Antibiotic resistance profiles and molecular epidemiology of Salmonella typhimurium and S. dublin, mainly from cattle.

Among 130 strains of Salmonella typhimurium and 191 strains of S. dublin, all isolated from cattle in the early 1980s, 80% and 63%, respectively, were resistant to one or more (up to three) antibiotics. Monoresistance to sulphonamides was most common. In 169 strains of the two serotypes from 1985 the antibiotic resistance load was of a similar size. The latter batch was not studied with respect to plasmids. In the strains from 1980 and 1981 the plasmid load was analysed by conjugation, transformation, extraction of plasmid DNA and subsequent electrophoresis in agarose gels. Plasmid DNA from 38 strains was further analysed by restriction with endonuclease EcoRI. On the basis of this the strains were classified into four groups: two of S. typhimurium, one of S. dublin and one group of both serotypes. This suggested that dissemination of strains and plasmids mainly occurred through clonal spread of strains.