Evaluation of Commercial Phage Inhibitory Media

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Abstract
Seven commercially prepared brands of lactic streptococcal phage inhibitiory media were studied. Comparisons between media were of buffering capacity, ability to support lactic streptococcal growth and ability to suppress bacteriophage replication. Nonfat milk was a control. Only 2 of the media were adequate in preventing phage proliferation, and the capacity of any 1 medium to stop phage proliferation and growth was related to its buffering capacity. Compositional data indicated that those media which were most effective in preventing phage replication contained sufficient nutrients to support streptococcal growth, thus overcoming the effects of high phosphate and/or citrate concentrations which depressed growth. The medium which supported the best streptococcal growth as compared to nonfat milk was intermediate in suppressing phage proliferation. The 4 most effective phage inhibitory media each contained citrate buffers and the 3 least effective media lacked this compound; the most effective medium also contained hydrolyzed cereal solids to enhance streptococcal growth.