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

Sammanfattning: 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).