Core oligosaccharides of Plesiomonas shigelloides O54:H2 (strain CNCTC 113/92): structural and serological analysis of the lipopolysaccharide core region, the O-antigen biological repeating unit, and the linkage between them

The structure of the core oligosaccharide moiety of the lipopolysaccharide (LPS) of Plesiomonas shigelloides O54 (strain CNCTC 113/92) has been investigated by (1)H and (13)C NMR, fast atom bombardment mass spectrometry (MS)/MS, matrix-assisted laser-desorption/ionization time-of-flight MS, monosaccharide and methylation analysis, and immunological methods. It was concluded that the main core oligosaccharide of this strain is composed of a decasaccharide with the following structure: (see text) in which l-alpha-D-Hepp is l-glycero-alpha-D-manno-heptopyranose. The nonasaccharide variant of the core oligosaccharide ( approximately 10%), devoid of beta-D-Glcp substituting the alpha-D-GlcpN at C-6, was also identified. The core oligosaccharide substituted at C-4 of the outer core beta-D-Glcp residue with the single O-polysaccharide repeating unit was also isolated yielding a hexadecasaccharide structure. The determination of the monosaccharides involved in the linkage between the O-specific polysaccharide part and the core, as well as the presence of -->3)-D-beta-D-Hepp-(1--> instead of -->3,4)-D-beta-D-Hepp-(1--> in the repeating unit, revealed the structure of the biological repeating unit of the O-antigen. The core oligosaccharides are not substituted by phosphate residues and represent novel core type of bacterial LPS that is characteristic for the Plesiomonas shigelloides serotype O54. Serological screening of 69 different O-serotypes of P. shigelloides suggests that epitopes similar to the core oligosaccharide of serotype O54 (strain CNCTC 113/92) might also be present in the core region of the serotypes O24 (strain CNCTC 92/89), O37 (strain CNCTC 39/89) and O96 (strain CNCTC 5133) LPS.