Brain Heart Infusion (BHI) Agar- Composition, Principle, Preparation, Results, Uses

In 1919, Rosenow devised an excellent medium for culturing streptococci by using a dextrose broth supplemented with brain tissue.
Rosenow’s formulation was later modified by Hayden who found the addition of crushed marble resulted in favorable growth of dental pathogens.
Our current formulation contains infusion from calf brain in place of brain tissue and disodium phosphate has replaced calcium carbonate.
Brain Heart Infusion (BHI) Agar is a highly nutritious base that meets the growth requirements of many types of microorganisms including bacteria, yeasts, and molds.
BHI Agar supplemented with (5 to 10%) defibrinated sheep blood is used extensively for the recovery of dimorphic fungi such as Histoplasma capsulatum and other pathogenic fungi such as Coccidioides immitis.
A more selective formulation containing chloramphenicol and cycloheximide is also available that will allow the recovery of pathogenic fungi while inhibiting a wide range of bacteria and saprophytic fungi.
BHI Agar is thus a solid medium recommended for the cultivation of fastidious pathogenic bacteria, yeasts, and molds from clinical and non-clinical samples.

Table of Contents

Composition of Brain Heart Infusion (BHI) Agar

Final pH (at 25°C): 7.4±0.2

Brain Heart Infusion has proven to be effective in the cultivation of a wide variety of microorganisms, including many types of pathogens. It has served as the base medium for new culture media formulations when supplemented with blood or with selective agents.
Brain Heart Infusion (BHI) Agar derives its nutrients from the brain heart infusion, peptone and glucose components.
Protease peptone and infusions used in the media serve as sources of carbon, nitrogen, vitamins, amino acids, along with essential growth factors.
Dextrose is the energy source.
Sodium chloride maintains the osmotic equilibrium of the medium while disodium phosphate buffers the medium.
Defibrinated sheep blood added to the basal medium provides essential growth factors for the more fastidious fungal organisms.

Note: If desired, 20 units of Penicillin and 40 µg Streptomycin per ml of the medium may be added to make the medium selective for fungi.

Streak the specimen as soon as possible after it is received in the laboratory using a sterile inoculating loop to obtain isolated colonies.
For isolation of fungi from potentially contaminated specimens, a selective medium should be inoculated along with the nonselective medium.
Incubate the plates at 25 to 30°C in an inverted position with increased humidity.
For isolation of fungi causing systemic mycoses and the isolation of aerobic Actinomycetales, two sets of media should be inoculated, with one set incubated at 25 to 30°C and a duplicate set at 35 to 37°C.
Depending on the clinical diagnosis and the agents suspected to cause the infection, other media should be included.
All cultures should be examined at least weekly for growth and should be held for several weeks before being reported as negative.

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

Organisms	Growth
Candida albicans	Luxuriant growth
Staphylococcus aureus subsp. aureus	Luxuriant growth
Streptococcus pneumoniae	Luxuriant growth; grey-green colored colonies
Shigella flexneri	Luxuriant growth
Escherichia coli	Luxuriant growth
Listeria monocytogenes	Growth good to excellent
Trichophyton mentagrophytes	Growth good to excellent
Neisseria meningitidis	Good growth; grey-brown colored colonies

Brain Heart Infusion Agar is highly nutritious and can support a luxuriant growth of a wide variety of microorganisms.
It can be further enriched by the addition of blood or rendered selective by adding different antibiotics.
It is a general purpose medium used for primary isolation of aerobic bacteria from clinical specimens.
Addition of 50 mg/l chloramphenicol or 40mg/l streptomycin or a mixture of 50mg/l gentamicin and 50mg/l chloramphenicol along with 5-10% sterile defibrinated blood is often recommended for inhibition of bacteria and isolation of pathogenic systemic fungi.
Without supplementation, Brain Heart Infusion (BHI) Agar currently is recommended as a universal medium for aerobic bacteriology and for the primary recovery of fungi and Actinomycetales from clinical specimens and from nonclinical materials.

As organisms differ in their nutritional requirements, some fastidious organisms may be inhibited or may show poor growth.
Further biochemical tests must be carried out for complete identification.
Due to the non-selective nature of BD Brain Heart Infusion (BHI) Agar, specimens heavily contaminated with normal flora should also be streaked onto appropriate selective media to avoid overgrowth by the contaminating organisms.
If fastidious organisms known to require blood for growth are suspected, Brain Heart Infusion Agar with 10% Sheep Blood should be used.