Urease activity of Proteus species in filtered compared with autoclaved urea media.

Hatch, M. H. (Brown University, Providence, R.I.) and C. A. Stuart. Urease activity of Proteus species in filtered compared with autoclaved urea media. J. Bacteriol. 83:1119-1123. 1962.-Urease activity of a number of strains of four Proteus species was compared in a filtered medium and an autoclaved medium. Various amounts of saline suspensions of the organisms were used as inocula for the two media. In some experiments Seitz-filtered yeast extract was added to autoclaved basal urea medium. All tests were incubated at 35 C and read 8, 12, 24, and 48 hr after inoculation. The filtered medium appeared superior to the autoclaved medium, particularly when small inocula were employed. Under these conditions, many tests with all four species were negative in the autoclaved medium at 48 hr, in contrast to 100% positive reactions in the filtered medium with all species except P. morganii. The experiments in which Seitz-filtered yeast extract was added to autoclaved basal urea medium suggested that both destruction of growth-promoting substances in the yeast extract and production of conditions inhibitory for growth during autoclaving might be involved in the differences observed between the two media.