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Detection of Antagonistic and Symbiotic Relationships Among Bacteria by Diffusion Chamber Procedure

Department of Food Science and Technology, University of California, Davis 95616

ABSTRACT

Repulsion of lactic acid and adsorption of acetoin by Nuclepore membranes (pore size .4 µm) were neutralized by addition of surfactants (Tween 80 or Triton DN-65) to aqueous solutions or by broth media. The nonspecific hindrance sites on the membrane were neutralized immediately upon contact with surfactant. Slower diffusion of lactic acid in skim milk, as the concentration of lactic acid was increased, was attributed to increases in viscosity of the skim milk. The diffusion chamber procedure was tested in studies of the diffusion of lactic acid produced by lactic streptococci and antibiotic produced by Streptococcus diacetilactis DRCI. At 30 C, the pH of Elliker broth in the receiving chamber lagged 3 to 4 h behind the pH of the medium in which lactic acid was being produced. Diffusion of the antibiotic was slower in skim milk than in Elliker broth. In Elliker broth at 20 and 30 C, respectively, inhibition of Streptococcus lactis C2 in the receiving chamber became apparent at pH 6.05 (8 h) and 5.85 (4 h).