O antigen and H antigen- Definition and 21 Key Differences

Difference 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 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.


  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

Difference between O Antigen and H Antigen

About Author

Photo of author

Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He is doing his Ph.D. at the Central Department of Microbiology, Tribhuvan University, Kathmandu, Nepal. He was awarded the DAAD Research Grant to conduct part of his Ph.D. research work for two years (2019-2021) at Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. Sagar is interested in research on actinobacteria, myxobacteria, and natural products. He is the Research Head of the Department of Natural Products, Kathmandu Research Institute for Biological Sciences (KRIBS), Lalitpur, Nepal. Sagar has more than ten years of experience in blogging, content writing, and SEO. Sagar was awarded the SfAM Communications Award 2015: Professional Communicator Category from the Society for Applied Microbiology (Now: Applied Microbiology International), Cambridge, United Kingdom (UK).

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.