Participation of Lipopolysaccharide Genes in the Determination of the Enterobacterial Common Antigen: Analysis in Salmonella Groups B and C 1

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Abstract
The enterobacterial common antigen (CA) is present in salmonellae of groups B ( S. typhimurium ) and C 1 ( S. montevideo ). Mutation at the rfe gene(s), which is required for the biosynthesis of O side chains of the lipopolysaccharide in group C 1 (S-6, 7) but not in group B (S-4, 12), destroys the capacity of the bacteria to synthesize CA. When such mutated group C 1 rfe genes (C- rfe − ) were introduced into group B strains, the hybrids also became CA − and could be restored to CA + by introduction of either C- rfe + or B- rfe + (corresponding genetic region in group B). This indicated the presence of genes for CA synthesis at the rfe site in both groups B and C 1 . In rfe − mutants of group C 1 , which were rough and CA − , the CA + phenotype could be restored by replacing the rfe − gene(s) with C- rfe + . In contrast, B- rfe + was able to support the synthesis of trace amounts of CA only, although it was sufficient to restore their ability to synthesize the S-6, 7 side chain of the lipopolysaccharide. Corresponding hybrids (B- rfe + , C- rfb + or C- rfb − ) were constructed by introducing the C- rfb genes into a group B strain; they also showed only a trace of CA reactivity.

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