Structural determination of the O-antigenic polysaccharide from the verocytotoxin-producing Escherichia coli O176

Cross-peaks of low intensity from α-linked mannopyranosyl residues were present in the 1H, 1H TOCSY NMR spectra and further analysis of these showed that they originate from the terminal part of the polysaccharide. Consequently, the biological repeating unit has a 3-substituted N-acetyl-d-galactosamine residue at its reducing end. The repeating unit of the E. coli O176 O-antigen is similar to those from E. coli O17 and O77, thereby explaining the reported cross-reactivities between the strains, and identical to that of Salmonella cerro (O:6, 14, 18).