Yeasts and moulds in the bovine rumen

Summary: Only small numbers of fungi were found in the rumen fluid of cattle cultured on agar plates at 39°C, the counts being up to 3500 yeast colonies/ml, with a similar number of mould colonies. However, considerably larger numbers of yeast colonies appeared on plates incubated at 25°C. Nine species of yeasts were isolated belonging to Candida (including corresponding species of Pichia), Trichosporon, Torulopsis, Kluyveromyces, Saccharomycopsis, and Hansenula. The predominating species were Candida krusei, Trichosporon cutaneum and Trichosporon capitatum. The most common moulds were members of the Mucoraceae, of which Absidia corymbifera, A. ramosa, and Mucor pusillus were identified. Aspergillus fumigatus was isolated frequently. The fungal content of rumen fluid seemed to be dependent on the diet of the animal, and no particular fungal flora could be associated with the rumen per se. The predominating Candida krusei, and also the rarely-isolated species Torulopsis pintolopesii and Kluyveromyces bulgaricus, could reproduce under anaerobic conditions in vitro, but another commonly occurring yeast, Trichosporon capitatum, was unable to grow under the same conditions. The majority of yeast cells were obviously destroyed during passage through the alimentary tract, whereas large quantities of moulds could be excreted in a viable state.