It defines the antigenic types of a particular species of bacterium. Bacteria differ in their antigenic make-up; separation into the different types using specific antigen is called serotyping; while separation into groups using specific antigen is called serogrouping. Separation into serotypes allows for better characterization and understanding the epidemiology of a particular strain of bacterial species. It helps in defining strains of public health importance.

Maybe this paper could help you:

http://jcm.asm.org/content/39/3/924.full.pdf+html