The distribution of plasmids among a representative collection of Scottish strains of salmonellae

The distribution of plasmids was studied in a representative collection of salmonella strains which comprised 98 Salmonella typhimurium and 96 other serotypes. Plasmids were detected in 72% of strains (mean 1.3 plasmids/strain) and individual strains harboured between 0 and 7 plasmids. They were more common among S. typhimurium than other serotypes (incidence 92 and 53%; mean 1.9 and 0.8 plasmids/strain respectively). Although a higher proportion of S. typhimurium (33%) were antibiotic-resistant compared to other serotypes (14%) the evidence presented indicated that R-plasmids were not responsible for the difference observed in the number and distribution of plasmids in these strains. These results were discussed in comparison with similar studies of Escherichia coli and other enteric genera.