Characterization of the Streptococcus adjacens group antigen structure

Area of Science:

• Microbiology
• Organic Chemistry
• Biochemistry

Background:

• Serological classification of bacteria relies on unique antigens.
• Streptococci are differentiated by group antigens, including carbohydrates and amphiphiles.
• Previous studies identified key components of the Streptococcus adjacens group antigen.

Purpose of the Study:

• To chemically characterize the antigen structure of Streptococcus adjacens.
• To elucidate the repeating unit of the S. adjacens group antigen.
• To compare the S. adjacens antigen structure with other bacterial amphiphiles.

Main Methods:

• Acid hydrolysis to identify organic phosphates.
• Hydrofluoric acid cleavage to generate oligosaccharide repeating units.
• Gas chromatography-mass spectrometry of methylated, acetylated oligosaccharides.

Main Results:

• Ribitol phosphate was the sole organic phosphate detected, indicating a poly(ribitol phosphate) backbone.
• The repeating unit was identified as a trisaccharide: Galp beta 1-3Galp beta 1-4GalNac.
• N-acetylgalactosamine was linked via beta-linkage to either the C2 or C4 carbon of ribitol.
• The S. adjacens antigen is a unique amphiphile, distinct from lipoteichoic acid.

Conclusions:

• The Streptococcus adjacens group antigen possesses a unique lipid- and carbohydrate-substituted poly(ribitol phosphate) structure.
• This amphiphile structure differs significantly from the polyglycerophosphate of lipoteichoic acid found in other Gram-positive bacteria.
• The detailed chemical characterization provides a basis for understanding S. adjacens serological classification.