Difference between O Antigen and H Antigen

 

Difference between O Antigen and H Antigen

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The surface structures of bacteria have considerable antigenic heterogeneity. Often these antigens are used as part of a serologic classification system for the bacteria.

The classification of the 2000 or so different Salmonellae is based principally on the types of the O (LPS side chain) and H (flagellar) antigens.

The antigenic type of the bacteria may be a marker for virulence, related to the clonal nature of pathogens, although it may not actually be the virulence factor.

S.N.	Character	O Antigen	H Antigen
1.	Referred to as	Somatic Antigen or Boivin antigen	Flagellar antigen
2.	Determination	Based on oligosaccharides associated with lipopolysaccharide.	Based on flagellar proteins.
3.	Cell wall	Part of the cell wall lipopolysaccharide (LPS).	Not a part of the cell wall.
4.	Composition	Polysaccharide.	Proteinaceous (Flagellin).
5.	Heat sensitivity	Somatic antigens are heat stable.	Flagellar antigens are heat-labile.
6.	Alcohol sensitivity	Resistance to alcohol	Sensitive to alcohol
7.	Formaldehyde sensitivity	Formaldehyde labile	Formaldehyde stable
8.	Extraction	Trichloro-acetic acid is used for extraction of O antigens. Since the property was first shown by Boivin, O antigen alternatively referred to as boivin antigen.	Formaldehyde is used for extraction of H antigens.
9.	Immunogenicity	Less immunogenic	Highly immunogenic
10.	Antibody levels	Produces antibody formation with low titres.	Induces antibody formation with high titres.
11.	Antibody formation	Rapid and Early	Rapid and Sustained
12.	Lifespan	Antibody levels fall off quickly.	Persists for longer periods.
13.	Antibody indicates	O antibody appears early, disappears early: indicates recent infection.	H antibody appears late, disappears late: lndicates convalescent stage.
14.	Type of agglutination reaction shown	Produces compact, chalky and granular clumps.	Produces cottony, fluffy precipitates.
15.	Reaction time	Agglutination takes place slowly	Agglutination takes place rapidly.
16.	Optimum temperature for reaction	Optimum temperature for agglutination is 55’°C.	Optimum temperature for agglutination is 37’°C.
17.	Reaction observed with	Round bottom Felix tube are used to see agglutination.	Conical bottom Dreyer’s tube is used to see agglutination.
18.	Role as virulence factor	The most important virulence factor responsible for endotoxic activity; it protects the bacteria from phagocytosis and bactericidal effect of complement.	Makes the bacteria motile, hence contributing to their virulence.
19.	Existence in phases	No phases	Flagellar antigens exist in two alternative phases- Phase I and II. Most o f them are biphasic except S. Typhi which is monophasic.
20.	Widal test	In Widal test, O antigen of Salmonella Typhi is used.	In WidaI test, H antigens of S.Typhi, S.Paratyphi A and B are used.
21.	Use in classification	Serogrouping of salmonellae is based on the O antigen.	Serogroups are differentiated into serotypes based on H antigen.