Structure of a Kdo-containing O polysaccharide representing Proteus O79, a newly described serogroup for some clinical Proteus genomospecies isolates from Poland

• 32 Proteus genomospecies 5/6 strains were isolated from patients in the Lodz area.
• Seven Proteus genomospecies 5/6 strains were classified into a new serogroup, O79.
• Structure of the O polysaccharide of a representative O79 strain, 11 B-r, was established.
• The structure established is unique among known bacterial polysaccharides.
• The O polysaccharide was acid-labile owing to the presence of Kdo in the main chain.

From 41 Proteus genomospecies strains isolated in Poland, seven displayed similar serospecificity in ELISA with intact and adsorbed O antisera as well as in Western blot. The cross-reacting strains were found to belong to Proteus genomospecies 5/6 and classified into a new Proteus serogroup, O79, which seems to be widespread among Proteus genomospecies clinical isolates in Lodz, Poland. The O polysaccharide of the lipopolysaccharide of a representative O79 strain, 11 B-r, was studied by chemical analyses and 1H and 13C NMR spectroscopy, and the following structure of the repeating unit was established:→4)-α-d-GlcpNAlaAc-(1→5)-α-Kdop-(2→2)-α-d-Glcp-(1→3)-β-d-GlcpNAc-(1→where AlaAc indicates N-acetyl-l-alanyl and Kdo indicates 3-deoxy-d-manno-oct-2-ulosonic acid.The O polysaccharide was unstable under mild acidic conditions and cleaved by acid-labile linkages of Kdo residues to yield a tetrasaccharide with Kdo at the reducing end. The structure established is unique among Proteus O polysaccharides, which is in agreement with the lack of any significant cross-reactivity for the lipopolysaccharide of strain 11 B-r and O antisera against strains of all known Proteus O serogroups and vice versa.

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