Plasmid studies of Salmonella typhimurium phage type 179 resistant to ampicillin, tetracycline, sulphonamides and trimethoprim.

Sixteen strains of Salmonella typhimurium phage type 179 were referred to the National Health Institute, Wellington, New Zealand, from 1977 to 1979. This phage type had not been observed here before 1977. All strains were resistant to ampicillin, several were also resistant to tetracycline, and several were resistant to ampicillin, tetracycline, sulphafurazole and trimethoprim. All resistances could be transferred to Escherichia coli K 12. Plasmids from these strains and their transconjugants were characterized by agarose gel electrophoresis. It appears that resistance to sulphafurazole and trimethoprim is carried on a plasmid with a molecular weight of 5 . 2 Mdal and that resistance to ampicillin and tetracycline is carried on a plasmid with a molecular weight of approximately 60 Mdal.