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

Various combinations of mono- and di-basic orthophosphates were dry-blended with yeast extract, nonfat dry milk (NFDM), and the combinations of NFDM and electrodialyzed whey (EDW). These mixtures were reconstituted with tap water, heat-treated (87.8C for 45min), 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 2 HPO 4 and KH 2 PO 4 ; 2) a 4:1 mixture of NFDM and EDW with a 2% orthophosphate concentration (reconstituted basis) consisting of a 1:1 ratio of Na 2 HPO 1 and NH 4 H 2 PO 4 ; 3) a 4:1 mixture of NFDM and EDW with a 2% orthophosphate concentration (reconstituted basis) consisting of a 1:1 ratio of NH 4 H 2 PO 4 and (NH 4 ) 2 HPO 4 . 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.