Structural studies of bacterial carbohydrate antigens with focus on oral commensal bacteria

90% of the total number of cells in the human body consist of the normal bacterial flora. These bacteria are mostly not harmful and, indeed, even beneficial as long as they remain physiologically outside the body, e.g., within the gastro-intestinal tract. Normally, these bacteria live in symbiosis with the host, promoting our survival by protecting the body against pathogenic bacteria and aiding in the digestion of food.

The present thesis describes the structures of the cell wall polysaccharides of Streptococcus mitis strains SK137, SK140, and SK598, which are all part of the normal bacterial flora in the oral cavity. Structural similarities between these polysaccharides and the corresponding polysaccharides of the pathogenic Streptococcus pneumoniae have been discovered and are discussed. This thesis also describes the structure of the O-antigen of the non-epidemic Vibrio cholerae serogroup 06. Epidemic cholera is caused by V. cholerae serogroups 01 and 0139 and the structural relationship between the 0-antigens of these non-epidemic and epidemic strains was investigated here.

The primary analytical techniques employed here are nuclear magnetic resonance (NMR) and mass spectrometry (MS). The products of chemical degradation of the polysaccharides with different procedures were identified by gas-liquid chromatography combined with mass spectrometry (GLC-MS) and electrospray ionisation mass spectrometry (ESI-MS).

List of scientific papers

I. Bergstrom N, Jansson PE, Kilian M, Skov Sorensen UB (2000). "Structures of two cell wall-associated polysaccharides of a Streptococcus mitis biovar 1 strain. A unique teichoic acid-like polysaccharide and the group O antigen which is a C-polysaccharide in common with pneumococci" Eur J Biochem 267(24): 7147-57
https://pubmed.ncbi.nlm.nih.gov/11106426

II. Bergstrom N, Jansson PE, Kilian M, Skov Sorensen UB (2002). "A unique variant of C-polysaccharide, which lacks phosphocholine." (Manuscript)

III. Bergstrom N, Jansson PE, Kilian M, Skov Sorensen UB (2002). "The cell wall polysaccharide from Streptococcus mitis biovar 1 strain SK140 contains a new derivative of 2,4-diamino-2,4,6-trideoxy-D-galctose." (Manuscript)

IV. Bergstrom N, Nair GB, Weintraub A, Jansson PE (2002). "Structure of the O-polysaccharide from the lipopolysaccharide from Vibrio cholerae O6. " Carbohydr Res 337(9): 813-7
https://pubmed.ncbi.nlm.nih.gov/11996834