The aim of this study was to examine the presence of plasmid-mediated qnr and aac(6')-Ib-cr resistance genes among Escherichia coli and Klebsiella spp. clinical isolates obtained between 2003 and 2005 from Norway and Sweden and showed resistance and/or reduced susceptibility to nalidixic acid and ciprofloxacin, respectively. Prevalence of the qnr (1.6%) and aac(6’)-Ib-cr (14.1%) determinants was low. The qnr-genes were more prevalent in Klebsiella spp. (7.7%) than in E. coli (0.7%). qnrS1 was the most common qnr gene.The qnrS1 genes were located on at least three different plasmid backbones. Nevertheless, the qnrS1-containing area containd matching structures in all the qnrS1-positive isolates
