Yeast Dextrose Agar

Intended Use

Yeast Dextrose Agar is used for the cultivation of a variety of heterotrophic microorganisms.

Composition

Final pH (at 25°C): 7.0±0.2

Formula adjusted, standardized to suit performance parameters.

Directions

Suspend 35 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Mix well and pour into sterile Petri plates.

Principle and Interpretation

Heterotrophic microorganisms are those that use organic matter synthesized by other organisms for energy and growth. The terminal electron acceptor in the electron transport chain is an organic compound instead of oxygen.

Heterotrophic organisms that feed exclusively on dead organic matters such as rotting wood are called as saprophytes. Heterotrophs that feed on living organic matter such as human tissues are commonly known as parasites. Fungal cells lack chlorophyll and photosynthesis is therefore impossible. Since they consume preformed organic matter, fungi are described as heterotrophic microorganisms. Together with bacteria, fungi decompose vast quantities of dead organic matter. Yeast Dextrose Agar is recommended for isolation and cultivation of various heterotrophic organisms (1). Yeast extract in the medium is the source of nitrogen and growth factors while dextrose provides an energy source for the growth of microorganisms.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Gelling: Firm, comparable with 1.5% Agar gel.

Colour and Clarity of prepared medium: Light yellow coloured clear to slightly opalescent gel forms in Petri plates.

Reaction: Reaction of 3.5% w/v aqueous solution at 25°C. pH: 7.0±0.2

pH: 6.80-7.20

Cultural Response: M1199: Cultural characteristics observed after an incubation at 30°C for 24-48 hours.

*- formerly known as Aspergillus niger

Storage and Shelf Life

Store below 30°C in tightly closed container and prepared medium at 2-8° C. Use before expiry period on the label.

References

1. Atlas R. M., Handbook of Microbiological Media. 3rd Edition, 2004, CRC Press.