Probiotics: Growth-Promoting Factors Produced by Microorganisms

Several species of protozoa, during their logarithmic phases of growth, produce substances that prolong the logarithmic phase in other species. The effect is not as striking as the inhibition of growth caused by antibiotics, but a consistent 50-percent increase in growth has been obtained with Tetrahymena pyriformis in response to a factor produced by Colpidium campylum.