Decreased quinolone susceptibility in high percentage of Enterobacter cloacae clinical isolates caused only by Qnr determinants

The prevalence of qnr genes was similar in the ciprofloxacin-resistant and ciprofloxacin-susceptible Enterobacter cloacae isolates, and no amino acid change in quinolone resistance-determining regions was found in any of the 21 qnr-positive but ciprofloxacin-susceptible strains. Qnr may thus be present before the development of higher-level resistance from target mutations.