Cat. no. C6500 CRITERION™ OF Basal Medium 18.8gm
Cat. no. C6501 CRITERION™ OF Basal Medium 500gm
Cat. no. C6502 CRITERION™ OF Basal Medium 2kg
Cat. no. C6503 CRITERION™ OF Basal Medium 10kg
Cat. no. C6504 CRITERION™ OF Basal Medium 50kg


Hardy Diagnostics CRITERION™ OF Basal Medium is used with added carbohydrates for the differentiation of gram-negative bacteria based on oxidation-fermentation patterns.

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.


OF Basal Medium was developed by Hugh and Leifson to aid in the identification of gram-negative bacteria on the basis of their ability to oxidize or ferment a specific carbohydrate.(6)

As compared to other OF Media, Hugh and Leifson's formula employs a low peptone/carbohydrate ratio and a minimal amount of agar. The decreased amount of peptone reduces the formation of alkaline amines which can ultimately mask the small quantities of acid that may be produced from oxidative metabolism.(5) The increased carbohydrate results in an increase in the amount of acid that may be formed. The small amount of agar added to the medium provides a semi-solid structure which concentrates the acid at the point of reaction, thereby facilitating visual interpretation of the pH shift.

Proper performance of the OF test requires an organism to be inoculated to two tubes of each OF Medium. Once inoculated, one tube is overlaid with mineral oil or melted paraffin. The other tube is left open to the air.

Oxidative utilization of the carbohydrate will result in acid production (yellow) in the open tube only. Fermentative utilization of the carbohydrate will result in acid production (yellow) in both the open and closed tubes. Acidic changes in the overlaid tubes are considered to be a result of true fermentation, while acidic development in the open tubes are due to oxidative utilization of the carbohydrate present. Asaccharolytic organisms will not produce acid in either tube.


Gram weight per liter: 9.4gm/L
Sodium Chloride 5.0gm
Pancreatic Digest of Casein 2.0gm
Dipotassium Phosphate 0.3gm
Bromothymol Blue 0.08gm
Agar 2.0gm

OF Media with carbohydrates require an addition of 10.0gm of specific carbohydrate.

Final pH 6.8 +/- 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 beige with a greenish tinge.

Store the prepared culture media at 2-8ºC.



1. Combine 9.4gm of medium with one liter of deionized water. Stir to mix thoroughly.

2. Boil to dissolve completely. Do not overheat.

3. Autoclave at 121ºC. for 15 minutes.

4. Add 1% carbohydrate before or after sterilization, depending on heat lability.

5. Dispense into test tubes.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. Y51.


Organisms that only oxidize dextrose will not ferment any other carbohydrate. Other carbohydrates will only be oxidized. The overlaid (closed) tube, therefore, may be omitted when determining other carbohydrate utilization of such organisms.

Some microorganisms do not grow in OF Basal Medium. It may be necessary to use another basal medium containing dextrose to confirm the negative reaction.

Some mineral oils are acidic and may result in erroneous results.


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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
OF Base Medium:
Escherichia coli
ATCC ® 25922
D 18-48hr 35°C Aerobic Growth; no color change (top may turn blue at 48 hours) in open tube and in oil overlaid tube
OF Dextrose:
Escherichia coli
ATCC ® 25922
D 18-24hr 35°C Aerobic Growth; acid (yellow) reaction and gas in open tube and in oil overlaid tube
Shigella flexneri
ATCC ® 12022
D 18-24hr 35°C Aerobic Growth; acid (yellow) reaction in open tube and in oil overlaid tube
Pseudomonas aeruginosa
ATCC ® 27853
D 18-24hr 35°C Aerobic Growth; acid (yellow) reaction in open tube; no change in oil overlaid tube

User Quality Control


CRITERION™ OF Basal Medium powder should appear homogeneous, free-flowing, and light beige with a greenish tinge in color. The prepared media should appear slightly opalescent, and 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. 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. Hugh, R. and Leifson, E. 1953. J. Bacteriol.; 66:24-26.

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