Interactions of Lactobacillus and Propionibacterium in Mixed Culture

Four species of Lactobacillus ( L. acidophilus , L. casei , L. delbrueckii and L. bulgaricus ) were paired with four species of Propionibacterium ( P. pentosaceum , P. shermanii , P. acidipropionici and P. freudenreichii ) and were grown in pure and mixed culture to assess associative interactions. Experiments were performed using a defined synthetic medium with glucose as an energy source and casamino acids as a nitrogen source. A differential respirometer (32°C) and Warburg flasks were used; growth, carbon dioxide, and acid production were measured. Fifteen of the 16 paired cultures had less growth, acid, and carbon dioxide produced than pure culture controls. In some pairs, both cultures were inhibited by mixed cultivation while in others only the Propionibacterium was inhibited. In several mixtures, the Lactobacillus culture was apparently unaffected by mixed culturing. In P. shermanii and L. acidophilus mixed culture, a beneficial synergistic effect on growth, carbon dioxide, and volatile and nonvolatile acid production was observed. Little lactate accumulated in the mixed culture medium and was apparently used as an energy source and resulted in increased carbon dioxide and acid production by the P. shermanii .