Antimicrobial susceptibility of Salmonella typhi to quinolones & cephalosporins

Antimicrobial sensitivity testing was carried out for 85 isolates of S. typhi by disc diffusion and microbroth dilution for estimation of minimum inhibitory concentration (MIC). The drugs used included amoxycillin, chloramphenicol, ciprofloxacin, ofloxacin, gentamicin, netilmicin, cefuroxime, ceftizoxime, cefoperazone and ceftazidime. Ninety three per cent of our isolates were resistant to amoxycillin and chloramphenicol but total susceptibility was seen to quinolones and aminoglycosides. We also found that 3 per cent of our isolates were resistant to cephalosporins and 23 per cent were in the intermediate range with an MIC of 12.5 or 25 mu g/ml to these drugs. In spite of decreased efficacy, the strains continued to be fully susceptible to ciprofloxacin as could be seen from the extended dilutions in microbroth dilution tests. The study also revealed that there was lack of correlation between the two methods of sensitivity testing for cephalosporins. We feel that the development of resistance of S. typhi to third generation cephalosporins is a finding worth consideration for further studies.