Mannitol Yolk Polymyxin (MYP) Agar

Cat. no. G147 Mannitol Yolk Polymyxin Agar, 15x100mm Plate, 18ml 10 plates/bag


Hardy Diagnostics Mannitol Yolk Polymyxin (MYP) Agar is recommended for the enumeration, detection and isolation of Bacillus cereus in food.

This product is not intended to be used for the diagnosis of human disease.


Bacillus 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 syndromes: (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. Bacillus cereus spores can survive normal cooking processes and when the cooked food is stored improperly, the spores germinate and vegetative cells multiply. The toxin or other virulence factors responsible for the syndromes has not yet been identified.

Mosel et al., formulated Mannitol Egg Yolk Polymyxin Agar to isolate and enumerate Bacillus cereus from foods. MYP Agar contains beef extract, nitrogen, vitamins and minerals. Mannitol is the carbohydrate source. Phenol Red is the pH indicator. Polymyxin inhibits normal microbial flora present in the sample. Bacteria that produce lecithinase hydrolyze the lecithin in the egg yolk. The insoluble products of egg yolk lecithin accumulate around the colonies to form a zone of white precipitate. Bacteria which ferment mannitol produce acid products and will form colonies that are yellow. Bacillus cereus is typically mannitol-negative (pink to red colonies) and lecithinase-positive (zone of precipitate around the colonies).


Ingredients per liter of deionized water:*

Mannitol 10.0gm
Peptone 10.0gm
Sodium Chloride 10.0gm
Meat Extract 1.0gm
Phenol Red 0.025gm
Egg Yolk Emulsion 100.0ml
Polymyxin 25,000U
Agar 14.0gm

Final pH 7.2 +/- 0.2 at 25ºC.

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




1. Inoculate the plates by spreading the sample on the surface of the medium.

2. Incubate for 18-48 hours at 30 +/- 2ºC.

3. Examine for the presence of colonies typical of Bacillus cereus . Colonies will appear rough, dry and pink or purple in color surrounded by a zone of dense white precipitate.

Consult references for detailed procedure. (2-4)


Consult appropriate references. (2-4)



Standard microbiological supplies and equipment such as loops, swabs, applicator sticks, other culture media, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Bacillus cereus
ATCC ® 13061
A 18-48hr 30-35°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 preciptate
Pseudomonas aeruginosa
ATCC ® 27853
B 18-48hr 30-35°C Aerobic Partial to complete inhibition


Physical Appearance

Mannitol Yolk Polymyxin (MYP) Agar should appear slightly opalescent to opaque, and pink-orange to light orange in color.


1. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

2. Association of Official Analytical Chemists. Official Methods of Analysissm, AOAC, 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. U.S. Food and Drug Administration. Bacteriological Analytical Manual . AOAC, Arlington, VA.

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