Characterization of multidrug-resistant, qnrB2-positive and extended-spectrum-β-lactamase-producing Salmonella Concord and Salmonella Senftenberg isolates

To characterize plasmids and resistance genes of multidrug-resistant (MDR) Salmonella Senftenberg and Salmonella Concord isolated from patients in the Netherlands. The resistance genes of four MDR Salmonella isolates (three Salmonella Concord and one Salmonella Senftenberg) were identified by miniaturized microarray, PCR and sequencing. Plasmids were characterized by S1 nuclease-PFGE and PCR-based replicon typing (PBRT). Linkage between plasmids and genes was determined by conjugation experiments and microarray analysis. The genetic relationship between the three Salmonella Concord isolates was determined by XbaI-PFGE. A large variety of resistance genes was detected, including qnrB2 and the beta-lactamase genes bla(TEM-1) and bla(SHV-12) in all isolates; moreover all Salmonella Concord isolates also harboured bla(CTX-M-15). Salmonella Senftenberg harboured a large IncHI2 plasmid. The three Salmonella Concord isolates harboured two large plasmids typed as IncHI2 and IncA/C. We detected the first plasmid-mediated MDR Salmonella isolates in the Netherlands harbouring both qnr and extended-spectrum beta-lactamase (ESBL) genes. In Salmonella Senftenberg one large plasmid (IncHI2) and in Salmonella Concord two large plasmids (IncHI2 and IncA/C) were responsible for the multidrug resistance.