Molecular analysis of the virulence locus of the Salmonella dublin plasmid pSDL2

Abstract

The virulence properties of various non-typhoid Salmonella serotypes depend on the presence of large plasmids 60–100 kb in size. We have shown previously that the virulence region on the 80 kb plasmid pSDL2 of Salmonella dublinLane maps within a 14kb SalI fragment. In this report we show that an 8.2kb region within this fragment is sufficient to express lethal disease in BALB/c mice. Sequence analysis of this segment revealed six sequential open reading frames designated vsdA–F, which encode putative proteins of 13–65kDa. Deletion analysis and location of Tn5-oriT inserts which abolish virulence suggest that vsdA, vsdC, vsdD and vsdE are essential for virulence expression. Downstream of vsdF we discovered a locus involved in stable plasmid maintenance. Deletion of that region resulted in plasmid multimerization and instability.