It is the science that studies serum and immune responses that are evident in serum

When microorganisms enter the body, proteins called antibodies bind with the specific bacteria in order to identify the microorganisms. The antibodies are stimulated to bind because of certain antigens in the microorganism. Antigens can differ among bacteria of the same species and also be the same in bacteria of different species.

Antibodies can be put into antiserum which can then be administered to identify microorganisms based on antibodies that bond. Depending on which antibodies bond, the antigens of the bacteria can be determined. As mentioned before, same species of bacteria can have different antigens, so these differing strains of bacteria depending on antigen can allow us to classify them into serotypes.

Slide agglutination test, bacterium is administered with antiserum, if bacteria clumps with serum, test is positive, if spreads evenly with serum, test is negative. Serological testing can show similarities between different bacteria depending on similar antigens. Serological testing was used to identify two stereotypes of streptococcus progenes that were flesh eating bacteria.

Another two types of serological testing is ELISA or Enzyme Linked ImmunoSorbent Assay, where different wells of antibiotics have samples of a bacterium dumped in them to see which one reacts. The other is Western Blotting where a bacterium/virus has its proteins separated by electrophoresis. The separated proteins are blotted onto a filter where serum taken from a patient will be tested on the blot; if the proteins and serum combine there is a reaction, and anti-human serum is used to wash away non binding antibodies from the original human serum.