Phenylalanine Slant 4mL Screw Cap Tube, 10/Pk

Phenylalanine Agar (also known as Phenylalanine Deaminase Agar) is a differential medium used to test for the presence of the enzyme phenylalanine deaminase. This test is a critical step in the identification of Gram-negative enteric bacilli, specifically for distinguishing the Proteus, Morganella, and Providencia genera from other members of the Enterobacteriaceae family.

The Test Principle:

The medium contains the amino acid Phenylalanine. If the organism produces the deaminase enzyme, it will remove the amine group ($NH_2$) from the phenylalanine, converting it into phenylpyruvic acid.

The Reagent & Reaction:

Unlike media that contain pH indicators, this test requires the addition of a reagent after incubation to read the result.

1. Inoculation: Streak the slant heavily and incubate overnight.

2. Add Reagent: Add 3-5 drops of 10% Ferric Chloride ($FeCl_3$) solution (sold separately) allowing it to run down the slant over the growth.

3. Positive Result: If phenylpyruvic acid is present, it reacts with the ferric chloride to produce a distinct Dark Green color on the slant within 1-5 minutes.

4. Negative Result: The medium retains its original straw/yellow color.

Key Diagnostic Utility:

This test is the primary method for separating the "Proteus Tribe" (Positive) from E. coli, Salmonella, and Shigella (which are almost always Phenylalanine Deaminase Negative).

• Enzyme Detection: specifically tests for Phenylalanine Deaminase activity.

• Differentiation: Separates Proteus, Providencia, and Morganella (Positive) from other Enterics.

• Rapid Readout: Color change occurs almost immediately after adding the reagent.

• Slant Format: Provides a large surface area for bacterial growth and clear visualization of the green reaction.

• Format: Sterile 4mL agar slants in screw-cap tubes in a 10-pack.

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