Colicinelike substances, bacteriocines, are produced by many strains of Group A and non-Group A streptococci. Bacteriocines were detected by their inhibitory action on the growth of 2 Group A strains which served as indicators.

Streptococcal bacteriocines were demonstrable on agar plates only if the bacteriocine-producing strain and the indicator lawn were alive and actively growing. The inhibitory substances diffused slowly into the agar during the course of growth. Bacteriocines were not replicated in the zones of inhibition in which the microorganisms of the indicator strains were killed. Attempts by various methods to separate bacteriocines from living bacteria were unsuccessful.

In contrast to the many strains which produced bacteriocines, only a few strains of Group A streptococci were suitable to serve as indicators for bacteriocine production. Strains of Group A streptococci of the nephritogenic types 12, 4, and 49 produced bacteriocines most consistently. Strains of other types, isolated from patients with acute rheumatic fever or from children with uncomplicated streptococcal pharyngitis, produced bacteriocines infrequently. Among non-Group A streptococci bacteriocine-positive and bacteriocine-negative strains occurred in approximately equal numbers.

It was shown by Wilson and by Bernheimer that the majority of the strains of the nephritogenic types were leukotoxic and produced DPNase. Bacteriocine production is another common characteristic property of these special types.

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