Associative Relationships between Bifidobacteria and Lactobacilli in Milk

The associative relationships between bifidobacteria and lactobacilli in milk were investigated, using Bifidobacterium breve, B. infantis, Lactobacillus casei and L. acidophilus as the organisms. The growth and acid production in the four mixed cultures were determined and compared to those of pure culture for 24hr of incubation at 37°C. Main results obtained were as follows: 1. In case of incubation with B. breve and L. casei, or with B. infantis and L. casei, the numbers of B. breve, B. infantis and L. casei were higher than those of pure culture, and acid productions in the mixed cultures were markedly greater than those of expected value. In view of the above results, it is concluded that associative relationships are established between bifidobacteria and L. casei. 2. The viable cell counts of L. acidophilus in the mixed cultures with B. breve, or with B. infantis were a little lower than in its pure culture, whereas increased acid productions were observed in the mixed cultures. 3. The addition of heat-treated and unheated cell-free filtrates obtained from lactobacilli cultures to the milk inoculated with bifidobacteria gave appreciable stimulation for the growth and acid production of bifido-bacteria over those of control and the degree of stimulation was maximum with the addition of unheat filtrates. 4. The fractions of lactobacilli extracts on Sephadex G-100 column which were active for the reduction of pH of the milk inoculated with bifidobacterla contalned proteolytlc enzymes, aminopeptidase, β-galactos1dase, and phospho-β-galactosidase.