Sabouraud Brain Heart Infusion Agar Base

Intended Use

Sabouraud Brain Heart Infusion Agar is used in qualitative procedures for cultivation of dermatophytes and other pathogenic and nonpathogenic fungi from clinical and nonclinical specimens. The medium is rendered selective by the addition of antimicrobial agents.

Summary and Explanation

Sabouraud Brain Heart Infusion Agar is based on the formulation of Gorman.¹ The combination of Brain Heart Infusion Agar and Sabouraud Dextrose Agar in this medium improves the recovery of fungi compared with the recovery on either medium individually. The addition of defibrinated sheep blood is recommended to increase the recovery of fastidious, dimorphic fungi.²
The antimicrobial agents chloramphenicol, cycloheximide and gentamicin are incorporated in various combinations to improve the recovery of pathogenic fungi from specimens heavily contaminated with bacteria and saprophytic fungi.²

Principles of the Procedure

Peptones and brain heart digest are sources of amino acids, nitrogen, sulfur, carbon and trace ingredients. Dextrose is an energy source for the metabolism of microorganisms. Sodium chloride provides essential electrolytes. Disodium phosphate buffers the medium to maintain the pH. Defibrinated sheep blood is added to supply nutrients that induce the growth of dimorphic species in the yeast phase.²
Chloramphenicol is a broad-spectrum antibiotic that inhibits a wide range of gram-negative and gram-positive bacteria. Cycloheximide is an antifungal agent that is primarily active against saprophytic fungi and does not inhibit pathogenic species. Gentamicin is an aminoglycoside antibiotic that inhibits the growth of gram-negative bacteria.

User Quality Control

Identity Specifications
Sabouraud Brain Heart Infusion Agar Base
Dehydrated Appearance: Light beige, free-flowing, homogeneous.
Solution:                        5.9% solution, soluble in purified water upon
                                     boiling. Solution is medium amber, very slightly to
                                     slightly opalescent.
Prepared Appearance:     Medium amber, very slightly to slightly opalescent.
Reaction of 5.9%
Solution at 25°C:             pH 7.0 ± 0.2
Cultural Response
Sabouraud Brain Heart Infusion Agar Base
Prepare the medium per label directions without (plain) and with 10% sheep blood (SB). Inoculate and incubate at 30 ± 2°C for 18-48 hours and up to 7 days for Trichophyton.

Formula

Sabouraud Brain Heart Infusion Agar Base
Approximate Formula* Per Liter
Brain Heart Digest........................................................ 9.25 g
Proteose Peptone........................................................... 5.0 g
Enzymatic Digest of Casein............................................. 5.0 g
Dextrose..................................................................... 21.0 g
Sodium Chloride............................................................ 2.5 g
Disodium Phosphate..................................................... 1.25 g
Agar........................................................................... 15.0 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 59 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. Cool to 50-55°C.
4. Aseptically add 1 mL chloramphenicol solution (100 mg/mL) and, if desired, 10% sterile sheep blood.
5. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

Use standard procedures to obtain isolated colonies from specimens.
For isolation of fungi from potentially contaminated specimens, both a nonselective and a selective medium should be inoculated. Incubate the plates at 25-30°C in an inverted position (agar side up) with increased humidity. 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.

Expected Results

After sufficient incubation, the plates should show isolated colonies in streaked areas and confluent growth in areas of heavy inoculation.
Examine the plates for fungal colonies exhibiting typical color and morphology. Biochemical tests and serological procedures should be performed to confirm findings.

Limitations of the Procedure

Some fungi may be inhibited by the antibiotics in selective formulations.^3,4

*Store at 2-8° C.

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