Structural and immunological studies of the Escherichia coli K7 (K56) capsular polysaccharide.

The structure of the Escherichia coli K7 capsular polysaccharide has been investigated by a combination of chemical and spectroscopic methods. The Structure of the repeating unit of the polymer was found to be goes to 3)-beta-D-ManNAcA-(1 leads to 4)-beta-D-Glc-(1 goes to ; the O-6 atom of the D-glucosyl residue in the repeating unit is acetylated. The K7 polysaccharide is cross-reactive with the Streptococcus pneumoniae type 3 polysaccharide, the structure of which had previously been determined; our n.m.r. studies of the S. pneumoniae type 3 polysaccharide are in accord with this structure. The E. coli K7 and K56 capsular antigens have been shown by serology and 13C-n.m.r. spectroscopy to be identical.