Vi antigen

Definition

The Vi antigen is a virulence factor found in some strains of Salmonella, particularly Salmonella Typhi. It is a polysaccharide capsule that helps the bacteria evade the host immune response.

5 Must Know Facts For Your Next Test

1. The Vi antigen is primarily associated with Salmonella Typhi, the causative agent of typhoid fever.
2. It enhances the bacterium's ability to resist phagocytosis and complement-mediated killing.
3. Vaccines targeting the Vi antigen can provide immunity against typhoid fever.
4. Presence of the Vi antigen can be detected using specific serological tests in laboratory settings.
5. Loss or mutation of the Vi antigen may reduce virulence but can enhance recognition by the immune system.

Review Questions

• What role does the Vi antigen play in the pathogenicity of Salmonella Typhi?
• How does the presence of the Vi antigen affect the immune evasion strategies of Salmonella Typhi?
• Why is the Vi antigen a target for vaccine development against typhoid fever?

Related terms

Salmonella Typhi: A bacterial pathogen that causes typhoid fever, often characterized by high fever and gastrointestinal symptoms.

Phagocytosis: The process by which certain cells engulf and digest microorganisms and cellular debris.

Complement System: A part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear pathogens.