Polysaccharide capsules

Definition

Polysaccharide capsules are protective layers composed of carbohydrate molecules that surround the cell walls of certain bacteria. They play a critical role in bacterial virulence by helping the bacteria evade the host's immune response.

5 Must Know Facts For Your Next Test

1. The polysaccharide capsule is a major factor in the pathogenicity of bacteria such as Streptococcus pneumoniae and Neisseria meningitidis.
2. These capsules prevent phagocytosis by inhibiting the action of white blood cells.
3. Infections caused by encapsulated bacteria often result in severe diseases, including meningitis and septicemia.
4. Vaccines targeting polysaccharide capsules, like the pneumococcal vaccine, are effective in preventing bacterial infections.
5. The presence of a polysaccharide capsule can be detected using specific staining techniques like the Quellung reaction.

Review Questions

• What role does a polysaccharide capsule play in bacterial virulence?
• How do polysaccharide capsules help bacteria evade the host's immune response?
• Name one diagnostic method used to identify bacteria with polysaccharide capsules.

Related terms

Phagocytosis: The process by which a cell engulfs particles such as bacteria or other microorganisms.

Quellung Reaction: A biochemical reaction in which antibodies bind to bacterial capsules, causing them to swell and become more visible under a microscope.

Virulence Factor: Any characteristic or component of a pathogen that contributes to its ability to cause disease.