Structural studies of the Escherichia coli K93 and K53 capsular polysaccharides.

The structures of the Escherichia coli K93 and K53 capsular polysaccharides have been investigated by chemical and spectroscopic methods. The repeating unit of both polymers was found to be----3)-beta-D-Galf-(1----f)-beta-D-GlcAp-(1. The O-5 and O-6 atoms of D-galactose are acetylated in the repeating unit of the K93 polymer, but only O-2 is acetylated in the K53 polymer. The K93 polysaccharide is cross-reactive with the Neisseria meningitidis Group A capsular polysaccharide (of known structure). The K53 polysaccharide, although structurally similar to that from K93 organisms, does not cross-react with the Group A polymer.