Incidence and properties of temperate bacteriophages induced from lactic streptococci

Abstract

63 strains of lactic streptococci isolated from commercial lactic streptococcal starter cultures were examined for lysogeny by treatment with ultraviolet light or mitomycin C. After treatment with the inducing agent, all strains, whether or not they lysed, were examined for evidence of phage release by electron microscopy. 38 strains yielded intact phages of phage particles of varying morphology. All the temperate phages had isometric heads and noncontractile tails; some had collars and structurally distinctive baseplates. Indicator host strains were found for phages induced from 7 different strains. 3 strains that released phages spontaneously yielded titers of 103 to 104 plaque forming units per ml. When strains that spontaneously released phages were grown in mixed culture with indicator strains, increased phage titers of 106 to 107 plaque forming units per ml were observed. These findings indicate that lysogenic lactic streptococcal strains may serve as a reservoir for phages that attack sensitive strains in mixed or multiple strain lactic starter cultures.