing (WGS). High rates of resistance to tetracycline (93.4%), nalidixic acid (81.5%), and norfloxacin (65.8%) were observed. The predominant PMQRs were aac(6')-Ib-cr (28.6%) and oqxAB (21.4%). The prevalence of PMQR determinants was significantly higher (p < 0.05) in E. coli from stockmen (55.9%, 19/34), pigs (51.1%, 70/137), and laying hens (43.1%, 28/65) than that from wild animals (21.7%, 5/23) and dairy cattle (20.1%, 5/24). WGS results showed that 89.8% of the PMQR-positive isolates co-harbored β-lactamase genes, with blaCTX-M being the dominant β-lactamase gene. In K. pneumoniae, the coexistence rate of oqxAB and qnrB with fosA, blaDHA-1, and blaSHV was significantly higher than that in P. mirabilis and E. coli. In contrast, the coexistence of qnrD and blaOXA-1 was more prominent (p < 0.001) in P. mirabilis than in the other two species. Particularly, oqxAB and mcr-1 had an obvious preference for E. coli than K. pneumonia and P. mirabilis (p < 0.001), which had not been reported in previous studies on the prevalence of PMQRs.