Structure and serological specificity of the K13-antigenic polysaccharide (K13 antigen) of urinary tract-infective Escherichia coli.

The primary structure of the K13-antigenic polysaccharide (K13 antigen) of Escherichia coli O6:K13:H1 was elucidated by composition, periodate oxidation, Smith degradation, and methylation analysis. The polysaccharide consists of a repeating sequence of 3-linked ribofuranose and 7-linked 3-deoxymannooctulosonic acid (KDO). About 50% of the KDO residues are O-acetylated at position 4 or 5. Measurement of the optical rotary dispersion indicated that in aqueous solution the K13 polysaccharide assumes a secondary structure in which the carboxyl groups of KDO are engaged. The serological specificity of the K13 polysaccharide is expressed through KDO and its O-acetyl substituent, the ribose unit being antigenically silent. There are two populations of anti-K13 antibodies one directed against the charged region of the KDO and the other against the O-acetyl groups.