Isolation of type-specific polysaccharide antigen from group B type Ib streptococci

Area of Science:

• Microbiology
• Immunochemistry
• Glycobiology

Background:

• Group B Streptococcus (GBS) is a significant human pathogen.
• GBS is classified into serotypes based on capsular polysaccharide antigens.
• Understanding GBS antigen structure is vital for vaccine development and diagnostics.

Purpose of the Study:

• To isolate and purify the type Ib-specific polysaccharide antigen from GBS strain H36B.
• To characterize the chemical composition and structural features of the purified type Ib antigen.
• To investigate the role of sialic acid in the antigen's structure and cross-reactivity.

Main Methods:

• Enzymatic digestion of GBS strain H36B with Streptomyces albus muralytic enzymes.
• Isolation and purification of the type Ib antigen using alcohol precipitation and Sepharose chromatography.
• Structural analysis including sugar composition, molar ratios, and acid degradation studies.
• Immunological cross-reactivity assays with specific antisera and absorption studies.

Main Results:

• Purified type Ib antigen contains galactose, glucose, N-acetyl glucosamine, and sialic acid.
• Acid treatment (pH 2.0) led to significant loss of sialic acid, indicating its terminal position.
• Both native and acid-treated antigens cross-reacted with type Ia and Ic antisera due to a common Iabc determinant.
• Absorption studies confirmed the presence of both Ib-specific and Iabc determinants on the same molecule, with sialic acid not being the cross-reactive determinant.

Conclusions:

• The type Ib GBS polysaccharide antigen has a complex structure with sialic acid located terminally.
• The common Iabc determinant, responsible for cross-reactivity, is distinct from the type Ib-specific determinant and sialic acid.
• These findings contribute to the understanding of GBS serological diversity and antigen structure.