Structural studies of Escherichia coli K26 and K46-50 using chemical and microbiological methods

The capsular polysaccharides of Escherichia coli are immunogenic and antigenic. When conjugated to a carrier protein these polysaccharides can be used as vaccines. A knowledge of the structure of bacterial capsular polysaccharides is essential for understanding antibody-antigen interaction and also for understanding the chemical basis of serological differentiation. For these reasons structural studies of some E. coli capsular polysaccharides are being undertaken in this laboratory. In this thesis a preliminary investigation into the structures of capsular polysaccharides from E. coli serotypes K/46, K/47, K/48, K49 and K50 is presented. The qualitative composition of each polysaccharide was determined by varying the hydrolytic conditions used to cleave the glycosidic bonds between the monosaccharide units. Table I shows the sugars present in each capsular polysaccharide. [Table Omitted] The ratio of the sugars in each polysaccharide was determined using methanolysis followed by reduction with sodium borohydride. The presence of amino sugars was confirmed by deamination of the hydrolyzed polysaccharide and detection of the product by g.l.c. G.l.c.-m.s., of the alditol acetates of the monosaccharides obtained by hydrolysis of the polysaccharides, was used to confirm the type of monsaccharide. present in each polysaccharide, ₁H-N.m.r. spectroscopy was utilized to confirm the presence of deoxy sugars, amino sugars and non-carbohydrate substituents. E. coli K47 and K50 capsular polysaccharides were both found to have pyruvate present as a substituent. A bacteriophage was isolated from sewage for each of E. coli K47, K48 and K49 serotypes. Phage 47 also attacked E. coli K48 and K49 bacteria. The structure of E. coli K26 capsular polysaccharide was investigated using the techniques of acid hydrolysis, carbodiimide reduction and methanolysis followed by reduction with sodium borohydride. The polysaccharide was degraded using a bacteriophage-borne glycanase. The position of cleavage found by methylation of the reduced oligosaccharide. Combination of the data obtained from the chemical analysis, n.m.r spectroscopy and the bacteriophage degradation gave the two following possible structures for the E. coli K26 capsular polysaccharide. [Formula Omitted]Science, Faculty ofChemistry, Department ofGraduat