Phosphate Requirements for a Whey-Based Lactic Bacteriophage Resistant Medium Under pH Control

Five strains of lactic cultures and their homologous bacteriophage races were examined for response in a whey-based medium under pH control and fortified with zero to two percent levels of added orthophosphates. One percent each of culture and phage was inoculated into each medium, which was incubated at 25 C and continuously neutralized at pH 6.3 with 20 percent NH4OH. Growth response in media was compared against growth in non fat dry milk and a commercial phage inhibitory medium (Marstar). The whey-based medium which had been frozen and thawed provided more effective growth response and greater phage protection than freshly prepared whey-based medium. Strain #3 grew optimally and was protected against phage inhibition with an added phosphate concentration of 0.5 percent whereas 0.7 percent was the required concentration in fresh whey-based medium. One strain grew optimally and was protected against inhibition in only 0.5 percent added phosphate in the fresh whey-based medium. Two strains required 0.7 to 0.75 percent and two required 1 percent. All five produced acid more rapidly in whey-based medium than in the milk or phage inhibitory medium controls. Phage inhibitory medium which was stored for four years at 25 C supported culture growth as effectively as two month old medium