Candida BCG Agar Base

Intended Use

Candida Bromcresol Green (BCG) Agar is a differential and selective medium used for primary isolation and detection of Candida species from clinical specimens.

Summary and Explanation

Candida BCG medium employs the formula devised by Harold and Snyder.¹ They demonstrated that the triphenyltetrazolium chloride (TTC) being used as an indicator in Pagano Levin medium retarded the growth of some species of Candida and completely inhibited the growth of others. To overcome this, they replaced TTC with bromcresol green, a non-toxic indicator, to develop Candida BCG Agar. Neomycin is incorporated to inhibit gram-negative and some gram-positive bacteria.

Principles of the Procedure

This medium consists of peptone agar base supplemented with yeast extract and dextrose to provide the nutrients necessary to support growth. Neomycin is an aminoglycoside antibiotic that is active against aerobic and facultatively anaerobic gramnegative bacteria and certain gram-positive species. Bromcresol green aids in differentiation and identification of Candida species based on dextrose fermentation. A change in the pH causes the medium to become a yellow color around the colonies of organisms that ferment dextrose.

User Quality Control

Identity Specifications
Candida BCG Agar Base
Dehydrated Appearance: Beige to blue-green, free-flowing, homogeneous.
Solution:                        6.6% solution, soluble in purified water upon
                                     boiling. Solution is blue-green to green-blue,
                                     slightly opalescent to opalescent, may have a
                                     precipitate.
Prepared Appearance:     Blue-green to green-blue, slightly opalescent to
opalescent.
Reaction of 6.6%
Solution at 25°C:            pH 6.1 ± 0.1
Cultural Response
Candida BCG Agar Base
Prepare the medium per label directions. Inoculate and incubate at 30 ± 2°C for 24-72 hours.

Formula

Candida BCG Agar Base
Approximate Formula* Per Liter
Peptone..................................................................... 10.0 g
Yeast Extract................................................................ 1.0 g
Dextrose.................................................................... 40.0 g
Agar.......................................................................... 15.0 g
Bromcresol Green....................................................... 0.02 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 66 g of the powder in 1 L of purified water. 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. Add sterile neomycin (500 μg/mL) to the medium at 50-55°C. Mix well.
5. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

Use standard procedures to obtain isolated colonies from specimens. Incubate the plates in an inverted position (agar side up) at 30 ± 2°C for up to 72 hours.

Expected Results

Candida species produce convex to cone-shaped, smooth to rough colonies. The color of the medium around the colonies becomes yellow, usually within 72 hours.
Gram staining, biochemical tests and serological procedures should be performed to confirm findings.^2-4

*Store at 2-8° C.

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