In Salmonella heidelberg the copy number of the Salmonella-specific insertion element IS200 was found to vary from four to six. All strains tested contained at least one common insertion site which was serovar specific, and most strains contained three common sites. Concurrent analysis of plasmids indicated that all insertion sequence copies were chromosomally located, and also supported the equivalence of an IS200 fingerprint and clonality. Seven intra-serovar clonal lines were thereby identified. One of these was associated with human infections, including septicaemias. Another was associated with chicken as a host: all these strains also carried a unique plasmid of 23 MDa, which was typed as a member of the IncX group. The chromosomal fingerprint of a third clone showed it to be a descendant of the chicken line marked by a single IS200 transposition. One or two representatives of four other clonal lines were identified. These lines of S. heidelberg could be related by divergent evolution, and the most recent relatives conformed to a continuous branching process model of IS200 transposition. This insertion sequence provided a highly discriminatory molecular marker of the S. heidelberg chromosome, and two of the seven clonal lines so identified were associated with distinct clinical/epidemiological contexts.

SUMMARYAn analysis of genotype was made for representative strains of Salmonella dublin. The collection consisted primarily of strains isolated from humans in England and WVales. 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 168 ribosomal RNA genes, a phylogenetic marker. Two clones of S. dublin (SdRI and SdRII) which shaied an identical IS200 profile, were identified on the basis of restriction fragment length polymorphism at the 168 rRNA locus. With one exception, all strains harboured a 52 MDa plasmid which contained a conserved 37 kbp Hind III fragment homologous to the spvBC mouse-virulence genes of S. typhimuriurn. However, a single plasmid-free strain of SdRI, isolated from a patient with septicaemia exhibited no spv 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. IN Phenotypic subtyping with bacteriophages has provided highly discriminatory schemes for salinonella serovars of epidemniological imnportance such as S. enteritidis, S. typhinurium, and S. typhi. However, in England and Wales the relatively low incidence of S. dublin in humans has not justified the development of such a scheme for this serovar. Plasmid profile typing is also inappropriate for S. dublin, since most isolates contain a single large serotype-specific plasmid of 52 inegadaltons (AIDa) [3] implicated in virulence of the organism for BALB c mice. A * Corresponlding authlor.

SUMMARYA collection ofSalmonella enteritidisstrains isolated in Switzerland (1965–90) was characterized. The phage type and plasmid profile of isolates were compared with the copy number and insertion loci of the DNA insertion element IS200. Three clonal lines ofS. enteritidiswere identified by IS200profile; the various phage types were subtypes reproducibly associated with one of these lines. All human and poultry isolates contained a 38 Mda plasmid which hybridized with a mouse virulence-associated gene probe. InS. enteritidis, the IS200profile is a race-specific molecular marker of the chromosome, and may be particularly applicable for studying the epidemiology of less common serovars.

The copy number and location of the insertion sequence IS200, a mobile DNA element, was established across a collection of Salmonella berta. All strains contained one common site, assumed to be present in the evolutionary ancestor of this serovar. With one exception, all strains, including recent outbreak isolates from the UK and sporadic isolates of world‐wide distribution, were representatives of a single genotypic clone which carried three common IS200 insertion sites. This clone has acquired diverse combinations of plasmids, reflecting its actual or recent distribution and host. A single isolate, belonging to a second, minor genotypic clone was characterised by two IS200 insertion sites.