Somatic antigens of Pseudomonas aeruginosa. The structure of the O-specific polysaccharide chains of Ps.aeruginosa O:2 (Lanyi) lipopolysaccharides.

Structural and immunochemical studies have been performed on the O-specific antigens of two serologically related types of Pseudomonas aeruginosa O:2a,b and O:2a,c (Lanyi's classification). The O-specific polysaccharide chains of the two serotypes were shown to be acidic polysaccharides composed of repeating trisaccharide units consisting of L-rhamnose, N-acetyl-D-quinovosamine and N-acetyl-L-galactosaminuronic acid residues. Based on 1H and 13C nuclear magnetic resonance spectroscopy, data of methylation analysis and selective solvolysis with hydrogen fluoride, the repeating unit of the O:2a,c O-specific polysaccharide was assigned the following structure: leads to 4)LGalNAcA(alpha1 leads to 3)DQuiNAc(alpha1 leads to 3) LRha(alpha1, where GalNAcA = N-acetylgalactosaminuronic acid, QuiNAc = N-acetylquinovosamine and Rha = rhamnose. The O:2a,b O-specific polysaccharide had the same structure of the trisaccharide repeating unit but was distinguished by the presence of O-acetyl groups on 70-80% of the rhamnose residues in position 2. The O-acetyl groups were located both by methylation with methyltrifluoromethane sulphonate and by comparison of the 13C nuclear magnetic resonance spectra of the native and O-deacetylated polysaccharides. Serological studies revealed the determinant role of the O-acetyl groups in the O-antigen O:2a,b and suggested the O-factor 2b to be related to the 2-O-acetyl-L-rhamnose residue, whereas the O-factor 2c was probably determined by the nonacetylated rhamnose residue. The dominant moiety of the determinant 2a common to the two antigens was obviously presented by the N-acetyl-L-galactosaminuronic acid residue.