Streptocci Lancefield Grouping Test

The Streptococcus Grouping Latex Test (Strep) is a latex slide agglutination test used for the identification of laboratory streptococci isolates into groups A, B, C, D, F, and G according to the Lancefield classification scheme.

Streptococci possess specific polysaccharide cell wall antigens which permit further classification of the bacteria into groups according to the Lancefield classification scheme. The Lancefield precipitin technique is a conventional method that is laborious and time-consuming. The combination of latex agglutination technology and the availability of a rapid enzyme extraction method has revolutionized the Lancefield grouping procedure. The group specific antigen is extracted into solution by the action of an enzyme. When the group-specific antigen (in the released form) is mixed with the appropriate latex reagent, distinct agglutination patterns will be observed. In the absence of the group-specific antigen, the latex reagent will remain as a smooth suspension. The Streptocci Lancefield Grouping test is based on this principle for the grouping of Streptococci in cultures obtained from solid phase media as well as from liquid culture after subculturing onto plate media.