Phenylalanine Deaminase Test- Principle, Procedure, Results


Phenylalanine deaminase test, also known as phenylpyruvic acid (PPA) test, is a biochemical test used to determine the ability of bacteria to produce an enzyme called phenylalanine deaminase. This enzyme catalyzes the oxidative deamination of the amino acid phenylalanine, which means it removes the amine group (NH2) from phenylalanine and produces phenylpyruvic acid and ammonia as products .

Phenylpyruvic acid is a key intermediate in the metabolism of phenylalanine and tyrosine, two essential amino acids that are involved in the synthesis of various proteins, hormones, neurotransmitters and pigments. Phenylpyruvic acid can react with a chelating agent called ferric chloride, which forms a green-colored complex that can be detected visually . This color change is the basis of the phenylalanine deaminase test.

The phenylalanine deaminase test was first developed by Hendriksen in 1950 to differentiate Proteus spp., which are bacteria that can produce phenylalanine deaminase, from other members of Enterobacteriaceae, which are bacteria that cannot produce this enzyme. Later, Ewing and his team formulated a medium containing phenylalanine to test the bacterial capacity to deaminate phenylalanine oxidatively. In 1971, Ederer and his associates developed a disc method to rapidly detect the bacteria`s ability to produce both urease and phenylalanine deaminase enzymes. These methods have been modified over time and are now widely used in microbiology laboratories for identification and differentiation of various bacterial species.

The phenylalanine deaminase test is especially useful for distinguishing Proteus spp., Morganella spp. and Providencia spp., which are positive for this test, from other Enterobacteriaceae, which are negative for this test . These bacteria are commonly found in soil, water, plants and animals, and some of them can cause infections in humans, such as urinary tract infections, wound infections, septicemia and meningitis. Therefore, the phenylalanine deaminase test can help in the diagnosis and treatment of these infections by providing information about the bacterial identity and susceptibility to antibiotics.