A simple chromogenic test for rapid screening of Proteus and Providencia bacteria

A rapid test for detection of p-nitrophenylalanine ammonia-lyase is described. The test is performed by suspending a loopful of bacteria in 0.5 ml of a buffered 1 mM solution of p-nitro-DL-phenylalanine (PNPA). The enzymatic activity is revealed by the formation of a yellow colour after 2 hours of incubation at 35 degrees C. Out of 285 strains of different enterobacteria species positive results were shown only by 75 Proteus and Providence strains. Thus, the PNPA test can be useful for rapid screening of these enterobacteria.