Cell Wall Components and Antigenic Structure
Rickettsia possesses three different types of antigens as follows:
· Group-specific antigen: This is a soluble antigen presenton surface of the organisms. This is extracted from rickett-sial pathogens by repeated washings and centrifugations.
· Species- or strain-specific antigen: Species-specific orstrain-specific antigen (e.g., scrub typhus) is present in the cell wall of the bacteria.
· Alkali-stable polysaccharide antigen: This is a surface anti-gen found in some species of Rickettsia and in some strains of Proteus species (Proteus OX19, OX2, and OXK). This sharing ofantigen between Rickettsia and Proteus forms the basis of Weil– Felix test, which is employed for diagnosis of rickettsial infec-tions by demonstration of antibodies using Proteus strains.