Lancefield grouping is a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls. [1] The system, created by Rebecca Lancefield, was historically used to organize the various members of the family Streptococcaceae, which includes the genera Lactococcus and Streptococcus , but now is largely superfluous due to explosive growth in the number of streptococcal species identified since the 1970s. [2] However, it has retained some clinical usefulness even after the taxonomic changes, [1] and as of 2018, Lancefield designations are still often used to communicate medical microbiological test results.
The classification assigns a letter code to each serotype. There are 20 described serotypes assigned the letters A to V (excluding E, I and J). [3] Bacteria of the genus Enterococcus , formerly known as group D streptococci, were classified as members of the genus Streptococcus until 1984 and are included in the original Lancefield grouping. [4] Many—but not all—species of streptococcus are hemolytic. Notably, enterococci and Streptococcus bovis (Lancefield group D) are not beta-hemolytic. [5] Though there are many groups of streptococci, the principal organisms that are known to cause human disease belong to group A ( Streptococcus pyogenes), group B ( Streptococcus agalactiae ), group C/G ( Streptococcus dysgalactiae) both members of group D (Streptococcus gallolyticus and Streptococcus infantarius, both members of the Streptococcus bovis group), and two alpha-haemolytic groups that lack the Lancefield carbohydrate antigen: Streptococcus pneumoniae and viridans streptococci. [2] [3]