Bacteriocin of a Group B Streptococcus: Partial Purification and Characterization

The production of bacteriocin-like inhibition by two of 135 strains of group B streptococci was demonstrated during the growth of these organisms on solid nutrient media. Although a variety of gram-positive organisms was susceptible, none of a wide range of different gram-negative strains was inhibited. The active substance produced by one of these strains was extracted from cultures grown on solid media (Todd-Hewitt agar) and was shown to be bactericidal in action. This bacteriocin (streptocin B(1)) was partially purified by ammonium sulfate precipitation followed by gel filtration and ion-exchange chromatography. Production of the bacteriocin was repressed by addition of certain fermentable carbohydrates to the basic medium and enhanced by the addition of yeast extract. The bacteriocin was shown to exist in two distinct and interconvertible physical forms: a basic unit of molecular weight 10,000 and an aggregate having a molecular weight of over 200,000. The bacteriocin was inactivated by proteolytic enzymes and, although labile in alkali, it was stable to boiling in mild acids.