Structures of a unique O-polysaccharide of Edwardsiella tarda PCM 1153 containing an amide of galacturonic acid with 2-aminopropane-1,3-diol and an abequose-containing O-polysaccharide shared by E. tarda PCM 1145, PCM 1151 and PCM 1158 Original Research A

Lipopolysaccharides of four strains of Edwardsiella tarda were degraded by mild acid hydrolysis, and the released O-polysaccharides were isolated by GPC and studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including 2D 1H, 1H COSY, TOCSY, ROESY, 1H, 13C HMBC, HSQC and HSQC-TOCSY experiments. The O-polysaccharide from E. tarda PCM 1153 was found to contain d-GalA, d-GlcNAc, d-Gal and 2-amino-1,3-propanediol (GroN). In the tetrasaccharide repeating unit, GroN is amide-linked to one of the GalA residues, and Gal is non-stoichiometrically 2- or 3-O-acetylated (∼45% at each position): Three other E. tarda strains examined (PCM 1145, PCM 1151 and PCM 1158) share the following O-polysaccharide structure: where Abe indicates 3,6-dideoxy-d-xylo-hexose (abequose). This structure resembles those of Citrobacter freundii O22 (PCM 1555) and Salmonella enterica O4. In accordance with the structural data, SDS–PAGE and immunoblotting of the lipopolysaccharides with anti-C. freundii O22 serum demonstrated that the O-antigens of the three E. tarda strains are serologically identical to each other and to the O-antigens of C. freundii O22 and S. enterica O4.