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UBC Theses and Dissertations

A structural investigation of the capsular antigens of two E. coli strains K26 and K49 Beynon, Linda M.


Diseases caused by encapsulated bacteria such as E. coli are among the most prevalent in the world. The polysaccharide capsule (K antigen) is an important factor in the virulence and pathogenicity of E. coli bacteria. Serological classification of these bacteria is also based mainly on the immunologically dominant capsular polysaccharide, due to its location at the bacterial cell surface. In order to understand the role played by the K antigens in bacterial infections, and the chemical basis of serological differentiation, the systematic structural investigation of all the capsular polysaccharides of E. coli (74 serotypes) is underway in this laboratory and others. Presented in this thesis are the structures of the K antigens of E. coli K26 and K49 serotypes. K26 capsular polysaccharide was studied using techniques such as methylation analysis, β-elimination, Smith degradation and partial hydrolysis. The oligosaccharides produced by the partial acid hydrolysis were analysed by g.c.-c.i.-m.s. To aid in the characterization of these oligosaccharides, a 'library' of relative retention times and c.i. mass spectra of authentic standards (di-, tri-, and tetra-saccharides) was prepared. The results from these analyses, together with data from n.m.r. spectroscopy of the native polysaccharide and derived oligosaccharides, allowed the following structure to be assigned to E. coli K26 polysaccharide. [Formula Omitted] E. coli K49 capsular antigen contains two amino acids, serine and threonine, amidically linked to the carboxyl group of glucuronic acid. Techniques used in the structural elucidation were raethylation analysis, acetolysis, amino acid analysis, HF hydrolysis, partial acid hydrolysis and Smith degradation. The oligosaccharides generated by the three latter methods were analysed by g.c.-c.i.-m.s. and n.m.r. spectroscopy. A bacteriophage-associated enzyme degradation of the K49 antigen yielded a product (P1) which consisted of a single repeating unit (see below). Results from the analyses of P1 and the chemically produced oligosaccharides were in agreement with the following assignment for the structure of the E. coli K49 capsular polysaccharide. [Formula Omitted]

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