5 key Differences between O and H Antigen Explained

O Antigen: Also known as the somatic antigen, the O antigen is a component of the lipopolysaccharide (LPS) layer present in the outer membrane of Gram-negative bacteria.

H Antigen: The H antigen, also known as the flagellar antigen or the phase antigen, is a protein component of the bacterial flagellum. It is responsible for the motility of bacteria through the surrounding environment.

Difference between O and H Antigen:

Characteristic H Antigen O Antigen
Sensitivity Heat labile, sensitive to alcohol Heat stable, remains unaffected by alcohol
Antigen Extraction Formaldehyde treatment Trichloroacetic acid treatment
Composition Protein complex Phospholipid-protein-polysaccharide complex
Agglutination Reaction Produces large, fluffy, loose clumps Produces compact, chalky, granular clumps
Immunogenicity Highly immunogenic, induces antibody formation Less immunogenic, produces antibody formation with low titres
Stability Susceptible to denaturation under harsh conditions Relatively stable under harsh conditions
Cross-Reactivity May cross-react with related antigens Less likely to cross-react with related antigens
Antigenicity May exhibit variability in antigenicity Relatively consistent antigenicity
Clinical Significance Can result in false negative reactions Less prone to causing false negative reactions
Specificity Found in a wide range of bacterial species

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