The development of differential media for the isolation of proteolytic bacteria from the rumen

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Virginia Polytechnic Institute


Two media were adapted to the culture of proteolytic bacteria from the bovine rumen. Modifications were made in the double indicator dairy medium of Donovan and Vincent (SRBP) and in the medium of Hungate for rumen bacteria (SRP). Modifications included use of plant protein suspensions, casein, and skim milk as the nitrogen sources of which skim milk was the most suitable, producing a uniformly opaque medium. Proteolytic colonies were characterized by clear zones in the medium. A third medium containing the artificial sheep-saliva salts mixture of McDougall was developed but was found unsatisfactory for the study of proteolytic organisms. Dilutions of rumen contents to 1 x 10⁻⁸/ml were made in anaerobic dilution fluids. Cultures were grown in roll tubes or bottles containing CO₂ atmosphere. All of the media used in this study repeatedly produced an average count of 40 colonies per tube with 10⁻⁸ dilutions of comminuted whole rumen ingesta as inocula. The average ratio of proteolytic to total colonies was found to be 1 to 5. Each of the media was compared for its ability to support the proteolytic isolates from the other. Minor differences in the specificity of the media were found to exist. Colonial and morphological studies of the proteolytic isolates were made.