Diplococcin Produced by Lactococcus Lactis Subsp. Cremoris

Abstract

Lactococcal strains producing inhibitory material active against other lactic acid bacteria, including Lactobacillus delbrueckii subsp. bulgaricus, were first observed by Rogers in 1928. Further interest in this area was stimulated by the research of Whitehead and Riddet (1933), who isolated from cheese milk a Gram-positive Lactococcus strain. This culture produced an inhibitor which was active against other lactic cultures and was not completely destroyed in milk by heating at 100°C for 30 min. In the same year Whitehead (1933) reported on a Lactococcus lactis subsp. cremoris strain which, when grown in milk, prevented the growth of other lactic cultures subsequently added to this milk. This inhibitory agent was proteinaceous, sensitive to the action of trypsin (but not pepsin) and restricted in activity to lactic cultures. The production of a ‘toxin’ by lactococci was implicated by Meanwell (1943) in problems associated with cheese-making. This ‘toxin’ inhibited the growth of the cheese-making bacteria and was thermostable, being destroyed only by autoclaving at 103.3 kPa pressure and not by boiling.