A common virulence region on plasmids from eleven serotypes of Salmonella

Cured derivatives of Salmonella dublin and S. typhimurium showed reduced virulence following oral infection of mice (10(4)-10(5)-fold for S. dublin, 10(2)-fold for S. typhimurium). Large plasmids from S. dublin and S. typhimurium independently restored virulence to the cured S. dublin but truncated S. dublin plasmids with deletions in a previously identified virulence region did not. This common virulence region identified in plasmids from S. dublin and S. typhimurium was shown to be carried on plasmids from 11 other serotypes of Salmonella but was absent from 10 plasmid-containing serotypes. TnA and Tn10 were transduced from the virulence region of two TnA-insertion mutants of S. dublin and one Tn10-insertion mutant of S. typhimurium that showed diminished virulence to recipient wild-type strains of S. dublin, S. enteritidis and S. typhimurium. Each transductant showed a decrease in mouse virulence within the range 10(3)-10(5). It is therefore proposed that similar virulence determinants are expressed in different serotypes. It was also shown that integration that occurred during curing was Tn10 dependent.