Cat. no. C7400 CRITERION™ MYP Agar Base 89gm
Cat. no. C7401 CRITERION™ MYP Agar Base 500gm
Cat. no. C7402 CRITERION™ MYP Agar Base 2kg
Cat. no. C7403 CRITERION™ MYP Agar Base 10kg
Cat. no. C7404 CRITERION™ MYP Agar Base 50kg


Hardy Diagnostics' CRITERION™ MYP Agar Base supplemented with egg yolk emulsion and polymyxin B sulfate is recommended for the isolation and identification of Bacillus spp. It is also recommended by the American Public Health Association (APHA) for the isolation and presumptive identification of Bacillus cereus in foods.

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.


Mossel et al., formulated Mannitol Egg Yolk Polymyxin (MYP) Agar to isolate and enumerate Bacillus cereus from foods. This medium can differentiate B. cereus from other types of bacteria present in a sample based on typical biochemical reactions.

B. cereus is commonly found in nature, on vegetables and in some processed foods. Under favorable conditions, the organism can grow to sufficient numbers and cause gastrointestinal illness. Outbreaks of foodborne illness have been associated with the ingestion of boiled and cooked rice, cooked meats, cooked vegetables and a variety of other food types.

B. cereus is the etiological agent in two distinct types of food-poisoning: (1) diarrheal type, characterized by abdominal pain with diarrhea 8 to 16 hours after ingestion of the contaminated food, and (2) the emetic type, characterized by nausea and vomiting 1 to 5 hours after eating the contaminated meal. B. cereus spores can survive normal cooking procedures and when the cooked food is stored improperly, the spores germinate and vegetative cells multiply. As of yet, the toxin or other virulence factor responsible for the different syndromes has not been identified.

Hardy Diagnostics' CRITERION™ MYP Agar Base contains meat extract and peptones that supply nitrogen, vitamins and minerals. Mannitol is the carbohydrate source and phenol red is the pH indicator; thus, bacterial colonies capable of fermenting mannitol will appear yellow. Sodium chloride aids cells in maintaining osmotic equilibrium. When supplemented with polymyxin B and egg yolk emulsion, the medium can be used for the isolation and identification of Bacillus species, particularly B. cereus. Polymyxin B helps restrict the growth of gram-negative microorganisms present in the sample, while egg yolk emulsion helps differentiate lecithinase producing colonies. The insoluble products of egg yolk lecithin accumulate around colonies that produce lecithinase to form a zone of white precipitate.


Gram weight per liter: 46.0gm/L
Peptone 10.0gm
Mannitol 10.0gm
Sodium Chloride 10.0gm
Meat Extract 1.0gm
Phenol Red 0.025gm
Agar 15.0gm

Final pH 7.2+/- 0.1 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 pink.

Store the prepared culture media at 2-8ºC.



1. Suspend 44.5gm of the dehydrated culture media in 1 liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat to boiling for one minute to dissolve completely.

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

4. Cool to 45-50ºC.

5. Aseptically add 25ml of sterile egg yolk emulsion and 0.1ml of polymyxin B and mix thoroughly.

6. Aseptically dispense desired volume into sterile containers.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G147.



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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Bacillus cereus
ATCC® 13061
A 18-48hr 35°C Aerobic Growth; pink to red colonies with zone of whitish precipitate
Bacillus subtilis
ATCC® 6633
A 18-48hr 30-35°C Aerobic Growth; yellow colonies with no zone of precipitate
Pseudomonas aeruginosa
ATCC® 27853
B 18-48hr 30-35°C Aerobic Partial to complete inhibition

User Quality Control

Physical Appearance

CRITERION™ MYP Agar Base powder should appear homogeneous, free-flowing, and pink in color. The prepared media should appear opaque, and orange in color.


1. American Public Health Association. Standard Methods for the Examination of Dairy Products, APHA, Washington, D.C.

2. 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.

3. APHA Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods, APHA, Washington, D.C.

4. Association of Official Analytical Chemists. Official Methods of Analysissm, AOAC, Washington, D.C.

5. Coliner, A.R. 1948. The action of Bacillus cereus and related species on the lecithin complex of egg yolk. J. Bacteriol.; 55:777-785.

6. U.S. Food and Drug Administration. Bacteriological Analytical Manual. AOAC, Arlington, VA.

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