Dry-Blended Phosphate-Treated Milk Media for Inhibition of Bacteriophages Active Against Lactic Streptococci

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Abstract
Various combinations of mone- and dibasic orthophosphates were dry-blended with yeast extract, nonfat dry milk (NFDM), and with combinations of NFDM and electrodialyzed whey (EDW). These mixtures were reconstituted with tap water, heat treated (87.8 C for 45 min), and cooled. The ability of these media to prevent proliferation of bacteriophages active against lactic streptococci while not hindering host culture activity was determined. As a result of this study, three combinations were found that will inhibit most or all of the indicated bacteriophages: 1) a 3:2 mixture of NFDM and EDW with a 2% orthophosphate concentration (reconstituted basis) consisting of a 1:1 ratio of Na?HPO4 and KH2PO4; 2) a 4:1 mixture of NFDM and EDW with a 2% orthophosphate concentration (reconstituted basis) consisting of a 1:1 ratio of Na,HPO4 and NH4H2PO4; 3) a 4:1 mixture of NFDM and EDW with a 2% orflio-phosphate concentration (reconstituted basis) consisting of a 1:1 ratio of NH4H2PO4 and (NH4),HPO4. All of the mixtures contained 0.32% yeast extract (reconstituted basis). The first two formulae inhibited five of six phages examined, whereas, the third effectively inhibited all six. None of the three mixtures was inhibitory to the host lactic streptococci.