Characterization of the Natural Inhibitors in Skimmilk Affecting Lactic Acid Bacteria

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Abstract
The nature of the natural inhibitors in skimmilk which affect lactic acid produc- tion of certain streptococci was investigated by inmmnological and fractionation proce- dures. Three strains of Streptococcus cre- moris (R1, liP, and KH), susceptible to the inhibitory action of normal milk, and one resistant strain of S. lactis (C2) were utilized. Subcutaneous immunization of rabbits and a cow with S. cremoris R1 organisms produced marked specific increases in the inhibition and agglutination tilers in the blood sera of both species and in the skim- milk of the cow. Similar treatments with S. lactis C2 caused increases in the tilers of blood sera of both species, but the in- creases were not as pronounced nor as spe- cific as observed for Culture R1 and no in- creases were observed in the titers of the skinmfilk. Inhibition and agglutination li- ters of the blood sera and skimmilk of cows were not altered significantly by udder in- fusions of the cells of either R1 or C2. The inhibition and agglutination activity of skinmfilk and whey for S. cremoris R1 was specifically removed by adsorption with antigenic preparations of the homologous culture. The adsorbed factors were suc- cessfully eluted (ca. 10% recovery) from the organisms used for adsorption by use of (}.8 and 15% NaCI solutions. The proteins of whey from a cow immu- nized with S. cremoris R1 were fractionated by Sephadex gel filtration, continuous-flow paper electrophoresis, acetone, ammonium sulfate, and sodium sulfate procedures. The
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