Phenylalanine deaminase is seen in some genera of Enterobacteriaceae but not others and can aid in identification of an isolate.
Genera with phenylalanine deaminase:
(1) Proteus
(2) Morganella
(3) Providencia
Phenylalanine deaminase converts phenylalanine to phenylpyruvic acid, which forms a green complex when ferric chloride (Fe3+) is added.
The test agar contains DL-phenylalanine and yeast extract.
Incubation is 18 to 24 hours at 35°C.
Positive reaction: appearance of a green color after addition of 10% ferric chloride
Cause of a false positive reaction:
(1) mixed culture
Cause of a false negative reaction:
(1) reading too early
(2) problem with the culture media
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Specialty: Clinical Laboratory, Infectious Diseases
