Visualization of bacterial polysaccharides by scanning transmission electron microscopy

Area of Science:

• Microbiology
• Biochemistry
• Electron Microscopy

Background:

• Neisseria meningitidis causes bacterial meningitis.
• Capsular polysaccharides are key virulence factors.
• Understanding polysaccharide structure is crucial for vaccine development.

Purpose of the Study:

• To visualize the morphology of purified Neisseria meningitidis capsular polysaccharides (groups A, B, and C).
• To investigate potential relationships between polysaccharide structure and antigenicity.

Main Methods:

• High-resolution Scanning Transmission Electron Microscopy (STEM) was employed.
• Purified capsular polysaccharides from Neisseria meningitidis groups A, B, and C were analyzed.

Main Results:

• Meningococcus A and C polysaccharides presented as spheroidal macromolecules (~200 Å diameter).
• Meningococcus B polysaccharide appeared as filaments (400-600 Å length).
• Filaments were occasionally observed with Meningococcus A and C, suggesting complex structures.

Conclusions:

• Distinct morphologies were observed for different Neisseria meningitidis polysaccharide groups.
• A proposed model suggests filaments arranged into spheroidal micelles for groups A and C.
• Meningococcus B polysaccharide is characterized as a short, flexuous filament.
• The study proposes a link between polysaccharide morphology and its antigenicity.