Agar Plates are media plates used for culturing microorganisms like bacteria and fungi. Potato dextrose agar is used for fungal cultivation. This is a general-purpose medium used for molds and yeasts. This media can be supplemented furthermore with antibiotics or acid to inhibit the growth of bacteria. The nutritionally rich base of this media supports mold sporulation and dermatophyte pigment production. This media is used in the food, dairy, and cosmetic industry commonly.
Principle of Potato Dextrose Agar
This media is composed of dehydrated potato infusion and dextrose, thus encouraging fungal growth. Agar is added as a solidifying agent for the media to be plated. In the case of potato dextrose agar media plates, many standard procedures report the use of sterile tartaric acid to lower the pH of the media to around 3.5, which helps to inhibit bacterial growth. Moreover, chloramphenicol can be added as a selective agent that inhibits bacterial growth in mixed specimens, thus promoting selective fungal isolation.
Point to Note: It is advised not to reheat the media after acidifying it as it will hydrolyze the agar.
Uses of Potato Dextrose Agar
This media plate is generally used for detecting yeasts and molds in the prepared foods and dairy products. These media plates are also used for the cultivation of molds and yeasts from clinical specimens. Researchers and quality control personnel use potato dextrose media for microbial examination of dairy and food products.
Composition of Potato Dextrose Agar
Preparing the media from scratch:
Note: 200 gm of potato infusion ~ 4.0 gm of potato extract.
Preparing the media from commercial media powder
Commercial PDA Powder (20 gm dextrose, 15 gm agar, and 4 gm potato starch)
Products that can be additionally supplemented to the media:
(Final pH of 5.6 +/- 0.2 at 25 degree Celsius)
With Tartaric acid:
(Final pH of 3.5 +/- 0.3 at 25 degrees Celsius)
Colony Characteristics of Growth
After sufficient incubation of the cultured potato dextrose media plates, the isolated colonies will be visible in the streaked areas while confluent growth will be visible in the areas of heavy inoculation.
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