Medium Without Rumen Fluid for Nonselective Enumeration and Isolation of Rumen Bacteria

TLDR

Medium 10, a rumen fluid‑agar substitute, replaces rumen fluid with hemin, trypticase, yeast extract, and a volatile fatty acid mixture that mimics rumen fluid composition. Removing or altering trypticase, yeast extract, or volatile fatty acids in medium 10 markedly reduces colony counts, and diet‑dependent differences in colony numbers and strain composition were observed, yet medium 10 consistently supported growth of the predominant rumen bacteria and proved suitable for their enumeration and isolation.

Abstract

Colony counts which approximated those in a habitat-simulating, rumen fluid-agar medium (RFM) were obtained in medium 10, a medium identical to the RFM except for the replacement of rumen fluid with 1.5 × 10 -6 m hemin, 0.2% Trypticase, 0.05% yeast extract, and a 6.6 × 10 -2 m volatile fatty acid mixture qualitatively and quantitatively similar to that in rumen fluid. Single deletion of Trypticase, yeast extract, or the volatile fatty acid mixture from medium 10 significantly reduced colony counts. Colony counts were also reduced when medium 10 was modified to contain higher concentrations of Trypticase or volatile fatty acids. Significant differences were found between colony counts obtained from diluted rumen contents of animals fed a cracked corn-urea diet, and the colony counts obtained from animals fed either a cracked corn-soyean oil meal or an alfalfa hay-grain diet. Qualitative differences were found between the predominant bacterial strains isolated from rumen contents of animals fed cracked corn diets and strains isolated from animals fed alfalfa hay-grain. Regardless of differences in the predominant flora associated with diet, medium 10 and the RFM supported growth of similar bacterial populations. The results show that medium 10 is suitable for enumeration and isolation of many predominant rumen bacteria.