Trend of increasing levels of minimum inhibitory concentration of ciprofloxacin to Salmonella typhi.

The minimum inhibitory concentration (MIC) of ciprofloxacin has been determined in 193 strains of S. typhi isolated during January and July each year from March 1991 to July 1995. While all strains remained within established range of susceptibility, a clear trend of increase of MIC values with time was observed. During the first four study periods, all strains had MIC values below 0.031 microgram/ml; during the fifth and sixth, 3 strains had a higher value namely 0.125 microgram/ml. During the last four, 14 strains showed MIC values of 0.25 microgram/ml. Thus an increase in MIC of ciprofloxacin to S. typhi has been observed over the years.