Note on the Susceptibility of Certain Strains of Hemolytic Streptococcus to a Streptococcus Bacteriophage

Abstract

A bacteriophage active against certain mucoid strains of hemolytic streptococci, originally isolated by Clark and Clark, was used in tests with a series of 119 strains of hemolytic streptococci which had been obtained from a variety of sources, some pathological and some normal. Of these, 37 strains were isolated from human sources, including 5 throat cultures from normal persons; 42 strains were recovered from mastitis in cows and from milk and cheese; 18 from lymphadenitis in guinea pigs; 7 from spontaneous rabbit infections with hemolytic streptococcus; 7 from pleuro-pneumonia, chronic endometritis and distemper in horses; 2 from pneumonia in foxes; 3 from streptococcus infections in swine; and 3 from a disease known as “slipped tendon” in chickens. The table shows the number of strains of hemolytic streptococcus which were susceptible to the Clark bacteriophage and the number insusceptible, as well as the source of the cultures. All susceptible strains, except the 6 of human origin, were strikingly affected by the action of this phage, and were further characterized by the formation on blood agar plates of mucoid colonies with exceptionally large zones of hemolysis. The susceptible human strains, on the contrary, did not form mucoid colonies, and were only slightly sensitive to the action of the phage and with much less regularity than the strains of animal origin. The addition of bacteriophage to susceptible cultures did not lead to the formation of plaques or “moth-eaten” colonies. This observation is in accord with the findings of others who have worked with bacteriophage active against hemolytic streptococci isolated from guinea pigs, and have rarely or never found such colonies., , Without the addition of bacteriophage, however, one of the strains in the present series occasionally showed “moth-eaten” colonies.