Induction of Prophage in Lactic Streptococci Isolated from Commercial Dairy Starter Cultures1

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Abstract
Twelve commercial dairy starter cultures were examined for presence of lysogens by treating isolated strains with ultraviolet irradiation or mitomycin C. Induction of lysis in isolates from nine of the 12 commercial cultures suggested the presence of lysogenic strains. No indicator organisms were detected, but presence of phage was confirmed by electron microscopy in two of the Streptococcus cremoris isolates from the commercial cultures. The results confirm that some commercial dairy cultures produced in the United States contain phage-harboring strains.