Cat. no. C8090 CRITERION™ Modified EC Medium Base 73.2gm
Cat. no. C8091 CRITERION™ Modified EC Medium Base 500gm
Cat. no. C8092 CRITERION™ Modified EC Medium Base 2kg
Cat. no. C8093 CRITERION™ Modified EC Medium Base 10kg
Cat. no. C8094 CRITERION™ Modified EC Medium Base 50kg


Hardy Diagnostics CRITERION™ Modified EC Medium Base, used in conjunction with Novobiocin Supplement (Cat. no. SR181E), is recommended for the selective enrichment of Escherichia coli O157:H7 from meat and poultry products.

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.


Modified EC Medium, supplemented with novobiocin, is based on the modified EC broth formula (mEC+n) described by Okrend and Rose.(8) In this modification, Okrend and Rose reduced the amount of bile salts no. 3 from 1.5 grams to 1.12 grams per liter and added 20 milligrams per liter of sodium novobiocin. When using this formulation, Okrend et. al. reported that mEC+n was helpful in the enrichment and detection of E. coli O157:H7 from meat and poultry products. Consequently, this formulation is currently recommended by the U.S.D.A for testing food products.(9-11)

Hardy Diagnostics Modified EC Medium Base includes peptone which provides nitrogen, vitamins and amino acids to the medium. Lactose is added as a carbon source for microorganisms that can ferment sugar like E. coli. Bile salts are used as a selective agent to inhibit certain gram-positive cocci and spore-forming bacteria. Buffers in the form of dipotassium phosphate and monopotassium phosphate promote the recovery of injured or damaged cells. Sodium chloride provides a suitable ionic environment to promote growth. In addition, novobiocin supplement, when added, suppresses the growth of nuisance microorganisms commonly found in food products.

The selectivity of this medium is based on the addition of bile salts no. 3 and by the further addition of novobiocin supplement to the completed medium. Both of these agents work to suppress the growth of competing microorganisms commonly found in food products. Novobiocin supplement (Cat. no. SR181E) may be purchased in a freeze-dried state that can be rehydrated with sterile purified water prior to supplementation.


Gram weight per liter: 36.6gm/L
Casein Peptone 20.0gm
Bile Salts No. 3 1.12gm
Lactose 5.0gm
Dipotassium Phosphate 4.0gm
Monopotassium Phosphate 1.5gm
Sodium Chloride 5.0gm

Final pH 6.9 +/- 0.2 at 25ºC.

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

Novobiocin Supplement
Composition per 10.0ml
Novobiocin Supplement 20.0mg


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 culture media at 2-30ºC.



Modified EC Medium:

1. Suspend 36.6gm of the dehydrated culture media in 1 liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat as necessary to dissolve completely.

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

4. Cool media to room temperature.

5. Aseptically add 10ml of rehydrated Novobiocin supplement (Cat. no. SR181E) and mix well.

Novobiocin Supplement:

1. Aseptically add 10ml of sterile purified water to vial.

2. Shake to dissolve contents.


For information on procedures and interpretation of results, consult listed references.


Standard microbiological supplies and equipment such as autoclaves, incinerators, incubators, Novobiocin supplement (Cat. no. SR181E), MacConkey Sorbitol Agar plates (Cat. no. G36), and Butterfield's Phosphate Buffer (Cat. no. U290), etc., are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli O157:H7
ATCC ® 35150
A 24hr 35°C Aerobic Growth; turbidity with gas production (gas bubble in durham tube)
Enterococcs faecalis
ATCC ® 29212
B 24hr 35°C Aerobic Inhibited

User Quality Control

Physical Appearance

CRITERION™ Modified EC Medium Base powder should appear homogeneous, free-flowing, and light beige in color. The prepared media should appear clear and light amber in color.


1. Standard Methods for the Examination of Water and Wastewater , 20th ed. 1998. American Public Health Association, Washington, D.C.

2. Compendium of Methods for the Microbiological Examination of Foods, 4th ed. 2001. American Public Health Association, Washington, D.C.

3. Standard Methods for the Examination of Dairy Products, 16th ed. 1992. American Public Health Association, Washington, D.C.

4. Bacteriological Analytical Manual (BAM), 2002. Association of Official Analytical Chemists International, Gaithersburg, MD.

5. Official Methods of Analysis of the Association of Official Analytical Chemists, 15th ed. 1990. AOAC, Arlington, VA.

6. Hajna A.A., and C.A. Perry. 1943. Comparative study of presumptive and confirmatory media for bacteria of the coliform group and for fecal streptococci. Am. J. Public Health. 33:550-556.

7. Perry, C.A. and Hajna, A.A. 1944. Further evaluation of EC medium for the isolation of coliform bacteria and Escherichia coli. Am. J. Public Health and Nation's Health. 34:735-748.

8. Okrend, A.J.G., and B.E. Rose. 1989. USDA Communication No. 38, rev. 4. USDA, Washington, D. C.

9. Okrend, A.J.G., B.E. Rose and B. Bennet. 1990. A screening method for the isolation of Escherichia coliO157:H7 from ground beef. J. Food Prot. 53:249-252.

10. Okrend, A.J.G., B.E. Rose and C.P. Latuada. 1990. Use of 5-bromo-4-chloro-3-indoxyl-b-D-glucuronide in MacConkey sorbitol agar to aid in the isolation of Escherichia coli O157:H7 from ground beef. J. Food Prot. 53:941-943.

11. Okrend, A.J.G., B.E. Rose and Matner, R. 1990. An improved screening method for the detection and isolation of Escherichia coli O157:H7 from meat, incorporating the 3M Petrifilm test kit- HEC- for hemorrhagic Escherichia coli O157:H7. J. Food. Prot. 53:936-940.

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