Culture medium for differentiation of Proteus and Providencia groups from other enterobacteria by the l-tryptophan desaminase

Abstract

A culture medium with l-tryptophan was studied in order to differenciate the groups Proteus and Providencia from other enterobacteriaceae. By testing 642 samples of microorganisms using this culture medium both groups Proteus and Providencia developed a yellow-brownish colour after 18 hrs of incubation at 37°C. The enterobacteriaceae of other groups determines no change upon the culture medium. The reliability of this method was proved by comparing with the Singer & Volcani technique giving the following results: 144 samples of Proteus and 113 of Providencia gave positive desaminase reaction with both techniques; 385 samples or enterobacteriaceae of other groups showed negative desaminase reaction with both techniques. Twenty one (21) samples of Serratia showed negative reaction with the Singer & Volcani method and a faint positive reaction with the studied technique. Such a faint reaction can be considered as negative for desaminase. The technique proved to be sensitive and specific.