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Medical Definition of Lancefield classification
1. A serologic classification dividing haemolytic streptococci into groups (A to O) which bear a definite relationship to their sources, based upon precipitation tests depending upon group-specific substances that are carbohydrate in nature; e.g., Group A contains strains pathogenic for man; B, strains from mastitis in cows and from normal milk, including a few strains from the human throat and vagina; C, strains from various lower animals, including a number from cattle; D, strains from cheese; E, strains from certified milk; F, strains mainly from the human throat, associated with tonsillitis; G, strains from man, a few from monkeys and dogs; and H, K, and O, nonpathogenic strains from normal human respiratory tracts. (05 Mar 2000)