M-Green Yeast and Mold Agar

Casein and gelatin peptones provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Dextrose is the fermentable carbohydrate providing carbon and energy. Bacteriological agar is the solidifying agent. Potassium phosphate is a buffering agent. Magnesium sulfate, thiamine, and diastase (a mixture containing amylolytic (starch) enzymes) provide essential ions, minerals, and nutrients. Bromocresol green is the pH indicator, facilitating visualization and counting of fungal colonies. The colonies are green due to diffusion of bromocresol green into the colonies. The end products of the microbial growth diffuse into the medium, reducing the pH and turning the indicator to yellow. Bacterial growth is inhibited by an acid pH.

Yeasts are large green opaque colonies. Moulds appear green and filamentous. Bacteria able to grow at this pH form smaller clear to white colonies.

Preparation

Suspend 88.2 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. AVOID OVERHEATING. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 10 minutes.

Instructions for use

Filter-membrane technique:

1. Filter an appropriate volume of sample through a 0.45 µm membrane.
2. Place the membrane onto the surface of an agar plate, avoiding the formation of air bubbles.
3. Invert the plates and incubate at 25-30 °C for 48-72 hours.

• Jong, S.S. and M.J. Edwards, 1991, American Type Culture Collection Catalog of filamentous fungi, 18th ed. American Type Culture Collection, Rockville, MD.
• Thom and Raper, Manual of the Aspergilli 39:1945
• Smith G. An Introduction to Industrial Mycology 5th Ed. Arnold LR London, 1960.