The ability of Proteus species to be able to deaminate phenylalanine to phenylpyruvic acid using the enzyme
Phenylalanine ammonia-lyase (pal enzyme) is an important and useful reaction in the differentiation of members of the family of Enterobacteriaceae.This biochemical tests for identification of bacteria is used for the differentiation of Proteus and Providencia group of organisms from other members of Enterobacteriaceae on the basis of their ability to form phenyl pyruvic acid from phenylalanine
Principle of Phenylalanine Agar
- The yeast extract in the medium supports the growth of the organisms.
- Sodium chloride maintains osmotic equilibrium.
- The phenylalanine serves as the substrate for enzymes, which are able to deaminate it in order to form phenylpyruvic acid.
Composition of Phenylalanine Agar slant
The following ingredients are used for the composition Phenylalanine agar slant
|Ingredients||Grams / Litre|
|Final pH at temperature 25°C||7.3±0.2|
How to Prepare Phenylalanine Agar slant
- Start by suspending 26 grams in 1000 ml distilled water.
- Heat to boiling in order to dissolve the medium completely.
- Dispense in tubes and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
- Allow the tubed medium to cool in a slanting position.
Appearance of Medium after preparation
It’s appear Light amber coloured slightly opalescent gel forms in tubes as slants
phenylalanine deaminase test reagent
- 10% ferric chloride solution
- 0.1N HCl
Phenylalanine Test Procedure
- inoculate the slant surface with plenty of inoculum then incubate it for 12-16 hours
- After incubation, now add 0.2 ml or 5 drops of 10% ferric chloride solution and 5 drops of 0.1N HCl so that the solution floods all over the growth.
- Gently shake the tube and observe for color change
- In a positive reaction, any phenylpyruvic acid present will react with the ferric salt in the reagent to give a green color
phenylalanine deaminase test results and interpretation
Interpretation of the results is done within 5 minutes upon addition of reagent as the green colour fades quickly
|Positive||green color develops within five minutes after addition of reagents|
|Negative||no color change (negative reaction)|
Culture observation and Phenylalanine deamination
|Escherichia coli||Negative : no change after addition of 10% Ferric chloride|
|Enterobacter aerogenes||Negative : no change after addition of 10% Ferric chloride|
|Proteus vulgaris||Positive : green colouration after addition of 10% Ferric chloride|
|Proteus mirabilis||Positive : green colouration after addition of 10% Ferric chloride.|
phenylalanine deaminase test positive bacteria
- Providencia alcalifaciens
- Proteus vulgaris
- Proteus mirabilis
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