Potato Dextrose Broth

Intended Use

Potato Dextrose Broth is used for cultivating yeasts and molds.

Potato Dextrose Agar meets United States Pharmacopeia (USP), European Pharmacopoeia (EP) and Japanese Pharmacopoeia (JP)1-3 performance specifications, where applicable.

Summary and Explanation

Potato Dextrose Broth is a general-purpose broth medium for yeasts and molds (Potato Dextrose Agar without the agar).

Principles of the Procedure

Potato starch, potato infusion and dextrose support luxuriant growth of fungi. Lowering the pH of the medium to approximately 3.5 with sterile tartaric acid achieves the inhibition of bacterial growth. It is important, however, to avoid heating the medium after it has been acidified because this action results in the hydrolysis of the agar and impairs its ability to solidify.

User Quality Control

Identity Specifications
Potato Dextrose Broth
Dehydrated Appearance: Light beige, free-flowing, homogeneous.
Solution:                       2.4% solution, soluble in purified water upon
                                    boiling. Solution is very, very light amber, clear
                                    to very slightly opalescent.
Prepared Appearance:     Very, very light amber, clear to very slightly opalescent.
Reaction of 2.4%
Solution at 25°C:            pH 5.1 ± 0.2
Cultural Response
Potato Dextrose Broth
Prepare the medium per label directions. Inoculate and incubate at 25 ± 2°C for 40-48 hours.

Formula

Potato Dextrose Agar
Approximate Formula* Per Liter
Potato Starch (from infusion)**...................................... 4.0 g
Dextrose.................................................................... 20.0 g
Agar.......................................................................... 15.0 g
*Adjusted and/or supplemented as required to meet performance criteria.
**Approximates 200 g of infusion from potatoes.
Potato Dextrose Broth
Consists of the same ingredients without the agar.

Directions for Preparation from Dehydrated Product

1. Suspend the powder in 1 L of purified water:
    Potato Dextrose Broth – 24 g.
    Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes.
4. To alter the reaction of the agar medium to pH 3.5, cool the base to 45-50°C and aseptically add an appropriate amount of sterile 10% tartaric acid to each liter of medium. Mix well.
Do not reheat the medium.
5. Test samples of the finished product for performance using stable, typical control cultures.

Sample Collection and Handling

For clinical specimens, refer to laboratory procedures for details on specimen collection and handling.^8,9

For food, dairy and cosmetic samples, follow appropriate standard methods for details on sample collection and preparation according to sample type and geographic location.^4,7

For pharmaceutical samples, refer to the USP for details on sample collection and preparation for testing of nonsterile products.¹

Procedure

For clinical specimens, refer to appropriate standard references for details on testing protocol to obtain isolated colonies from specimens using Potato Dextrose Agar.^8,9

For food, dairy and cosmetic samples, refer to appropriate standard references for details on test methods using Potato Dextrose Agar.^4-7

For pharmaceutical samples, refer to USP General Chapter for details on the examination of nonsterile products and Microbial Enumeration Tests using Potato Dextrose Agar.¹

Liquefy the medium in pour tubes by heating in boiling water. Cool to 45-50°C and pour into sterile Petri dishes. Allow to solidify for a minimum of 30 minutes.

Streak the specimen onto prepared media with a sterile inoculating loop to obtain isolated colonies. When used for determining yeast and mold counts, the medium should be adjusted to a pH of approximately 3.5 with sterile tartaric acid and used in the standard pour plate technique. Incubate the plates at 25-30°C with increased humidity for up to 7 days.

Tubed slants are used primarily for the cultivation and maintenance of pure cultures. They should be inoculated with an inoculating loop and incubated under the same conditions as the plated medium.

For isolation of fungi from potentially contaminated specimens, a selective medium should be inoculated along with the nonselective medium. For isolation of fungi causing systemic mycoses, two sets of media should be inoculated, with one set incubated at 25-30°C and a duplicate set at 35 ± 2°C. All cultures should be examined at least weekly for fungal growth and should be held for 4-6 weeks before being reported as negative.

Inoculation of Potato Dextrose Broth with pure cultures of yeasts can assist in their identification.

Expected Results

After sufficient incubation, the plates which were streak inoculated should show isolated colonies in streaked areas and confluent growth in areas of heavy inoculation. The colonies in pour plates should be counted and the results expressed as yeast and mold counts per gram or milliliter of material, taking into account the applicable dilution factor.

Growth from tubes inoculated with pure cultures may be used for biochemical and/or serological testing.

For broth, observe cultures for surface growth and pellicle formation.

Limitations of the Procedure

1. Heating Potato Dextrose Agar after acidifying hydrolyzes the agar and may destroy the solidifying properties.
2. Potato Dextrose Agar is not a differential medium. Perform microscopic examination and biochemical tests to identify isolates to genus and species if necessary.

*Store at 2-8° C.

Free Shipping within the Continental USA