Cat. no. G122 Casein Agar, 15x100mm Plate, 18ml 10 plates/bag


Hardy Diagnostics Casein Agar is recommended for use as a medium for the differentiation of aerobic actinomycetes based on casein proteolysis. Organisms that can hydrolyse casein, such as Streptomyces , Pseudomonas , and Actinomadura spp. will produce a clear halo in the surrounding medium.


Casein Agar is a growth medium used for the detection of hydrolytic microorganisms. Proteins are made up of various chains of amino acids linked together by peptide bonds, and hydrolytic microorganisms have the ability to cleave peptide bonds. Casein Agar consists of agar supplemented with skim milk as the casein source. Clearing occurs around the colonies that hydrolyze casein. This medium is not recommended for the use as a general purpose medium as it supports the growth of a wide variety of organisms.


Ingredients per liter of deionized water:*

Dry Milk, Instant Nonfat 50.0gm
Pancreatic Digest of Casein 5.0gm
Yeast Extract 2.5gm
Glucose 1.0gm
Agar 12.5gm

Final pH 6.8 +/- 0.3 at 25ºC.

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


Storage: Upon receipt store at 2-8ºC. away from direct light. Media should not be used if there are any signs deterioration (shrinking, cracking, or discoloration), contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.



Specimen Collection: Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport media and refrigerated until inoculation. Consult listed references for information on specimen collection. (1-7)

Select a colony and prepare a Gram-stained smear of the isolate and examine to confirm that the morphology is appropriate for the selected organism.

Directly inoculate Casein Agar by streaking a single line of the isolate to be tested onto the agar surface with a sterile inoculating loop.

Incubate the media at 35ºC.

Casein Agar may need to be incubated for up to three weeks to allow positive hydrolytic reactions to develop. Examine plates at regular intervals for colony growth and hydrolytic reactions for the first 48-72 hours and periodically thereafter.

Decomposition of casein may be detected by observing clear zones in the white, opaque skim milk around the inoculum. Growth without clearing around the inoculum is considered a negative test result.


Positive Test - Clearing is observed around and/or beneath colony growth (hydrolysis).

Negative Test - No clearing is observed around and/or beneath the inoculum.

A positive reaction is indicated by a clearing in the media surrounding the colonies. Pseudomonas aeruginosa will hydrolyze casein and may produce a yellow to green diffusible pigment. (7)



Standard microbiological supplies and equipment such as loops, swabs, applicator sticks, other culture media, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Pseudomonas aeruginosa
ATCC ® 27853**
* 24-48hr 35°C Aerobic Growth; clear zones surrounding colonies, colonies may have greenish pigment
Escherichia coli
ATCC ® 25922**
* 24-48hr 35°C Aerobic Growth; no clear zones

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


Physical Appearance

Casein Agar should appear opaque, with a precipitate, and white to off-white in color.

P. aeruginosa growing on Casein Agar

Pseudomonas aeruginosa (ATCC ® 27853) growing on Casein Agar (Cat. no. G122). Incubated aerobically for 24 hours at 35ºC.

E. coli growing on Casein Agar

Escherichia coli (ATCC ® 25922) growing on Casein Agar (Cat. no. G122). Incubated aerobically for 24 hours at 35ºC.


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

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

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

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

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

7. Eaton, A.D., Clesceri, L.S. and Greenberg, A.E. 1995. Standard Methods for the Examination of Water and Wastewater , 19th ed. APHA, Washington, D.C.

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