A New Medium for the Detection of Urea-splitting Organisms.

Bacteriological laboratories engaged in diagnostic or research problems concerning pathogenic enteric bacilli, namely, the Salmonella and Shigella groups, invariably find that members of the genus Proteus are by far the most misleading. A dependable, easily interpreted, routine differential test medium for screening the latter group of bacilli becomes desirable. Urease production is a characteristic activity of the genus Proteus (Bergey et al., 1939). The hydrolysis of urea by urease has been described by Werner (1923) as "an 'alkaline fermentation' during which the 'carbonate of ammonia' was formed." Rustigian and Stuart (1941) recommended a urea medium for the detection of this enzyme activity. A modification of the latter medium has been described by Anderson (1945). Since one of the products of the splitting of urea is the formation of ammonia, Rustigian and Stuart suggested that phenol red indicator be employed to detect this alkaline change colorimetrically. Howell and Sumner (1934) reported that the pH optimum for urease activity upon 2.5 per cent urea is 6.9 with phosphate buffer. The present report describes a new medium for the detection of urea-splitting organisms. Colorimetric changes are sharp and permit easy interpretation of results.