Catalase test as an aid to the identification of Enterobacteriaceae.

Although the catalase test has been used for many years for rapid differentiation of the genera of gram-positive organisms, little has been said about its use in the family Enterobacteriaceae. It was further noted that a wide variety of methods exist for the execution of the catalase test, that there is no universally accepted strength specified for the hydrogen peroxide, and that no gradations for the vigor and speed of the reaction have been mentioned. Under the conditions of the clinical laboratory, we have developed a simple, rapid, and accurate method for the catalase test that has been of great value as an aid in the identification of the Enterobacteriaceae. With 3% H(2)O(2), it was observed that Serratia, Proteus, and Providencia were vigorous catalase reactors. Only Salmonella and rare Escherichia, Enterobacter, and Klebsiella isolates were moderate catalase reactors. Escherichia and Shigella strains were mostly nonreactive, with less than one-third weekly (+) reactive, whereas most Enterobacter strains tended to be weakly reactive. Klebsiella strains were divided equally between nonreactive and weakly reactive. In practice, this test was also of great value in discerning nonpigmented Serratia cultured from the hospital environment and in detecting mixed flora containing nonspreading Proteus.