Potato Dextrose Agar Principle,Composition and Colony characteristics

Black Mold Aspergillus niger on Potato Dextrose agar

Potato dextrose agar is a fungi growth media recommended for the isolation and counting of yeasts and moulds from dairy products and other foodstuffs.

It is also used for stimulating sporulation,maintaining stock cultures of certain dermatophytes and for the differentiation of typical varieties of dermatophytes on the basis of pigment production.

Principle of Potato Dextrose Agar

  • Potato infusion and dextrose promote abundant fungal growth.
  • Adjustment of the pH value of the medium by tartaric acid to 3.5, inhibits bacterial growth.
  • Heating of the medium after acidification should be avoided as it may hydrolyse the agar, which may prevent the agar from solidifying.

Composition of Potato Dextrose Agar

The following ingredients are used for the composition potato dextrose agar

IngredientsGrams / Litre
Potatoes, infusion from200.000
Dextrose 20.000
Agar15.000
Final pH at temperature  25°C5.6±0.2

How to Prepare Potato Dextrose Agar

  • Start by suspending 39 grams in 1000 ml distilled water.
  • Now heat to boiling in order to dissolve the medium completely.
  • Sterilize the medium by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
  • Then mix well before dispensing. In specific work, when pH 3.5 is required, acidify the medium with sterile 10% tartaric acid or  lactic acid.
  • The amount of acid required for 100 ml of sterile, cooled medium is approximately 1 ml.
  • Take note not to heat the medium after addition of the acid.

NB: It is also advisable to incubate a petri dish for 24 hour for quality control in order to avoid wastage of resources and ease early detection of contamination after of the batch of culture media prepared.

Also read  Normal Flora and Their Various Location in the Body

Appearance of Medium after preparation

It appears light amber coloured clear to slightly opalescent gel forms when poured in Petri dishes

Uninoculated Potato dextrose agar
Uninoculated Potato dextrose agar

Type of Inoculums

  • dairy products
  • other foodstuffs
  • Biological specimens

Plate reading and Colonies morphology

These cultural characteristics are observed after incubation of the inoculated medium at a temperature of  20-25 °C for 2-5 days.

OrganismGrowthIncubation temperatureIncubation period
Candida albicans luxuriant20 -25 °C2 -3 days
Aspergillus brasiliensis luxuriant20 -25 °C5 -7 days
Aspergillus fumigatusluxuriant20 -25 °C5 -7 days
Saccharomyces cerevisiaeluxuriant30 -35 °C2 -5 days
Rhodotorula mucilaginosaluxuriant20 -25 °C 3 -5 days
Geotrichum candidum good- luxuriant25 -30 °C3 -5 days
Penicillium communefair -good25 -30 °C3 -5 days
Trichophyton ajelloifair-good 25 -30 °C3 -7 d
Fusarium solani  luxuriant20 -25 °C3 -5 d
Aspergillus niger in potato dextrose agar
Aspergillus niger (Black mold) in potato dextrose agar
Mucor species
Mucor species 
Penicillium roqueforti in potato dextrose agar
Penicillium roqueforti in potato dextrose agar

Reference

  • Downes F. P. and Ito K., (Eds.), 2001, Compendium of Methods for the Microbiological Examination of Foods, 4th Ed., APHA, Washington, D.C.
  • FDA Bacteriological Analytical Manual, 2005, 18th Ed., AOAC, Washington, DC.
  • Wehr H. M. and Frank J. H., 2004, Standard Methods for the Microbiological Examination of Dairy Products, 17th Ed., APHA Inc., Washington, D.C.
  • MacFaddin J. F., 1985, Media for the Isolation-Cultivation-Identification-Maintenance of Medical Bacteria, Vol.1, Williams and Wilkins, Baltimore
  • The United States Pharmacopoeia, 2016, The United States Pharmacopoeial Convention. Rockville, MD.

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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