Identification of an essential virulence region on Salmonella plasmids.

An 8 kilobase pair (kbp) fragment from the Salmonella dublin 2229 plasmid is sufficient to restore virulence for mice to cured strains of both S. dublin and S. typhimurium but only when cloned on a low copy vector. Two regions previously shown to be associated with virulence lie outside the fragment and complementation results suggest that one of these mutated regions affects expression from the 8 kbp fragment. It therefore appears that there are control elements both within and adjacent to the essential virulence fragment.