Enumeration and selective isolation of rumen spirochetes.

Enumeration by means of light microscopy showed that from 0.4 x 10(8) to 2.0 x 10(8) spirochetes were present per ml of bovine rumen fluid. Viable cell counts yielded slightly lower values, ranging from 0.1 x 10(8) to 1.2 x 10(8) spirochetes per ml of rumen fluid. The antibiotic rifampin, which served as a selective agent for rumen spirochetes, was added to agar media used in the estimation of viable spirochete numbers in rumen fluid. Morphologically diverse spirochetes were isolated from rumen fluid by means of a procedure involving the use of rifampin as a selective agent in agar media. The strains isolated represented seven morphological types of spirochetes differing in cell size, cell coiling pattern, and number of periplasmic fibrils per cell. Electron microscopy showed that the number of periplasmic fibrils present in the different morphological types of rumen spirochetes ranged from 2 to more than 20 per cell. The results of this study indicate that the bovine rumen is a highly favorable environment for a number of morphologically diverse spirochetes.