The presence of genes homologous to the K88 genes faeH and faeI on the virulence plasmid of Salmonella gallinarum.

A Tn3 insertion mutation was produced in the virulence plasmid of a strain of Salmonella gallinarum which conferred avirulence by parenteral and oral routes but which was also less invasive following oral inoculation. The transposon was found to have inserted near an open reading frame (ORF) with no homologies in the data banks. This ORF was adjacent to two additional ORF's with a high degree of homology of Escherichia coli genes encoding the minor structural subunits (FaeH and FaeI) of the K88 fimbria. A similar region of homology was found by DNA-DNA hybridization on the virulence plasmids of S. pullorum, S. dublin and other S. gallinarum strains but not in the plasmids of S. typhimurium, S. enteritidis or S. choleraesuis.