Cat. no. C6720 CRITERION™ R2A Agar 30.4gm
Cat. no. C6721 CRITERION™ R2A Agar 500gm
Cat. no. C6722 CRITERION™ R2A Agar 2kg
Cat. no. C6723 CRITERION™ R2A Agar 10kg
Cat. no. C6724 CRITERION™ R2A Agar 50kg


Hardy Diagnostics CRITERION™ R2A Agar is recommended for use in the pour plate and spread plate methods for enumeration of heterotrophic bacteria in water, especially potable water.

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.


Reasoner and Geldreich, of the U.S. Environmental Protection Agency, developed R2A Agar for the recovery and isolation of aerobic and facultative anaerobic heterotrophic bacteria from treated potable water.(1,2)

R2A Agar, as compared to other media recommended for the heterotrophic plate count (HPC), contains reduced levels of peptone, yeast extract, and dextrose. The decreased nutrient level, along with the addition of sodium pyruvate, enhances the recovery of many stressed and chlorine-tolerant bacteria that are present in treated waters.(2) Also, the heterotrophic bacteria recovery method using R2A Agar requires incubation temperatures below routine laboratory requirements, which further enhances the recovery of many bacteria.(4,5)

This formula contains peptones that provide nitrogen, vitamins, amino acids, and minerals. Dextrose acts as a carbon source, while yeast extract is added for trace elements and vitamins. For the recovery of injured cells, soluble starch and sodium pyruvate are used to neutralize toxins. Magnesium sulfate provides magnesium cations and sulfate. Potassium phosphate buffers the pH of the media and agar is used for solidification.


Gram weight per liter: 15.2gm/L
Casein Acid Hydrolysate 0.5gm
Yeast Extract 0.5gm
Dextrose 0.5gm
Soluble Starch 0.5gm
Dipotassium Phosphate 0.3gm
Sodium Pyruvate 0.3gm
Casein Peptone 0.25gm
Peptic Digest of Animal Tissue 0.25gm
Magnesium Sulfate 0.05gm
Agar 15.0gm

Final pH 7.2 +/- 0.2 at 25ºC.

* 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 beige.

Store the prepared plated culture media at 2-8ºC.
Store the prepared tubed and bottled culture media at 2-30ºC.



1. Suspend 15.2gm of the dehydrated culture media in 1 liter of distilled or deionized water. Stir to mix thoroughly.

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

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

4. Cool to 45-50ºC. and dispense.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G54.


The pour plate method is not highly recommended because the recovery of injured bacteria may be lessened by the heat of the media at 45ºC. For small sample volumes, the spread plate technique is most effective. When larger amounts of water need to be tested, the membrane filter method is suggested.


Standard microbiological supplies and equipment such as autoclaves, petri dishes, membrane filters, incinerators, and incubators, etc., are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli
ATCC® 8739
J 1-3 days 35°C Aerobic Growth
Enterococcus faecalis
ATCC® 29212
J 1-3 days 35°C Aerobic Growth
Staphylococcus aureus
ATCC® 6538
J 1-3 days 35°C Aerobic Growth
Aspergillus brasiliensis
formerly A. niger
ATCC® 16404
J 1-5 days 30°C Aerobic Growth
Candida albicans
ATCC® 10231
J 1-5 days 30°C Aerobic Growth
Bacillus subtilis
ATCC® 6633
J 1-3 days 35°C Aerobic Growth

User Quality Control

Physical Appearance

CRITERION™ R2A Agar powder should appear homogeneous, free-flowing, and light beige in color. The prepared media should appear clear, slightly opalescent, and light amber in color.


1. Reasoner, D.J., and Geldreich, E.E. 1979. Paper No. N7, Annual Meeting of The American Society for Microbiology.

2. Reasoner, D.J., and Geldreich, E.E. 1985. Applied and Environmental Microbiology; 49:1-7.

3. Standard Methods for the Examination of Water and Wastewater. 1995. 19th ed. American Public Health Association, Washington, D.C.

4. Stark and McCoy. 1938. Zentralbl. Bakteriol. Parasitenkd. Infektionskr. Hyg., Abt. 2; 98:201.

5. Collins and Willoughby. 1962. Arch. Mikrobiol.; 43:294.

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