Factors Inhibiting and Stimulating Bacterial Growth in Milk: An Historical Perspective

Abstract

The chapter illustrates that the growth of bacteria in milk, because of its complex nature, is not as simple as it may at first appear. It seems that the net bacterial growth measured is the result of the organisms resisting inhibitory systems present in the milk and being stimulated by some unknown substances also present. The role of antibodies in the inhibition of lactic acid bacteria is not clear. The role that they play in milk is similar to that played by antibodies to groups A, B, C, and D streptococci in rabbit serum. Another possible mechanism causing the inhibition of lactic acid bacteria involves a lack of Fe 2+ . Lactic cultures, in the absence of sufficient Fe 2+ may not be able to produce sufficient NADH peroxidase, or other enzymes necessary to decompose hydrogen peroxide. The natural stimulator(s) in milk for lactic acid bacteria is unknown. An essential nitrogen source has been suggested as the stimulator, as have sulfydryl-containing substances. Further work is required to determine what the nature of the stimulator is in the cream fraction in milk. A fully integrated understanding of the growth of bacteria in milk awaits elucidation.