Close structural relationship of the O-antigens of various Cronobacter species containing 3-deoxy-D-manno-oct-2-ulosonic acid

Some O-polysaccharides (O-antigens) of the lipopolysaccharides of bacteria of the genus Cronobacter contain 3-deoxy-D-manno-oct-2-ulosonic acid. O-Polysaccharides of Cronobacter turicensis G3874 and Cronobacter muytjensii G3886 containing this unit were found to be structurally related to each other and to those of Cronobacter dublinensis HPB 3169 and Cronobacter sakazakii G2706 (serotype O5) studied earlier. The O-polysaccharides differ in the N-acyl group on a 3-amino-3,6-dideoxy-D-glucose residue [(R)-3-hydroxybutanoyl vs. acetyl] or in the presence or absence of the O-acetyl group on an L-rhamnose residue only. Structures of the new O-antigens were established by chemical methods and by 1D and 2D H-1 and C-13 NMR spectroscopy applied to polysaccharides and pentasaccharides obtained by mild alkaline O-deacylation and mild acid hydrolysis of the isolated lipopolysaccharides, respectively.