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This page describes products and general use; it is not medical advice.
A potato dextrose agar (PDA) plate is a Petri dish filled with a solid growth medium made from potato infusion, dextrose and agar. Its job is to grow and count yeasts and moulds. Manufacturers’ technical sheets describe it as a medium for the isolation, cultivation and enumeration of yeasts and moulds, and it is used mainly by food and dairy quality-control labs, microbiology teaching and research labs, and clinical mycology benches.
What a PDA plate is
PDA is one of the standard general-purpose fungal media. HiMedia and Thermo Fisher (Remel) give similar intended uses: HiMedia describes it for the isolation and enumeration of yeasts and moulds from water, dairy and other food products and clinical samples, and Remel describes a solid medium for the identification, cultivation and enumeration of yeast and moulds. The American Public Health Association (APHA) recommends it for yeast and mould plate counts in foods and dairy products, and the Remel sheet adds AOAC. HiMedia also notes that USP, BP, EP and JP recommend it for the growth of fungi. For the wider field, see what is mycology and what is microbiology.
Who uses it: food and dairy microbiology labs counting yeasts and moulds, academic and teaching labs growing fungal cultures, and clinical or reference labs maintaining dermatophyte stock cultures.
Composition and how it is made
The classical formula is the same on both sheets. Each ingredient has a role: potato infusion supplies nutrients, dextrose is the sugar energy source, and agar is the gelling agent that makes the medium solid. The final pH is 5.6 plus or minus 0.2 at 25 C, a mildly acidic value.
| Component | Amount per litre | Role |
|---|---|---|
| Potato infusion (from 200 g potatoes; 4.0 g solids) | 4.0 g | Nutrient base |
| Dextrose | 20.0 g | Carbohydrate energy source |
| Agar | 15.0 g | Solidifying agent |
| Powder total | 39 g (HiMedia GM096 and Remel IFU 454311) | Suspend in 1,000 ml purified or demineralised water |
Both sheets state the formula is adjusted as required to meet performance standards, so exact values can vary slightly by lot. For dehydrated media, both sheets direct that the powder is dissolved in water by heating, sterilised by autoclaving at 121 C for 15 minutes, and cooled before dispensing; HiMedia gives 45-50 C as the cooling target. See what is an autoclave for how that sterilising step works. The prepared medium is described as yellow and clear to slightly opalescent, and it should gel firmly, comparable with 1.5% agar (HiMedia).
Standard versus acidified PDA
Both manufacturers describe lowering the pH to 3.5 with sterile 10% tartaric acid to inhibit bacterial growth. The two sheets differ on how much acid to add.
| Variant | Final pH | Typical use | Key difference |
|---|---|---|---|
| Standard PDA | 5.6 +/- 0.2 at 25 C | General growth and counts of yeasts and moulds; sporulation; dermatophyte stock cultures | No added acid (HiMedia GM096; Remel IFU 454311) |
| Acidified PDA | 3.5 | Yeast and mould counts where bacterial growth must be inhibited | Sterile 10% tartaric acid added to sterile, cooled medium; the medium must not be heated afterwards (HiMedia GM096) |
The acid volume is manufacturer-specific. HiMedia gives approximately 1 ml of sterile 10% tartaric acid per 100 ml of sterile cooled medium; the Remel sheet gives 1.8 ml per 100 ml of cooled sterilised base. Follow the instructions supplied with your own lot rather than mixing figures from different sheets. HiMedia states plainly: do not heat the medium after the acid is added. Heating acidified agar can hydrolyse the agar so that it will not solidify.
What PDA is used for
- Yeast and mould counts in food and dairy: recommended by APHA for plate counts in foods and dairy products (HiMedia; Remel, which also cites AOAC).
- Stimulating sporulation: used in slide-culture preparations to encourage spore formation (Remel).
- Dermatophytes: used to maintain stock cultures of certain dermatophytes, and to differentiate dermatophyte varieties by pigment production (HiMedia; Remel, which credits Rebell and Taplin for atypical dermatophytes).
- Compendial fungal growth: recommended by the USP, BP, EP and JP for the growth of fungi (HiMedia).
Quality control organisms
Manufacturers verify each lot against reference strains, which also shows what the medium is designed to grow. After incubation at 20-25 C for 2-7 days, HiMedia reports luxuriant growth of Aspergillus brasiliensis ATCC 16404, Candida albicans ATCC 10231 and Saccharomyces cerevisiae ATCC 9763, and fair to good growth of Trichophyton rubrum ATCC 28188. Remel lists Candida albicans ATCC 10231, Cryptococcus neoformans ATCC 34877 and Trichophyton mentagrophytes ATCC 9533, with good growth after up to 72 hours at 25-30 C. The two sheets use different strain panels and conditions, another reason to read the sheet that matches the lot you hold.
Choosing and storing
The useful checks are about matching the medium to its label:
- Check the labelled intended use. HiMedia labels its product “In Vitro diagnostic Use. For professional use only.” Remel labels its product “For Laboratory Use only. It is not intended for use in the diagnosis of disease.” Confirm which labelling applies to the product you hold before using results for any purpose.
- Decide whether you need acidified medium and, if so, take the acid volume from the sheet for your lot.
- Storage: HiMedia states the dehydrated powder should be kept at 10-30 C in a tightly closed container because it is hygroscopic and lumps with moisture, and the prepared medium at 20-30 C; use before the expiry date.
Safe use and handling basics
HiMedia calls for good microbiological practice, with gloves, protective clothing and eye protection, and states that contaminated materials must be autoclaved before disposal (by autoclaving and/or incineration). Remel directs users to established laboratory procedures. Plates that may carry fungal cultures should be handled under the biosafety practices of your laboratory; see BSL-2 and biosafety cabinet for the reference terms, and what is an incubator for incubation equipment. Culture contamination is covered in cell culture contamination.
Common mistakes
- Reheating after adding acid. This can hydrolyse the agar so it will not set (HiMedia).
- Assuming one acid volume fits all brands. HiMedia gives approximately 1 ml and Remel 1.8 ml per 100 ml.
- Pouring too hot. HiMedia directs cooling to 45-50 C before dispensing.
- Treating a research-use plate as a diagnostic one. The labelling differs between products; follow the label.
- Letting powder absorb moisture. The powder is hygroscopic; keep the container tightly closed.
FAQ
What is a potato dextrose agar plate used for?
Growing, isolating and counting yeasts and moulds, including plate counts in foods and dairy, stimulating sporulation, and maintaining certain dermatophyte stock cultures.
What is in potato dextrose agar?
Potato infusion (4.0 g solids per litre, from 200 g potatoes), dextrose 20.0 g, agar 15.0 g, at a final pH of about 5.6, per the HiMedia and Remel sheets.
How do you make PDA acidic?
Add sterile 10% tartaric acid to sterile cooled medium to reach pH 3.5, using the volume stated by the manufacturer of your lot, and do not heat the medium afterwards.
Sources
- HiMedia Laboratories, Technical Data GM096, Potato Dextrose Agar, Granulated: https://www.himedialabs.com/media/TD/GM096.pdf (checked 2026-10-29).
- Thermo Fisher Scientific (Remel), Instructions for Use IFU454311, Potato Dextrose Agar, revision 21 Oct 2010: https://documents.thermofisher.com/TFS-Assets/LSG/manuals/IFU454311.pdf (checked 2026-10-29).
