Paired and Single Strain Protease Negative Lactic Streptococci for Cheese Manufacture

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Abstract
After propagation in pH-controlled media, pairs of protease negative lactic streptococci produced acid better than the single component strains. Some protease positive pairs remained balanced with 1:1 ratios and others produced 9:1 ratios after 1 propagation. Acid production by protease negative variants was unaffected by homologous phage (i.e., remained at 100% of uninoculated controls) when paired or in single strain culture if the total numbers were .apprx. 4 times those of protease positive cells. Single strain cultures of protease positive cells lost significant activity with added phage. As phage concentration increased from 101 to 109 plaque forming units [PFU]/ml, the activity dropped from 72 to 1% of the controls. When paired, the rate of acid production improved and was 90-62% of protease negative cells as phage increased from 101 to 109 PFU/ml. Antibiotics affected acid production of both cell types, but protease positives were more inhibited. Pairing did not improve performance of either culture for added antibiotics.