The prevalence of plasmids in Danish bovine and human isolates of Salmonella dublin

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Abstract
Nine different plasmid profiles were demonstrated among 135 Danish isolates of Salmonella dublin, with 58% of the strains enclosed in the major profile group. Two strains did not carry any plasmids. The plasmid profiles of 129 strains (96%) were made up of one or more of only four plasmids of approximate sizes 98 kb, 80 kb, 4.0 kb, and 3.8 kb. There was no significant difference in the prevalence of different plasmid profile groups between isolates from cattle and man. The serovar-specific and virulence-associated 80 kb plasmid could be demonstrated in all plasmid carrying strains, but one strain carried this plasmid at a very low copy number. Five of 47 strains tested showed resistance to antibiotics (2 to sulphathiazole, 2 to streptomycin, and 1 to streptomycin and tetracycline). Only the combined streptomycin/tetracycline resistance was transferable by a 48 kb conjugative plasmid.