Evidence of coordinate regulation of virulence in Salmonella typhimurium involving the rsk element of the 95-kilobase plasmid.

Integration of the Salmonella typhimurium virulence plasmid into the chromosome reduces mouse virulence, serum resistance, and HeLa cell adhesion-invasion while prolonging lag time in minimal medium. The proposed virulence plasmid regulatory element, rsk, partially restores virulence and fully restores the other three phenotypes to wild-type levels. Plasmid curing reduces virulence without affecting the other phenotypes. rsk has no apparent effect on the cured strain.