Nalidixic acid resistance in Salmonella strains with decreased susceptibility to ciprofloxacin isolated from humans in Turkey.

The aim of this study was to evaluate the value of nalidixic acid resistance as an indicator of decreased susceptibility to ciprofloxacin (MIC = 0.125 - 1 mg/L) in Salmonella isolates from humans (n = 620) in Turkey. One isolate was found to be resistant, and the remaining isolates were susceptible to ciprofloxacin with the Clinical and Laboratory Standards Institute breakpoints; however, 75 isolates (12.1%) had decreased susceptibility. Resistance to nalidixic acid was observed in 76 (12.3%) isolates in the disk diffusion test. Seventy-four of these isolates had decreased susceptibility, one was fully resistant, and one isolate was susceptible to ciprofloxacin. One isolate with decreased susceptibility to ciprofloxacin was intermediate to nalidixic acid. Screening with 30-microg nalidixic acid disks had a sensitivity of 98.6% and a specificity of 99.8% for determination of decreased susceptibility to ciprofloxacin.