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Objectives This study was initiated to collect retrospective information on the occurrence of plasmid-mediated quinolone resistance (PMQR) in Salmonella enterica and Escherichia coli isolates in Europe and to identify the responsible genes. Methods Databases of national reference laboratories containing MIC values for Salmonella and E. coli isolated between 1994 and 2009 in animals, humans, food and the environment from 13 European countries were screened for isolates exhibiting a defined quinolone resistance phenotype, i.e. reduced susceptibility to fluoroquinolones and nalidixic acid. PCR and sequence analysis were performed to identify the responsible PMQR genes. Results Screening of databases of 13 European countries resulted in a selection of 1215 Salmonella and 333 E. coli isolates. PMQR genes were identified in 59% of the Salmonella isolates and 15% of the E. coli isolates selected. In Salmonella, qnrS1 (n¿=¿125) and variants of qnrB (n¿=¿138) were frequently identified, whereas qnrA1 (n¿=¿3) and aac(6')-1b-cr (n¿=¿3) were rarely found. qnrD was detected in 22 Salmonella isolates obtained from humans and animals. In E. coli, qnrS1 was identified in 19 isolates and qnrB19 was found in one isolate. No qnrC or qepA genes were detected in either Salmonella or E. coli. Conclusions This study shows the occurrence and dissemination of PMQR genes in Salmonella and E. coli in Europe with a defined quinolone resistance phenotype. We also report the first detection of qnrD in Salmonella collected in Europe.

Objectives: The aim of this study was to identify and characterize plasmids carrying qnrS1, qnrB2 and qnrB19 genes identified in Salmonella strains from The Netherlands. The identification of plasmids may help to follow the dissemination of these resistance genes in different countries and environments. Methods: Plasmids from 33 qnr-positive Salmonella strains were transferred to Escherichia coli and analysed by restriction, Southern blot hybridization, PCR and sequencing of resistance determinants. They were also assigned to incompatibility groups by PCR-based replicon typing, including three additional PCR assays for the IncU, IncR and ColE groups. The collection included isolates from humans and one from chicken meat. Results: Five IncN plasmids carrying qnrS1, qnrB2 and qnrB19 genes were identified in Salmonella enterica Bredeney, Typhimurium PT507, Kentucky and Saintpaul. qnrS1 genes were also located on three further plasmid types, belonging to the ColE (in Salmonella Corvallis and Anatum), IncR (in Salmonella Montevideo) and IncHI2 (in Salmonella Stanley) groups. Conclusions: Multiple events of mobilization, transposition and replicon fusion generate the complexity observed in qnr-positive isolates that are emerging worldwide. Despite the fact that the occurrence of qnr genes in bacteria from animals is scarcely reported, these genes are associated with genetic elements and located on plasmids that are recurrent in animal isolates.