Serotype

With serotype or serovar ( short form of Serovarietas ) is called variations within subspecies of bacteria or viruses, which are distinguishable by serological tests.

Serotype is a formal means for taxonomic classification of detailed bacteria and virus at the molecular level. To the various antigens on the surface is determined (e.g., the cell wall receptors).

Position in the taxonomy

The taxonomic hierarchy in bacteria is as follows: genus > species ( species) > subspecies ( subspecies, ssp. ) > Serotype.

The taxonomy provides the abbreviation ssp. and the serotype not italic writing. The serotype is provided with an initial capital letter.

• A full name is, eg Salmonella enterica ssp. enterica serotype Typhi
• Short form: Salmonella Typhi or S. Typhi

Determination of surface structures

Bacteria and viruses carry on its exterior structures (antigen ) that are recognized by antibodies. The antigens are different depending on the bacterial species and stem. In pathogenic bacteria (eg, Shigella, Escherichia, Salmonella ) one uses the diversity of antigens in order to classify them into different serotypes.

The serotype can be determined by serological tests (ELISA, for example). Such serological tests are based on the specific properties of the antibodies (such as polysaccharides ) are directed against the organism specific surface structures.

Variability in surface structures

Is an organism with respect to the structure of its surface in a single form, it has in accordance with only one serotype (antigen type). This is true for example for the measles virus, which is why the production of a good vaccine is a problem here.

However, in particular infectious bacteria or viruses come in many forms before with different types of antigens. So of streptococci (Streptococcus pneumoniae ) are for example 84 different forms are known which differ in the structure of their polysaccharide capsule. The various forms of the envelope each represent a separate serotype can be determined by a serological test. This serotypes can occur, which have a nearly identical, but not absolutely identical structure and are recognized by the same serological test only once, which no longer allows their differentiation into two serotypes, while another serological test not resolve this.

Many extracellular ( outside of cells exploiting dividend ) pathogens use the change of their surface structures as a strategy to evade the immune response of the infected individual. This strategy can be used for the pathogen to succeed, because the affected individual (immune ) tries to defend especially with the formation of antibodies against the known to him / accessible surface structures.

Reaction of the immune system

The immune system treats each serotype of a pathogen (eg, S. pneumoniae ) as it would be to completely different organisms, ie each serotype leads to a type-specific immunity. While this protects against re-infection by this serotype, but one is not against infection by a different serotype of the same pathogen preventively protected ( immune ). Almost identical pathogens can therefore, by modifying slightly their " appearance ", the same individual ( host ) infected multiple times and cause a disease - in the case of S. pneumoniae, for example, pneumonia ( and other diseases ).

Vaccines

For this reason, the production of a vaccine against a pathogen with many serotypes is far more difficult than against a pathogen with only one serotype. Often, a vaccine only covers the most common serotypes in the population to be vaccinated. For example, there is a vaccine against S. pneumoniae ( Prevenar ®), from disease caused by the seven serotypes of S. pneumoniae protects (4, 6B, 9V, 14, 18, 19F and 23F ). Thus, 71-86 % of those serotypes are covered, which are known to cause invasive pneumococcal disease in European children under two years.

• Microbiology