[In vitro effect of different plants from natural grassland on rumen microbiological population]
1997
Scehovic, J. (Station federale de recherches en production vegetale de Changins (RAC), Nyon (Switzerland))
A laboratory method for the estimation of the in vitro effect of plant soluble fraction compounds on microbial growth is described. The soluble fraction of dried plant material was extracted by anaerobic Mc Dougall's buffer (artificial saliva) or by refluxing in acetone/water (1 + 1) mixture (rapid test). The anaerobic fermentation of the plant extract and strained rumen fluid (4 + 1) mixture was carried out in plastic centrifuge tubes for 24 h at 39 deg C under slow shaking. The microbial culture was isolated by centrifugation (14,000 RPM). The nitrogen content of the residual microbial pellet was determined by the Kjeldahl method. Each series of samples was accompanied by a blank in which the plant extract was replaced by a buffered nutrient medium (Thioglycollate medium U.S.P.; OXOID). Each treatment was run in duplicate. The results show that microbial growth expressed as microbial nitrogen depends upon both the energy resources available in the nutrient medium (extract) and the presence of microbial growth inhibitory compounds of which the secondary plant metabolites are likely to be the main agents. Apart from the influence of pH values and energy resources in the extract, a more or less significant alteration in microbial growth rate depending on plant species can be observed. The plant species containing phenolic polymers produce the strongest inhibitory effect on microbial growth rate. Similar inhibitory effects were observed with Trichoderma viride inoculum, cultivated on potato dextrose agar (DIFCO) mixed with the different plant extracts
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