Serotype
With serotype or serovar (short form of Serovarietas ) one describes variations within subspecies of bacteria or viruses that can be differentiated with serological tests.
The serotype is a formal taxonomic means of classifying bacteria and viruses in more detail at the molecular level. To do this, the various antigens on their surface are determined (e.g. the cell wall receptors).
Position in the taxonomy
The taxonomic hierarchy for bacteria is as follows: genus> species (species)> subspecies (subspecies, ssp.)> Serotype.
The taxonomy provides for the abbreviation ssp. as well as not writing the serotype in italics. The serotype is given a capital letter.
- A full name is e.g. E.g .: Salmonella enterica ssp. enterica serotype Typhi
- Short form: Salmonella Typhi or S. Typhi
Determination of surface structures
Bacteria and viruses have structures ( antigens ) on their outside that are recognized by antibodies . The antigens differ depending on the type and strain of bacteria. In the case of pathogenic bacteria (for example Shigella , Escherichia , Salmonella ), the diversity of the antigens is used to classify them into different serotypes.
The serotype can be determined by serological tests ( e.g. ELISA ). Such serological tests are based on the specific properties of the antibodies which are directed against certain surface structures (for example polysaccharides ) of the organism.
Variability of the surface structures
If an organism occurs in only one form with regard to the structure of its surface, then it has only one serotype (antigen type). This applies to the measles virus , for example , which is why it is easy to produce a good vaccine here .
Infectious bacteria and viruses in particular come in many forms with different types of antigens. For example, streptococci ( Streptococcus pneumoniae ) are known to have over 90 different forms, which differ in the structure of their polysaccharide shell. The different forms of the envelope each represent an independent serotype, which can be determined by means of a serological test. Serotypes can occur that have an almost identical but not absolutely identical structure and are only recognized once by the same serological test, which then no longer enables them to be differentiated into two serotypes as long as another serological test does not resolve this any further.
Many extracellular (outside of cells) pathogens use the alteration of their surface structures as a strategy to avoid the immune reaction of the infected individual. This strategy can be successful for the pathogen, because the infected individual (immune system) tries to defend itself against the surface structures known / accessible to it, above all by forming antibodies.
Immune system reaction
The immune system treats each serotype of a pathogen (for example S. pneumoniae ) as if it were a completely different organism, ie each serotype leads to a type-specific immunity . This protects against a renewed infection by this serotype, but one is not preventively protected against infection by another serotype of the same pathogen. By slightly modifying their “appearance”, almost identical pathogens can infect the same individual ( host ) multiple times and cause a disease - in the case of S. pneumoniae, for example, pneumonia (and other clinical pictures).
Vaccines
For this reason, the production of a vaccine against a pathogen with many serotypes is much 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 ® ) that protects against diseases caused by seven serotypes of S. pneumoniae (4, 6B, 9V, 14, 18, 19F and 23F). This covers between 71 and 86% of those serotypes known to cause invasive pneumococcal disease in European children under two years of age.
literature
- Medical microbiology textbook , edited by Henning Brandis and Gerhard Pulverer. Founded by Heinz Reploh and Hans Jürgen Otte. 6th, revised edition. Stuttgart, Gustav Fischer Verlag, 1988.
Individual evidence
- ↑ Epidemiological Bulletin : Scientific Justification for Updating Pneumococcal Vaccination Recommendations for Seniors. RKI, December 12, 2016, accessed November 26, 2019 .