Isolation and characterization of Streptococcus agalactiae bacteriophage

Department of Large Animal Medicine, Obstetrics and Surgery, New York State Veterinary College, Cornell University, Ithaca, New York, 14850, U.S.A. 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°. Received 28 August 1968; accepted 19 March 1969.