Structural studies of the O-antigen polysaccharide from the enteroinvasive Escherichia coli O164 cross-reacting with Shigella dysenteriae type 3.

The structure of the O-antigen polysaccharide from Escherichia coli O164 has been determined. Nuclear magnetic resonance spectroscopy together with component and methylation analyses of lipid free polysaccharide were the principal methods used. The sequence of the sugar residues could be determined by NOESY and heteronuclear multiple bond connectivity NMR experiments. It is concluded that the polysaccharide is composed of a pentasaccharide repeating unit with the following structure: structure: see text]. Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) was performed on intact lipopolysaccharide and from the resulting molecular mass, the O-antigen part was estimated to contain approximately 24 repeating units. The nature of the previously reported cross-reactivity of this O-antigen to those of Escherichia coli O124 and Shigella dysenteriae type 3 is discussed.