Plasmid-mediated resistance to multiple antibiotics in Salmonella typhi.

Two hundred forty-one strains of Salmonella typhii isolated in Lima, Peru, from October 1981 through February 1983 were tested for susceptibility to antimicrobial agents. Seventy-two strains (29.9%) were resistant to chloramphenicol and other antibiotics, including ampicillin, sulfonamides, and trimethoprim. The minimal inhibitory concentrations of 17 antimicrobial agents were determined for all of these chloramphenicol-resistant strains. Sch 25393, new beta-lactams, new quinolones, and the formulation clavulanic acid-amoxicillin were effective against all the strains. Four different resistance patterns distributed among eight phage types were observed. The 72 resistant S. typhi could transfer the resistance marker into Escherichia coli C1, and all the plasmids belonged to the incompatibility group H1.