Molecular relationships between virulence plasmids of Salmonella serotypes typhimurium and dublin and large plasmids of other Salmonella serotypes.

All studied isolates of Salmonella serotypes abortusovis (16 strains), enteritidis (30 strains), paratyphi C (29 strains), and 2 out of 10 isolates of serotype newport harboured large 54-76-Kb plasmids. No such plasmids were found in the following serotypes: agona, bovismorbificans, heidelberg, infantis, panama, paratyphi A, paratyphi B, saintpaul, senftenberg and typhi. These plasmids and the virulence-associated plasmids of Salmonella serotypes typhimurium and dublin were compared at the molecular level. Plasmids from the same serotype usually showed similar HindIII endonuclease patterns. Plasmids from different serotypes displayed markedly different cleavage patterns. Using the 3H-labelled plasmid from serotype typhimurium strain C5 as a probe, nitrocellulose filter hybridization showed that all these plasmids shared homologous sequences distributed throughout the plasmid molecule. With the S1-nuclease method, all plasmids were 61 to 88% related to the virulence plasmid of serotype typhimurium strain C5. The large plasmids in Salmonella serotypes abortusovis, enteritidis, paratyphi C, newport and the virulence-associated plasmids in serotypes typhimurium and dublin thus constitute a single group of homology and represent a family of related plasmids. We suggest that this plasmid group may contribute to the pathogenic potential of host serotypes.