Single colony isolates of lactic streptococcal strains, most of which have been utilized for cheese-making in New Zealand, were u.v.-irradiated and their growth response was followed optically. All 45 strains showed either lysis or impairment of growth. Their concentrated, bacteria-free supernatants were examined by electron microscopy for the presence of phage particles. Intact phages were observed in most lysates, while disrupted phage parts were found in the remaining lysates. Plaque-forming ability was demonstrable in a few cases. Lysogenization of a different strain by one of the phages detected by this technique was attempted. Similarities and differences with respect to lytic phages which have been isolated for these same strains in New Zealand cheese factories are discussed in relation to the possible origin and control of phages.


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