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.
The major differences between O antigen and H antigen include:
|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.|
|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.|
- Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi : Jaypee Brothers Medical Publishers.
- Tille, Patricia M., author. (2014). Bailey & Scott’s diagnostic microbiology. St. Louis, Missouri :Elsevier