Cat. no. C7230 CRITERION™ Urea Agar Base Concentrate 54gm
Cat. no. C7231 CRITERION™ Urea Agar Base Concentrate 500gm
Cat. no. C7232 CRITERION™ Urea Agar Base Concentrate 2kg
Cat. no. C7233 CRITERION™ Urea Agar Base Concentrate 10kg


Hardy Diagnostics CRITERION™ Urea Agar Base Concentrate is recommended for use in the detection of urea hydrolysis in gram-negative organisms.

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.


Urea Agar was developed by Christensen in 1946 for the differentiation of enteric bacilli, as an improvement over the broth method used at that time.(3) Urea Agar is used to differentiate between rapidly positive Proteus species and other slower urea positive members of the Enterobacteriaceae. This medium may also be used in the detection of ureaseactivity in other gram-negative organisms, such as Pseudomonas, Pasteurella, and Brucella.(5) Webb et al. also reported that Urea Agar is useful in differentiating Cryptococcus from other yeast species.(9)

CRITERION™ Urea Agar Base Concentrate contains urea as a source of nitrogen for the production of urease and phenol red as the pH indicator. Organisms capable of hydrolyzing urea form ammonia as a by product, thus turning the medium alkaline. The pH indicator turns from pale yellow to pink-red in color under these conditions. The reduced buffer content and peptone in this medium promote rapid growth and a faster 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-negativereactions. Proteus species rapidly hydrolyze urea and a positive reaction is usually seen within one to six hours. Other organisms may require a 24 to 48 hour, or longer, incubation time.

CRITERION™ Urea Agar Base Concentrate is a 10X concentrate for the preparation of Christiansen's medium and requires the supplementation of bacteriological grade agar (Cat. no. C5000) for the preparation of solid media.


Gram weight per liter: 29.0gm/L
Urea 20.0gm
Sodium Chloride 5.0gm
Gelatin Peptone 1.0gm
Dextrose 1.0gm
Disodium Phosphate 0.1gm
Monopotassium Phosphate 0.09gm
Phenol Red 0.012gm

Final pH 6.8 +/- 0.2 at 25ºC.

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

Composition per liter:
Agar, Bacteriological Grade 15.0gm/L


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 orange or light pink.

Store the prepared culture media at 2-8ºC.



1. Suspend 29gm of the Urea Agar Base Concentrate dehydrated culture media in 100ml of distilled or deionized water. Stir to mix thoroughly. Sterilize by filtration using a 0.2 micron filter.

2. Suspend 15gm of bacteriological grade agar (Cat. no. C5000) in 900ml of distilled or deionized water.

3. Sterilize the agar solution in the autoclave at 121ºC. for 15 minutes.

4. Cool the agar solution to 45 to 50ºC and aseptically add 100ml of the sterile Urea Agar Base Concentrate.

5. Mix thoroughly and dispense aseptically into sterile tubes.

6. Cool tubed medium in a slanted position so deep butts are formed.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. L65.


To facilitate growth and the urea hydrolysis reaction, do not use inoculum from a broth suspension.

Due to nutritional variation, some strains may grow poorly or fail to grow on this medium.

Urea Agar relies upon the pH indicator to detect an alkaline reaction such as the hydrolysis of urea. After prolonged incubation times, a false-positive alkaline reaction may be seen due to the hydrolysis of peptones and the release of amino acid residues. To rule out this occurrence, check the test with a control (an uninoculated tube of Urea Agar along with the inoculated tube) during prolonged incubation.

To detect Proteus species, the Urea Agar slants may be examined within six hours of inoculation.

Urea Agar should not be used to determine the quantitative rate of urease activity, as organisms vary in their capability and rate of hydrolysis.

Failure to incubate this medium with loose caps may cause erroneous results.

Do not heat the Urea Agar slants, as urea decomposes very readily when heated.


Standard microbiological supplies and equipment such as autoclaves, innoculation loops, incinerators, and incubators, etc., are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Proteus mirabilis
ATCC ® 12453
E 18-24hr 35°C Aerobic Positive: Growth; pink color change
Escherichia coli
ATCC ® 25922
E 18-24hr 35°C Aerobic Negative: Growth; yellow color or no color change

User Quality Control

Physical Appearance

CRITERION™ Urea Agar Base Concentrate powder should appear homogeneous, free-flowing, and light orange to light pink in color. The prepared medium should appear opalescent, and light to medium yellow-orange in color.


1. 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.

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

3. Christensen, W.B. 1946. Urea decomposition as a means of differentiating Proteus and paracolon cultures from each other and from Salmonella and Shigella types. J. Bacteriol. 52:461.

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

5. King, E.O. 1960. The Identification of Unusual Pathogenic Gram Negative Bacteria, U.S.D.H.E.W., CDC, Atlanta, GA.

6. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria, Vol. I. Williams & Wilkins, Baltimore, MD.

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

8. Quality Assurance for Commercially Prepared Microbiological Culture Media, M22. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS), Wayne, PA.

9. Webb, C.D., et al. 1973. Identification of Yeasts, U.S.D.H.E.W., CDC, Atlanta, GA.

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