What is the Lancefield grouping system and how does it work?

Rebecca Lencefield (1895-1981) was a renowned American
microbiologist at the Rockefeller Institute for Medical Research in New York City.  Her
career was spent as professor of microbiology at Columbia
University.

Lancefield is best known for her system for
grouping hemolytic streptococci.  The grouping is done using serology (antibody-antigen
reactions) based on the carbohydrate antigens on the surfaces of the various
streptococcal species.

A partial Lancefield grouping of the
hemolytic streptococci is as follows.  Please see the reference for a complete
list.

Group A:  Streptococcus
pyogenes

Group B:  s.
agalactiae

Group C:  s. equisimilis, s. equi, and s.
dysgalactiae

Group D:  enterococci, s.
bovis