Phenylalanine Deaminase Test : Principle, Procedure, Results and Uses

Phenylalanine deaminase test also known as phenylpyruvic acid (PPA) test is used to test the ability of an organism to produce enzyme deaminase.  This enzyme removes the amine group from the amino acid phenylalanine and produces phenylpyruvic acid (PPA) and ammonia i.e. oxidative deamination of phenylalanine.  Phenylalanine agar, also known as phenylalanine deaminase medium which contains DL-phenylalanine and nutrients is used as a test medium.

Phenylalanine Deaminase Test


  1. Take or prepare a phenylalanine deaminase agar medium
  2. Inoculate the phenylalanine slant (with a loop on the surface) with a test organism.
    Note: If you are using the test medium i.e. phenylalanine agar for the first time use positive (Proteus vulgaris) and negative control (Escherichia coli) to check the efficacy of the test medium.
  3. Incubate the test medium at 37°C for overnight.
  4. Add 4-5 drops of 10% aqueous ferric chloride (FeCl3) solution to the slant.
Phenylalanine deaminase test results (microbugz)


  1. Positive test: Production of green colour (Phenylpyruvic acid thus formed reacts with ferric chloride producing a green colored compound thus turning the medium dark green). Proteus sp., Morganella sp., Providenica sp give positive PPA test.
  2. Negative: No colour change (medium remains straw/yellow color; no PPA to react with ferric chloride).

Uses of Phenylalaine Deaminase Test

Phenylalaine deaminase test is used to differentiate members of the genera Proteus, Morganella, and Providencia (+ve)  from other members of Enterobacteriaceae which give negative results.