Czapek-Dox Modified Agar

Czapek-Dox Modified Agar is a semi-synthetic medium which contains sodium nitrate as a sole source of nitrogen. It has the advantage of a chemically defined formulation, which has been modified in its original formula by substituting magnesium sulfate and potassium phosphate with the magnesium glycerophosphate in this formula to prevent the precipitation of magnesium phosphate. The medium is prepared with inorganic nitrogen sources and chemically defined carbon sources only.

Sucrose is the sole fermentable carbohydrate providing carbon and energy. Sodium nitrate is the sole nitrogen source. Potassium salts act as a buffer system. Potassium chloride contains essential ions. Magnesium glycerophosphate and ferrous sulfate are sources of cations. Bacteriological agar is the solidifying agent.

Preparation

Suspend 45.4 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. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 45-50 °C, mix well and dispense into plates.

Instructions for use

1. Inoculate with a straight needle, taking the precaution to invert the plates in order to protect the medium surface from airborne spores.
2. Time and temperature of incubation vary considerably according to the fungi. As a general rule, incubate for 1-2 weeks at room temperature (approximately 25 °C). Most Penicillium grow best between 20-25 °C; Aspergillus species grow well at around 30 °C, but Aspergillus fumigatus grows well at 50 °C and C. albicans at 25 °C for 24-48 hours.

• Thom and Raper. Manual of Aspergilli. Williams and Wilkins Co., Baltimore, MD 1945.
• Smith G. An Introduction to Industrial Mycology 5th Ed. Arnold LR London, 1960.