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Brain Heart Infusion (BHI) Agar
- 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.
Composition of Brain Heart Infusion (BHI) Agar
|HM infusion powder||12.500|
Final pH (at 25°C): 7.4±0.2
Principle of Brain Heart Infusion (BHI) Agar
- 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.
Preparation and Method of Use of Brain Heart Infusion (BHI) Agar
- Suspend 52.0 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.
- Cool to 45-50°C.
- Mix well and pour into sterile Petri plates.
Note: If desired, 20 units 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.
Result Interpretation on Brain Heart Infusion (BHI) Agar
- 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.
|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|
Uses of Brain Heart Infusion (BHI) Agar
- 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.
Limitations of Brain Heart Infusion (BHI) Agar
- 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.
- Tille, P.M., et al. Bailey and Scott’s Diagnostic Microbiology, V. Mosby Company, St. Louis, MO.