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Appl Environ Microbiol. 1969 January; 17(1): 83-87
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Volatile Fatty Acids and the Inhibition of Escherichia coli Growth by Rumen Fluid¹

Department of Dairy Science, University of Illinois, Urbana, Illinois 6180 3
Department of Micorbiology, University of Illinois, Urbana, Illinois 6180 3

ABSTRACT

Concentrations of volatile fatty acids (VFA) normally found in bovine rumen fluid inhibited growth of Escherichia coli in Antibiotic Medium 3. Acetic, propionic, and butyric acids each produced growth inhibition which was markedly pH-dependent. Little inhibition was observed at pH 7.0, and inhibition increased with decreasing pH. A combination of 60 µmoles of acetate, 20 µmoles of propionate, and 15 µmoles of butyrate per ml gave 96, 69, and 2% inhibition at pH 6.0, 6.5, and 7.0, respectively. Rumen fluid (50%) gave 89 and 48% inhibition at pH 6.0 and 6.5, respectively, and growth stimulation (22%) at pH 7.0. Rumen fluid inhibitory activity was heat-stable, was not precipitated by 63% ethyl alcohol, and was lost by dialysis and by treatment with anion-exchange resins but not with cation-exchange resins. These results are consistent with the idea that VFA are the inhibitory substances in rumen fluid. Previous results which indicated that rumen fluid VFA did not inhibit E. coli growth were due to lack of careful control of the final pH of the growth medium. The E. coli strain used does not grow in rumen fluid alone at pH 7.0.

¹ Presented in part at the 66th Annual Meeting of the American Society for Microbiology, 1-5 May 1966, Los Angeles, Calif.