Structure and antigenic properties of Citrobacter freundii lipopolysaccharides

Citrobacter freundii strain E69366 was detected in a colony immunoassay with a rabbit antiserum prepared to a strain of Escherichia coli belonging to serogroup O157. Lipopolysaccharide (LPS) was shown to contain the epitope(s) involved in antibody binding. LPS prepared from strain E69366, with hot phenol contained core-LPS that migrated to the water-phase and long-chain LPS that separated into the phenol-phase. A total of 36 strains of Cit. freundii were analysed for their LPS profiles by SDS-PAGE. Sixteen could be allocated into five groups (A(3), B(7), C(2), D(2) and E(2)) based on similarities in LPS profile. The remaining strains either expressed unique SDS-PAGE profiles (18) or did not express long-chain LPS (2). All strains with a profile 'A' reacted with the antiserum prepared to E. coli O157, whereas those with other profiles did not. The two strains of Cit. freundii expressing LPS profiles designated 'E' reacted with an antiserum prepared in rabbits to E. coli O45.