Isolation and Characterization of Streptococcus agalactiae Bacteriophage

Temperate and virulent phages are known to occur in streptococci of groups A, C and D (Bradley & Kay, 1960; Brailsford & Hartman, 1968; Brock, 1964; Follett, 1967; Kjems, 1960; Rogers & Sarles, 1963). No phage has been reported for group B streptococci; we report the isolation of such a phage and give some of its properties. Cultures of streptococci were isolated from cow's milk and identified as strains of Streptococcus agalactiae serologically and by the CAMP test (Christie, Atkins & Munch-Peterson, 1944). Phage suspensions were obtained from 16 hr culture of S. agalactiae by centrifugation in a model L. Spinco centrifuge (5000 g) for 15 min. followed by filtration of the supernatant fluid through a 0.45 µ pore-size membrane filter (MilliporeCorp., Bedford, Mass, U.S.A.). A drop of the filtrate was put on an agar plate seeded with test organisms. Phage activity was indicated by clear plaques after incubation. Phage stocks were plaque-purified and stored at 4°.