Detection of decreased susceptibility to fluoroquinolones in Salmonella spp. by five different methods including real-time polymerase chain reaction (PCR)

Detection of Salmonella spp. isolates showing decreased susceptibility to fluoroquinolones has become important owing to the increasing prevalence of these strains and their association with treatment failure. Nalidixic acid agar dilution, nalidixic acid disk diffusion, MicroScan automated system and real-time polymerase chain reaction (PCR) (LightCycler) followed by melting temperature (Tm) analysis are compared with ciprofloxacin agar dilution as suitable methods to detect decreased susceptibility to fluoroquinolones in 100 Salmonella spp. isolates. Three minor discrepancies were found for nalidixic acid disk diffusion, one minor discrepancy was found for nalidixic acid agar dilution and Tm analysis, and one major discrepancy was found for MicroScan. Nalidixic acid disk diffusion was confirmed as a good screening method. Tm analysis is a rapid and accurate method for detecting decreased susceptibility to fluoroquinolones due to gyrA mutations in Salmonella spp.