Hey, what is the difference between serogroup and serotype?

 

Serogroup is a classification above the serotype. A tricky bit is that the original definitions and classifications have shifted in various species due to the use of modern genetic tools. However, in the medical field, the immunoresponse (or the identificaiton of antigens) is still the gold standard (in academic research there are calls for a more unified view, however).

If we use Salmonella again, The sergroups are based on the presence of specific O antigens (part of the cell wall). But each serogroup is further divided into serotypes based on flagellar antigens.

Thanks for the reply! Could you help me out with another one, what's a strain?

 

I believe a strain is a particular genetic variant of a microorganism. Sort of like how different breeds of dogs, which can look different and act differently, etc., are all just sub-types of the same species. 

It should be noted that in microbiology a strain can be distinguished by minimal differences. Everything not being genetically identical (i.e. clonal) can be considered a different strain. For example, every mutation you introduce into a given bacterium results in a new strain.