Potato Dextrose Agar is a medium used for the identification, cultivation and enumeration of yeasts and molds from foodstuffs and other materials. This medium complies with the recommendations of the American Public Health Association for food and the Pharmacopoeial harmonized method for the preparation of the Aspergillus brasiliensis test strains.
TYPICAL FORMULA (g/l)
Potato Infusion (from 200 g of potatoes) Dextrose Agar 4.0
Dextrose 20.0
Agar 17.0
Final pH 5.6 ± 0.2 at 25°C
METHOD PRINCIPLE
Potato infusion and dextrose support luxuriant growth of fungi encouraging mould sporulation and pigment production. Agar is the solidifying agent.
PREPARATION
Dehydrated medium
Suspend 42 g of the powder in 1 liter of distilled or deionized water. Mix well. Heat to boil shaking frequently until completely dissolved. Sterilize in autoclave at 121°C for 15 minutes. Note: if the medium is to be used for fungal counts, it can be desirable to suppress bacterial growth. This can be done by adding 1 ml of lactic acid 10% to each 100 ml of sterilized medium at 50°C in order to acidify the pH to approximately 3.5.
Medium in bottles
Melt the content of the bottle in a water bath at 100°C (loosing the cap partially removed) until completely dissolved. Then screw the cap and check the homogeneity of the dissolved medium, if it is the case turning the bottle upside down. Cool at 45-50°C, mix well avoiding foam formation and aseptically distribute into Petri dishes.
TEST PROCEDURE
Inoculate the medium by the pour-plate method or by spread/streak technique.
Incubate aerobically at 20-25°C for 5-7 days or at 25-30°C for 18-48 h.
Experimental procedure depends on the purpose for which the medium is used.
Tubed slants are used primarily for the cultivation and maintenance of pure cultures. They should be inoculated with an inoculating loop and incubated under the same conditions as the plated medium.
INTERPRETING RESULTS
Examine the medium for fungal growth and colony morphology.
APPEARANCE
Dehydrated medium: free-flowing, homogeneous, light beige.
Prepared medium: slightly opalescent, light amber.
STORAGE
The powder is very hygroscopic, store the powder at 10-30°C, in a dry environment, in its original container tightly closed. Store bottles, tubes and prepared plates at 10-25°C away from light. Do not use the product beyond its expiry date on the label or if product shows any evidence of contamination or any sign of deterioration.
SHELF LIFE
Dehydrated medium: 4 years.
Medium in bottles: 2 years.
Medium in tubes: 1 year.
90 mm ready-to-use plates: 6 months.
WARNING AND PRECAUTIONS
Growth Good Good Good The product does not contain hazardous substances in concentrations exceeding the limits set by current legislation and therefore is not classified as dangerous. It is nevertheless recommended to consult the safety data sheet for its correct use. The product is intended for professional use only and must be used by properly trained operators.
DISPOSAL OF WASTE
Disposal of waste must be carried out according to national and local regulations in force.
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