Serotype or serovar are distinct variations within a species of bacteria or viruses or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their cell surface antigens, allowing the epidemiologic classification of organisms to the sub-species level. A group of serovars with common antigens is called a serogroup.
Serotyping often plays an essential role in determining species and subspecies. The Salmonella genus of bacteria, for example, has been determined to have over 4400 serotypes, including Salmonella enterica serovar Typhimurium, S. enterica serovar Typhi, and S. enterica serovar Dublin. Vibrio cholerae, the species of bacteria that causes cholera, has over 200 serotypes, based on cell antigens. Only two of them have been observed to produce the potent enterotoxin that results in cholera: 0:1 and 0:139.
Role in organ transplantation
The immune system is capable of discerning a cell as being 'self' or 'non-self' according to that cell's serotype. In humans, that serotype is largely determined by human leukocyte antigen (HLA), the human version of the major histocompatibility complex. Cells determined to be non-self are usually recognized by the immune system as foreign, causing an immune response, such as hemagglutination. Serotypes differ widely between individuals; therefore, if cells from one human (or animal) are introduced into another random human, those cells are often determined to be non-self because they do not match the self-serotype. For this reason, transplants between genetically non-identical humans often induce a problematic immune response in the recipient, leading to transplant rejection. In some situations this effect can be reduced by serotyping both recipient and potential donors to determine the closest HLA match.
Human leukocyte antigens
|HLA Locus||# of Serotypes||Broad Antigens||Split Antigens|
|*DP and many Cw require SSP-PCR for typing.|
Serotyping of Salmonella
The Salmonella has many serotypes. At this moment, more than 2600 serotypes of Salmonella are discovered. We can identify serotypes of Salmonella by their unique code of antigens, the antigen O, composed of the extern part of the bacterium, and the antigen H, a part of the bacterium’s flagella. Each antigen is a separate variation of a structure at a molecular level. The variation can be explained by the fact that the structure is made of components that can vary for each cell, like the proteins and the lipopolysaccharides in the cell wall. There are two species of Salmonella: Salmonella bongori and Salmonella enterica, which contain serotypes. The Salmonella enterica can be subdivided into six subspecies. The process to identify the serovar of the bacterium consists of finding the formula of cell antigens which represent the variations of the bacteria. First of all, the use of the agglutination method on slides is required in order to get the antigen formula. The agglutination between the antigen and the antibody is made with a specific antisera, which reacts with the antigen to produce a mass. The antigen O is tested with a bacteria suspension from an agar plate whereas the antigen H is tested with a bacteria suspension from a broth culture. The Kauffmann-White classification scheme is used to classify the serovar depending on its antigen formula obtained with the reaction of the agglutination.
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