Plasmid-mediated quinolone resistance in Salmonella isolated from patients with overseas travelers' diarrhea in Japan.

Twenty-eight of the 302 Salmonella strains isolated from patients with overseas travelers' diarrhea who were examined at Kansai Airport Department Station during the 6-year period between 2001 and 2007 showed decreased susceptibility to both nalidixic acid (NA) and ciprofloxacin (CPFX) (MIC of NA, 16-64 microg/mL; MIC of CPFX, 0.064-2.0 microg/mL). These 28 strains revealed no variations in the quinolone resistance-determining region; however, 25 of the strains showed retention of the qnr gene. The qnr-retaining Salmonella belonged to 6 serotypes, and 21 and 4 of the 25 strains showed qnrS1 and qnrS2, respectively. The most common serovar was S. Corvallis (17 strains).