Structural Studies of O-Polysaccharides from Diarrhoeal Escherichia coli

Sammanfattning: This thesis describes the structural analysis of O-polysaccharides from the Gram-negative bacterium Escherichia coli that is a diarrhoeal pathogen. The Escherichia coli serotypes investigated were O178, O171, O166 and O128. The methods used in these studies were nuclear magnetic resonance spectroscopy and component analysis.All analysed serotypes had pentasaccharide repeating units. E. coli strain O128 and O166 was shown to have the topology of four carbohydrate residues in the backbone while the 5-residue backbone is found in E. coli O178 and O171.The biological repeating units have been determined for the analysed polysaccharides and it was shown that all of the serotypes studied had a 3-substituted N-acetylgalactosamine residue at the reducing end. From this it was deduced that the terminal end of E. coli O171 and O128 have sialic acid and blood type antigens, respectively. This should make E. coli O171 and O128 less recognizable to the immune system as a foreign invader. This can result in that E. coli O171 and O128 may evade the immune system more easily.