Plasmid encoded multi-drug resistance in Salmonella typhi from Pakistan.

Twenty-five isolates of Salmonella typhi made from cases of typhoid fever during 1990-1991 in Rawalpindi and Islamabad, were examined. All isolates were resistant to chloramphenicol, ampicillin, tetracycline, streptomycin, sulphamethoxazole and trimethoprim, but were sensitive to nalidixic acid, ofloxacin, ciprofloxacin, cefuroxime and cefotaxime. A single large 98 MDa plasmid was identified in all the isolates. The plasmid was self-transferable and encoded resistance to chloramphenicol, ampicillin, tetracycline, streptomycin, sulphamethoxazole and trimethoprim. Restriction endonuclease analysis patterns after EcoRI and HindIII digestion of the 98 MDa multi-drug resistance plasmids from each of the S. typhi isolates and transconjugants were the same.