Phenylalanine deaminase test principle, procedure, and purpose

The phenylalanine deaminase test is important to differentiate proteus and providendia from other enterobacteria and enterocolitis.

Principle of phenylalanine deaminase test

Some enterobacteria members can form phenyl pyruvic acid from phenylalanine by oxidative deamination.

When this phenylalanine reacts with acidified ammonium sulfate OR 10 % ferric chloride solution to form phenyl pyruvic acid.This phenyl pyruvic acid gives green color.

Phenylalanine deaminase test reagents

Following are the p. alanine test reagents

How to prepare phenylalanine Agar?

• Yeast extract – 3 g
• DL-phenylalanine – 2 g
• Disodium Phosphate – 1 g
• Sodium Chloride – 5 g
• Agar – 12 g
• Distilled water – 1 litter

Dispense into the tube while hot, after autoclaving. Allow hardening in slant.

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Phenylalanine deaminase test procedure

Following is the procedure

• Inoculate a slop of phenylalanine agar with test organisms and incubate overnight.at 35 – 37 C.
• Add 4 to 5 drops of freshly prepared ferric chloride to the tube.
• Allow the reagents to run down the slope.
• Look for color change on the slope, it will turn in 5 minutes.
• The GREEN color is the sign of a positive test.

Positive Control : Proteus Vulgaris

Negative Control : E.coli