Appearance of Double-Zone Beta Hemolytic Streptococci in Blood Agar

Abstract

A certain group of [beta] hemolytic streptococci from human and animal sources form double-zones in blood agar plates refrigerated after incubation. These zones are not to be confused with those formed by a-streptococci. The cause of the phenomenon is not fully understood, but the outer zone of hemolysis is apparently due to some substance elaborated by the colony which diffuses outward into the surrounding medium and increases the fragility of the blood corpuscles so that they become laked when the temperature is reduced. The phenomenon serves to identify streptococci of this group. Their cultural characteristics, serological grouping, source and pathogenic significance are to be discussed in a forthcoming publication.