Role of a large plasmid of Salmonella typhi encoding multiple drug resistance

National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road, Calcutta-700010, * Command Pathology Laboratory (E.C.), Alipore, Calcutta, India Correspondence hould be sent to: Dr R. Kumar. Received March 15, 1990 Accepted August 3, 1990 Summary. Twenty isolates of Salmonella typhi from cases of typhoid during the 1989–1990 epidemic in Calcutta were examined. Most isolates (84% of all isolates in the epidemic) were resistant to chloramphenicol, ampicillin, tetracycline and streptomycin but were sensitive to nalidixic acid and ciprofloxacin. Plasmids of 120 kb and 14 kb were identified amongst the multi-drug resistant isolates of S. typhi. However, there was no plasmid in the antibiotic-sensitive isolates. The 120-kb plasmid was transferable and transconjugants were resistant to chloramphenicol, ampicillin, tetracycline and streptomycin. Restriction endonuclease analysis patterns after Eco RI digestion of the 120-kb antibiotic-resistance plasmids from the S. typhi isolates and transconjugants were similar.