Differences between O Antigen and H Antigen 5/5 (6)

Differences between O Antigen and H Antigen

Differences between O Antigen and H Antigen

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.

Differences between O Antigen and H Antigen

The major differences between O antigen and H antigen include:



O Antigen

H Antigen

1.      Referred to asSomatic Antigen or Boivin antigenFlagellar antigen
2.      DeterminationBased on oligosaccharides associated with lipopolysaccharide.Based on flagellar proteins.
3.      Cell wallPart of the cell wall lipopolysaccharide (LPS).Not a part of the cell wall.
4.      CompositionPolysaccharide.Proteinaceous (Flagellin).
5.      Heat sensitivitySomatic antigens are heat stable.Flagellar antigens are heat-labile.
6.      Alcohol sensitivityResistance to alcoholSensitive to alcohol
7. Formaldehyde sensitivityFormaldehyde labileFormaldehyde stable
8.  ExtractionTrichloro-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.      ImmunogenicityLess immunogenicHighly immunogenic
10.   Antibody levelsProduces antibody formation with low titres.Induces antibody formation with high titres.
11.   Antibody formationRapid and EarlyRapid and Sustained
12.   LifespanAntibody levels fall off quickly.Persists for longer periods.
13.   Antibody indicatesO antibody appears early, disappears early: indicates recent infection.H antibody appears late, disappears late: lndicates convalescent stage.
14.   Type of agglutination reaction shownProduces compact, chalky and granular clumps.Produces cottony, fluffy precipitates.
15.   Reaction timeAgglutination takes place slowlyAgglutination takes place rapidly.
16.   Optimum temperature for reactionOptimum temperature for agglutination is 55’°C.Optimum temperature for agglutination is 37’°C.
17.   Reaction observed withRound bottom Felix tube are used to see agglutination.Conical bottom Dreyer’s tube is used to see agglutination.
18.   Role as virulence factorThe 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 phasesNo phasesFlagellar antigens exist in two alternative phases- Phase I and II.

Most o f them are biphasic except S. Typhi which is monophasic.

20.   Widal testIn 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 classificationSerogrouping of salmonellae is based on the O antigen.Serogroups are differentiated into serotypes based on H antigen.


  1. Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi : Jaypee Brothers Medical Publishers.
  2. Tille, Patricia M., author. (2014). Bailey & Scott’s diagnostic microbiology. St. Louis, Missouri :Elsevier
  3. https://microbiologyinfo.com/difference-between-o-antigen-and-h-antigen/
  4. http://microamaze.blogspot.com/2015/10/differentiate-between-h-and-o-antigen.html

Differences between O Antigen and H Antigen

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