Genetic and molecular characterization of an epidemic plasmid coding for multidrug resistance in Salmonella typhimurium of human origin.

All 201 multidrug resistant Salmonella typhimurium strains isolated from epidemics in India contained nonconjugative (157 strains) or conjugative (44 strains) Inc F1me multiresistance plasmids. Two small R-plasmids of 7 MDa which coded for resistance to either ampicillin or streptomycin and sulfamethoxazole were also detected along with other plasmids. The small plasmids were members of group 1 and group 2 incompatibility groups. Restriction endonuclease analysis of conjugative (96 MDa) and nonconjugative (88 MDa) Inc F1me plasmids showed considerable similarity except for the presence of unique fragments among both the groups and the loss of fragments corresponding to the smaller size of the nonconjugative plasmid. A single Inc F1me plasmid appears responsible for various outbreaks of multiresistant S. typhimurium in different parts of India.