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Characterization of the Natural Inhibitors in Skimmilk Affecting Lactic Acid Bacteria¹

Department of Dairy Technology, The Ohio Agricultural Research and Development Center, The Ohio State University, Columbus

ABSTRACT

The nature of the natural inhibitors in skimmilk which affect lactic acid production of certain streptococci was investigated by immunological and fractionation procedures. Three strains of Streptococcus cremoris (R1, HP, 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 titers in the blood sera of both species and in the skimmilk of the cow. Similar treatments with S. lactis C2 caused increases in the titers of blood sera of both species, but the increases were not as pronounced nor as specific as observed for Culture R1 and no increases were observed in the titers of the skimmilk. Inhibition and agglutination titers of the blood sera and skimmilk of cows were not altered significantly by udder infusions of the cells of either R1 or C2.

The inhibition and agglutination activity of skimmilk and whey for S. cremoris R1 was specifically removed by adsorption with antigenic preparations of the homologous culture. The adsorbed factors were successfully eluted (ca. 10% recovery) from the organisms used for adsorption by use of 0.8 and 15% NaCl solutions.

The proteins of whey from a cow immunized with S. cremoris R1 were fractionated by Sephadex gel filtration, continuous-flow paper electrophoresis, acetone, ammonium sulfate, and sodium sulfate procedures. The inhibitory factor was found to be associated with the immune globulin fraction. The evidence supports the conclusion that the inhibitory action of skimmilk for lactic acid-producing streptococci is due, to a significant extent, to the presence of specific antibodies.

¹ Article no. 38-66, The Ohio Agricultural Research and Development Center. This investigation was supported in part by Public Health Service Grant no. EF-00101 from the Division of Environmental Engineering and Food Protection and in part by Hatch Funds.

² Present address: Department of Animal Science, Texas A&M University, College Station, Texas.