Scattergram analysis to explore the emerging problem related to in vitro susceptibility test for Salmonella enterica serovar Typhi to ciprofloxacin.

Ciprofloxacin susceptibility using a disk diffusion method and minimum inhibitory concentration (MIC) value determination for 421 S. Typhi isolates showed comparable results for 296 (70%) isolates with an MIC </=0.075 mg/L. However, of the remaining 125 strains that had MIC >/=0.1 mg/L, signifying resistance, 123 (98.4%) showed discrepant results with the disk diffusion test (66 sensitive, 57 intermediately sensitive). This raises questions about National Committee for Clinical Laboratory Standards guidelines regarding the interpretative zone size for ciprofloxacin.