Description: Potato Dextrose promotes the growth of yeasts and molds, while the low pH inhibits the growth of bacterial flora. It is used to isolate and cultivate yeasts and molds in dairy and food products.
Selective For: Yeasts and molds
Composition: Potato infusion, dextrose and yeast extract. pH 3.7 ± 0.2. Chloramphenicol is added to further inhibit bacterial growth.
Procedure: Standard Methodology for product being tested.
Incubation time and temperature: 2 to 5 days at 25-30°C.
Interpretation: Yeast colonies tend to grow as small, shiny, white to off-white colonies with defined, smooth borders. They emit a characteristic “fresh bread” odor. Molds which are very young and growing inside the medium will have a hair-like appearance when viewed under a microscope. Molds growing inside the medium will not become colored until they grow to the surface. Molds growing on the surface will usually exhibit colors due to sporulation (green, gray, black or other colors), and will appear fuzzy. Lactic acid bacteria may sometimes break through the pH barrier of standard Potato Dextrose Easygel® and grow with a morphology similar to yeast colonies. Heavy growth of lactic acid bacteria will tend to have a sour smell as opposed to the bread odor of a pure yeast culture.
Optimal storage is freezing due to the antibiotic. If to be used within 1 month, room temperature is acceptable. If storing for more than 1 month, refrigerate or freeze.
Shelf Life: 1 year
Easygel® is a registered trademark of Micrology Laboratories