Urea Agar

Urea Agar was developed by Christensen in 1946 for the differentiation of enteric bacilli, as an improvement over the broth method used at the time1. Urea Agar is recommended for use in the detection of urea hydrolysis in gram-negative organisms and is used to differentiate between rapidly urea hydrolyzing i.e. rapidly positive Proteus species and slower urea hydrolyzing, i.e. slower urea positive members of the Enterobacteriaceae. This medium may also be used in the detection of urease activity in other gram-negative organisms, such as Pseudomonas, Pasteurella, and Brucella2. Webb, et al demonstrated that Urea Agar is useful in differentiating Cryptococcus from other yeast species3.

Organisms capable of hydrolyzing urea form ammonia turning color of the medium phenol red indicator from pale yellow to pink-red in color due to the presence of in the medium. The reduced buffer content and peptone in this medium promote more rapid growth and reaction time for many members of the Enterobacteriaceae. Dextrose is included in the formulation to stimulate urease activity in organisms that hydrolyze urea slowly, and to exclude false-negative reactions. Proteus species rapidly hydrolyze urea, and a positive reaction is usually seen within one to six hours. Other organisms perform this reaction slower, and may require a 24 to 48 hour, or longer, incubation time.

Product NameCatalog #Quantity
Urea Agar mono plate, 90 x 15 mm CU9550P 10/pk
Urea Slant CU9550S 10/pk
Urea Broth CU9550B 10/pk
Urea Indole Motility Agar mono plate, 90 x 15 mm CU9555P 10/pk
Urea Indole Motility Agar Slant CU9555S 10/pk

Quality Control

The following organisms are routinely used for testing for this medium.
Test OrganismsResults
Proteus mirabilis ATCC® 12453 Growth; pink color change
Escherichia coli ATCC® 25922 Growth inhibited, yellow color

User Quality Control

Check for signs of contamination and deterioration. Users of commercially prepared media may be required to perform quality control testing with at least one known organism to demonstrate growth or a positive reaction; and at least one organism to demonstrate inhibition or a negative reaction (where applicable).

Ingredients g/L

(Final pH 6.7 +/- 0.2 at 25°C)
Urea 20.0
Sodium Chloride 5.0
Monopotassium Phosphate 2.0
Peptone 1.0
Dextrose 1.0
Phenol Red 0.012
Agar 15.0
3 total citations

  1. Christensen, W.B. J. Bacteriol.; 52:461.
  2. King, E.O. 1960. The Identification of Unusual Pathogenic Gram Negative Bacteria, U.S.D.H.E.W., CDC, Atlanta, GA.
  3. Webb, C.D., et al. 1973. Identification of Yeasts, U.S.D.H.E.W., CDC, Atlanta, GA.
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