m-Dixon agar

The species of the genus Malassezia are found in the microbial flora that inhabit the skin of homeothermic animals. Most of the species of this genus are lipid-dependent yeasts that colonize the seborrheic part of the skin and they are described as being associated with Tinea versicolor or seborrheic dermatitis.

Some Malassezia species can produce precipitates in the medium. It is likely that the appearance of precipitates is due to the production of insoluble free fatty acids from lipid sources contained in Dixon Agar. Moreover, it is possible that, as the isolate continues to grow, some of these fatty acid precipitates are used, which would explain the appearance of clear visible areas directly adjacent to the microbial growth. It is known that species of Malassezia have differences in their patterns of lipid use, and it has also been proven that M. sympodialis produces comparatively more insoluble free fatty acids from lipid sources than M. furfur. These observations suggest differences in the systems of lipase enzymes in species of Malassezia.

Casein peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. The malt extract is a source of carbon, proteins and nutrients, also necessary for growth. This medium is adequate for yeasts and molds as it contains a high concentration of maltose and other saccharides as sources of energy. The addition of ox bile inhibits the growth of Gram-positive organisms. The oleic acid and Tween 40 are a source of lipids. The cycloheximide is an antibiotic which inhibits saprophytic fungi, but allows the growth of pathogenic fungi.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 104.8 grams in one liter of distilled water. Mix thoroughly. Heat, shaking it frequently, until boiling and complete dissolution. Sterilize at 121 °C for 15 minutes. Cool down to 45-50 °C and pour into Petri dishes.

Warning: this medium is toxic if ingested, inhaled or if it comes into contact with skin. Use gloves, and eye and face protectors.

Instructions for use

1. Inoculate and incubate at a temperature of 32 °C for 7 days.

• Kindo AJ, Sophia SK, Kalyani J, Anandan S. (Jul-Sep 2004). “Identification of Malassezia species”. Indian J Med Microbiol. 22(3):179-81. PMID: 17642728.
• Kaneko T., Makimura K., Abe M., Shiota R., Nakamura Y., Kano R., Hasegawa A., Sugita T., Shibuya S., Watanabe S., Yamaguchi H., Abe S., Okamura N. (November 2007). “Revised Culture-Based System for Identification of Malassezia Species”. J Clin Microbiol. 45(11): 3737-3742. doi: 10.1128/JCM.01243-07.
• K. A. Hammer, T. V. Riley (2000). “Precipitate production by some Malassezia species on Dixon's agar”. Med Mycol. 38 (2): 105-107. doi: 10.1080/mmy.38.2.105.107.