Escherichia coli O18ac antigen: structure of the O-specific polysaccharide moiety.

The O-specific polysaccharide moiety (O18ac polysaccharide) of the O18ac antigen (lipopolysaccharide) from Escherichia coli 2980 (O18ac:K5:Fim+:H-) was isolated in pure form by degradation of the lipopolysaccharide and chromatography on Sephadex G-50. The primary structure of the O18ac polysaccharide was elucidated by composition, fragmentation procedures, methylation analysis, and nuclear magnetic resonance spectroscopy. The polysaccharide consists of repeating units of the pentasaccharide: (formula; see text) which are joined in the polymer by alpha-1,2 linkages.