CRITERION™ Simmons Citrate Agar

Cat. no. C6950 CRITERION™ Simmons Citrate Agar 47.4gm
Cat. no. C6951 CRITERION™ Simmons Citrate Agar 500gm
Cat. no. C6952 CRITERION™ Simmons Citrate Agar 2kg
Cat. no. C6953 CRITERION™ Simmons Citrate Agar 10kg
Cat. no. C6954 CRITERION™ Simmons Citrate Agar 50kg


Hardy Diagnostics CRITERION™ Simmons Citrate Agar is recommended for use in the differentiation of gram-negative enteric bacilli based on citrate utilization.

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 the early 1920s, Koser developed a liquid medium formulation for the differentiation of fecal coliforms from the coliform group.(5) Simmons later modified this formulation to produce a solid medium that eliminated potential errors when interpreting growth.(9)

CRITERION™ Simmons Citrate Agar contains ammonium dihydrogen phosphate, which supplies the only source of nitrogen, and sodium citrate, which serves as the sole source of carbon. Organisms capable of utilizing ammonium dihydrogen phosphate and citrate will grow unrestricted on this medium. Bromothymol blue acts as a pH indicator, causing the medium to change from green (neutral) to blue (alkaline) with increasing pH. Citrate utilization produces an alkaline carbonate, resulting in a deep blue color change within the agar. The medium will remain green if organisms are not able to metabolize sodium citrate.


Gram weight per liter: 23.7gm/L
Sodium Chloride 5.0gm
Sodium Citrate 2.0gm
Ammonium Dihydrogen Phosphate 1.0gm
Dipotassium Phosphate 1.0gm
Magnesium Sulfate 0.2gm
Bromothymol Blue 0.08gm
Agar 15.0gm

Final pH 6.9 +/- 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 yellow with a light green tinge.

Store the prepared culture media at 2-8ºC.



1. Suspend 23.7gm of the dehydrated culture media in one liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat to boiling to dissolve completely.

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

4. Cool to 45-50ºC.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. L80.


Failure to incubate tubes with loose caps may result in false-negative results.

Use a light inoculum to streak the slant; a heavy inoculum may result in false-positive results.

When inoculating multiple biochemicals from the same culture, inoculate this medium first, or flame inoculating needle prior to streaking this medium. Carryover of glucose or other nutrients onto this medium may result in false-positive results.


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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Salmonella enterica
ATCC ® 14028
E 24-48hr 35°C Aerobic Growth; deep blue color in medium
Klebsiella pneumoniae
ATCC ® 13883
E 24-48hr 35°C Aerobic Growth; deep blue color in medium
Escherichia coli
ATCC ® 25922
E 24-48hr 35°C Aerobic Inhibited; no color change to blue

User Quality Control

Physical Appearance

CRITERION™ Simmons Citrate Agar powder should appear homogeneous, free-flowing, and yellow with a light green tinge in color. The prepared medium should appear slightly opalescent, and dark green 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. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

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

5. Koser, S.A. 1923. Utilization of the salts of organic acids by the colon-aerogenes group. J. Bacteriol., 8:493.

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.

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