Abstract
An analysis of genotype was made for representative strains of Salmonella dublin. The collection consisted primarily of strains isolated from humans in England and Wales, and were of both intestinal and extra-intestinal origin. Three genetic elements were characterized by DNA hybridization. They were the spvBC genes, extrachromosomal virulence determinants, the salmonella-specific insertion sequence IS200, and the 16S ribosomal RNA genes, a phylogenetic marker. Two clones of S. dublin (SdRI and SdRII) which shared an identical IS200 profile, were identified on the basis of restriction fragment length polymorphism at the 16S rRNA locus. With one exception, all strains harboured a 52 MDa plasmid which contained a conserved 3.7 kbp Hind III fragment homologous to the spvBC mouse-virulence genes of S. typhimurium. However, a single plasmid-free strain of SdRI, isolated from a patient with septicaemia exhibited no spc homology. In SdRI there was no observable genotype distinction between strains causing gastroenteritis or bacteraemia. In contrast, none of the strains of SdRII were from cases of bacteraemia, and all human isolates of this clone were from cases of gastroenteritis.