Potato Dextrose Agar (PDA) Principle, Composition, Preparation, Uses

Potato Dextrose Agar (PDA)

Potato Dextrose Agar (PDA) is commonly abbreviated as PDA.

Potato Dextrose Agar has been suggested by APHA and F.D.A.for the count of moulds and yeasts during the testing of food items and dairy products.
Potato Dextrose Agar is also utilized to promote sporulation, to keep stocks of specific dermatophytes as well as for the differentiation of common varieties of dermatophytes based on the principle on pigmentation.

It is also suggested by USP, BP, EP, and JP for the growth of the fungi.
It’s a general-purpose medium for molds and yeasts which can be supplemented by antibiotics or acids like Chloramphenicol, Tartaric Acid and Chlortetracycline are added to the mix as selective agents to hinder the growth of bacteria.
PDA is a tool to grow clinically significant yeasts and molds.

PDA can also be useful in maintaining stock cultures of some Dermatophytes.
The nutritionally rich and nutritious base of the potato infusion promotes mold sporulation as well as pigment production in certain dermatophytes, and dextrose helps to promote the development of microorganisms. Agar is a substance that solidifies.

Principle of Potato Dextrose Agar (PDA)

The potato dextrose agar (PDA) is made up of dextrose, an energy source for carbohydrate, which acts as a growth stimulant as well as potato infusion which serves as nutrients for the lush development of a wide range of fungi. Agar is used as the agent that solidifies. A specific amount of tartaric acid sterile (10 percent) can be added to reduce its pH to 3.5 so that the growth of bacteria is slowed.

It is important not to overheat the acidified medium. Heating in an acid state can make the agar hydrolyzed, which could make the agar ineligible to form a solid.

Potato Dextrose Agar Composition

Alternative Recipes For Supplemented Potato Dextrose Agar

Preparation of Potato Dextrose Agar

Dissolve 39 grams dehydrated medium (supplied by commercial vendors) in 1000ml of distilled water. Then heat to boiling, allowing it to completely dissolve the medium.
Sterilize with autoclaving at 15 pounds tension (121degC) in 15 minutes. Mix well before dispensing.
When specific work is required, pH 3.5 is needed, the medium must be acidified by tartaric acid 10% sterile. It is estimated that the amount needed for 100 milliliters. of sterile and cooled medium is around 1 milliliter. The temperature of the medium should not be increased following the introduction of the acid.

To process the specimen to be processed, you need to streak the specimen onto the medium using a sterilized inoculating loop to create isolated colonies.
Incubate the plates for 25 to 30degC with the plates in an upside-down manner (agar side facing up) with a higher humidity.
Cultures should be inspected at least every week to check to determine the growth of fungal organisms and be kept for 4 – 6 weeks before reporting as negative.

Preparation of Potato Dextrose Agar from commercial Powder

Add 39 grams of commercially powered water to 1 liter of pure water.
Boil and mix until it dissolves completely.
Sterilize media using autoclaving at 121oC for 15 mins.

Dispense aseptically into sterilized Petri dishes.

Result of Potato Dextrose Agar

Yeasts can grow from creamy-white colonies. Molds will form filamentous colonies of a variety of hues.

Colony morphology of some fungi on Potato Dextrose Agar

Fungi	Texture	Surface colour	Reverse colour	Zonation	Sporulation
Aspergillus candidus	Velvety thick	Creamy white	Slightly creamy	Radially furrowed on the reverse	Moderate
Aspergillus niger	Velvety	White with typical black spores	yellow	Heavily furrowed on the reverse	Heavy
Aspergillus sulphureus	Velvety	Dirty white with yellow spores at the centre	Orange to chocolate colour	Slighty radially furrowed	Moderate
Penicillium corylophilum	Velvety	Dark green	Colourless to Creamy	With shallow centre and radially furrowed raised margin	Moderate
P. expansum	Velvety	Dark green with clear exudates and distinct sterile white margin	Yellow	Radially furrowed	Heavy
Fusarium oxysporum	Floccose	Magenta pink	Magenta-red turning violet	With concentric zones of dark and light reddish colouration	Poor

Uses of Potato Dextrose Agar

Potato Dextrose Agar employed for the identification of molds and yeasts in dairy products and prepared food items.

It can also be employed to cultivate yeasts and molds that have been isolated from clinical samples.
Potato Dextrose Agar (TA) (Tartaric Acid) is suggested for testing of microbial contamination of food and dairy products.
Agar made from potato Dextrose Agar, containing Chlortetracycline is recommended for microbiological enumeration of yeast as well as molds from cosmetics.

Potato Dextrose Agar that contains Chloramphenicol is suggested for the selective cultivation of fungi in mixed samples.
The stock cultures of certain dermatophytes can be kept by using PDA media.
PDA is also utilized to stimulate sporulation and distinguish the most common types of dermatophytes in relation to their pigment production.

PDA is utilized for the isolation and enumeration and quantification of yeasts and the presence of molds within clinical specimens.

Limitations of Potato Dextrose Agar

It is suggested that immunological, biochemical, mass spectrometry or molecular testing be carried out on the colonies of pure culture to ensure complete identification.

References

https://microbeonline.com/potato-dextrose-agar-pda-principle-composition-colony-characteristics/

Ingredients	Gm/L
Dextrose	20 g
Potato extract	4 g*
Agar	15 g

Ingredients	Gm/L
Dextrose	20 g
Potato extract	4 g*
Agar	15 g
Chloramphenicol	25 mg ( pH-5.6 +/- 0.2 at 25°C)

Ingredients	Gm/L
Dextrose	20 g
Potato extract	4 g*
Agar	15 g
Chlortetracycline	40 mg

Ingredients	Gm/L
Dextrose	20 g
Potato extract	4 g*
Agar	15 g
tartaric acid	1.4 gm (pH-3.5 +/- 0.3 at 25°C)

Ingredients	Gm/L
Dextrose	20 g
Potato extract	4 g*
Agar	15 g
Sodium Chloride	75.0 g