The Relationship of Serologic Groups A, B, and C of Lancefield to the Type of Hemolysis Produced by Streptococci in Poured Blood Agar Plates

Abstract

1,179 strains of hemolytic streptococci isolated in the general bacteriology laboratory were studied in standardized poured horse-blood agar plates at 24 and 48 hrs. at 37, and after 24 hrs.'' refrigeration, and on the surface of similar blood agar plates. Colonies in poured blood agar produced more characteristic colonies than surface colonies on similar plates. 1104 of these strains sero-logically belonging to Lancefield Group A all had similar characteristics. At the end of 48 hrs. in the incubator at 37[degree] there was a clear, definite hemolyzed zone approximating 3.5 mm. around the colony. 23 strains of Lancefield Group B in poured blood agar plates showed at the end of 48 hrs. an area of incomplete hemolysis about 2.5 mm. surrounded by a faint but definite band of slight hemolysis. 19 serologic Group C streptococci presented a characteristic type of hemolysis. At the end of 48 hrs. there was a 3-5 mm. zone of clear hemolysis which became progressively less hemolytic toward the periphery, the total zone of hemolysis extending up to 9 mm. A few strains of Groups D, E, F, G, H, and K were studied but no group specific type of hemolysis was found. Many of these strains could not be distinguished from Group C in poured blood agar plates. Groups A and B possess definite distinguishing zones of hemolysis, in poured blood agar plates. Group C produces a characteristic hemolysis which, however, could not be distinguished from various strains in higher groups.