CRITERION™ Phenylalanine Agar

Cat. no. C6600 CRITERION™ Phenylalanine Agar 46gm
Cat. no. C6601 CRITERION™ Phenylalanine Agar 500gm
Cat. no. C6602 CRITERION™ Phenylalanine Agar 2kg
Cat. no. C6603 CRITERION™ Phenylalanine Agar 10kg
Cat. no. C6604 CRITERION™ Phenylalanine Agar 50kg


Hardy Diagnostics CRITERION™ Phenylalanine Agar is recommended for use in the differentiation of gram-negative enteric bacilli based on the ability of microorganisms to produce phenylpyruvic acid by oxidative deamination.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.


In 1950, Hendriksen demonstrated that Proteus spp. were able to convert the amino acid phenylalanine to phenylpyruvic acid. Later, Buttiaux et al. developed a culture medium for detecting the formation of Proteus, Providencia, and Morganella groups.(1) This medium was modified by Bynae and further modified by Ewing et al. who simplified Bynae's formula by omitting proteose peptone.(2,3) Hardy Diagnostics CRITERION™ Phenylalanine Agar follows the formulation established by Ewing.

The deamination of phenylalanine by oxidative enzymes results in the formation of phenylpyruvic acid. After incubation, an aqueous solution of ferric chloride is added. If phenylpyruvic acid is present, a light to deep green color is produced. Of the Enterobacteriaceae, only Proteus, Providencia, and Morganella species possess enzymes capable of deaminating phenylalanine.(4)


Gram weight per liter: 23.0gm/L
Sodium Chloride 5.0gm
Yeast Extract 3.0gm
Phenylalanine 2.0gm
Dipotassium Phosphate 1.0gm
Agar 12.0gm

Final pH 7.3 +/- 0.2 at 25ºCC.

* Adjusted and/or supplemented as required to meet performance criteria.


Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original light tan.

Store the prepared culture media at 15-30ºC.



1. Suspend 23gm of the dehydrated culture media in one liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat to boiling to dissolve completely. Do not overheat.

3. Pour desired volume into tubes and sterilize in the autoclave at 121ºC. for 15 minutes.

4. Slant tubes after autoclaving.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. L21.


The green color reaction of a positive test fades rapidly. Test results must be interpreted within 5 minutes following the application of ferric chloride or false-negative results may occur.

Slight agitation of the medium flooded with ferric chloride will dislodge surface colonies and produce a faster more pronounced color reaction.


Standard microbiological supplies and equipment such as autoclaves, incinerators, ferric chloride reagent (Cat. no. Z63), other culture media, and incubators, etc., are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Proteus mirabilis
ATCC ® 12453**
A 18-24hr 35°C Aerobic Growth; turns green after the addition of 4-5 drops of ferric chloride with agitation, may take 1-5 minutes
Escherichia coli
ATCC ® 25922**
A 18-24hr 35°C Aerobic Growth; ferric chloride remains yellow

** Recommended QC strains for User Quality Control according to the CLSI document M22 when applicable.

User Quality Control

Physical Appearance

CRITERION™ Phenylalanine Agar powder should appear homogeneous, free-flowing, and light tan in color. The prepared medium should appear slightly opalescent, and light amber in color.


1. Buttiaux, et al. 1954. Ann. Inst. Pasteur; 87:375-386.

2. Ewing, et al. 1957. Pub Hlth Lab.; 15:153.

3. Hendriksen. 1950. J. Bacteriol.; 60:225.

4. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.

5. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

6. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

7. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

8. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

ATCC is a registered trademark of the American Type Culture Collection.