Injury of Lactic Streptococci by Culturing in Media Containing High Phosphates

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Abstract
Commercial cultures of lactic streptococci, used in Cheddar cheese fermentations, were cultured in commercial bacteriophage-resistant media. Metabolic injury was determined by the difference in plate counts on 2 plating media, lactic agar and restricted lactic agar (tryptone reduced to .5%). Injury occurred with all bacteriophage-resistant media although there was considerable variation among different media. Injury was less pronounced in combinations where the culture and the bacteriophage-resistant media were from the same commercial source. Proteinase activity was diminished in all instances of injury although the extent of injury did not relate with proteinase inactivation. Proteinase was attenuated in reconstituted 11% nonfat milk solids supplemented with 1 and 2% phosphates.