Mycological Agar

Intended Use

Mycological media are used for the cultivation and maintenance of fungi, for the demonstration of chromogenesis and for obtaining yeast and mold counts.

Summary and Explanation

Many different culture media have been developed for the growth of fungi. In comparison with media for the majority of bacterial strains, fungal media are of simple composition, usually consisting of a peptone, dextrose and agar. Selectivity is achieved by lowering the pH, incorporating dyes or adding antimicrobial agents.
Mycological Agar and Mycophil Agar are nonselective media of value in general work with yeasts and molds rather than for isolation from materials possessing mixed flora. It is often desirable to use these media in parallel with selective media as some of the selective agents are inhibitory for certain fungi.
Mycophil Agar with Low pH has had its base adjusted to approximately pH 4.7, which obviates the need for pH adjustment with lactic or tartaric acids in the laboratory. It also differs from Mycophil Agar in that an additional 2 g/L of agar has been incorporated so that the medium may be sterilized and remelted without losing its ability to solidify.
Wetzler et al. employed Mycophil Agar with Low pH for enumeration of yeasts and molds in poultry processing plants.¹ The formulation also has been recommended for isolation of yeasts and most filamentous fungi from clinical material.²

Principles of the Procedure

The peptone and dextrose ingredients supply sufficient nutrients for the metabolism of fungal species.

User Quality Control

Identity Specifications
Mycological Agar
Dehydrated Appearance: Light beige, free-flowing, homogeneous.
Solution:                        3.5% solution, soluble in purified water upon
                                     boiling. Solution is light to medium amber, very
                                     slightly to slightly opalescent.
Prepared Appearance:     Light to medium amber, slightly opalescent.
Reaction of 3.5%
Solution at 25°C:            pH 7.0 ± 0.2
Cultural Response
Mycological Agar
Prepare the medium per label directions. Inoculate and incubate at 30 ± 2°C (incubate Penicillium at 20-25°C) for 18-72 hours. 

Formula

Mycological Agar
Approximate Formula* Per Liter
Soy Peptone............................................................... 10.0 g
Dextrose.................................................................... 10.0 g
Agar.......................................................................... 15.0 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 35 g of the powder in 1 L of purified water. Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes.
4. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

Inoculate plated media with test specimens or materials so as to obtain isolated colonies. Consult appropriate references for information about the processing and inoculation of specimens.^3,4 For isolation of fungi from potentially contaminated specimens, also inoculate a selective medium. Incubate plates at 25-30°C in an inverted position (agar side up) with increased humidity. For isolation of fungi causing systemic mycoses, two sets of media should be inoculated, with one set incubated at 25-30°C and a duplicate set at 35 ± 2°C. All cultures should be examined at least weekly for fungal growth and should be held for 4-6 weeks before being reported as negative.

Expected Results

After sufficient incubation, the plates should show isolated colonies in streaked areas and confluent growth in areas of heavy inoculation. Examine plates for fungal colonies exhibiting typical color and morphology. Yeast and mold colonies can be counted to determine the level of contamination in the test sample. Biochemical tests and serological procedures should be performed to confirm findings.⁵

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