Rosenow developed a medium that could be used to cultivate streptococci using a dextrose broth and brain tissue in 1919. Hayden modified Rosenow’s formula and found that crushed marble promoted the growth of dental pathogens. The current formulation uses infusions from calf brain instead of brain tissue, and disodiumphosphate has been replaced by calcium carbonate.
Brain Heart Infusion (BHI), Agar, is a nutritious base that can be used to grow many kinds of microorganisms such as yeasts, bacteria, and molds. BHI Agar is supplemented with 5 to 10% defibrinated sheep’s blood. This is widely used for the recovery dimorphic fungi like Histoplasma capsuleum and other pathogenic fungal species such as Coccidioides impitis.
There is also a more specific formulation that contains cycloheximide and chloramphenicol. This will allow for the recovery of pathogenic and inhibited bacterial species. BHI Agar is a solid medium that can be used to cultivate fastidious pathogenic bacteria and yeasts. It can also be used for 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 been proven to be very effective in cultivating a variety of microorganisms including pathogens. When supplemented with blood, or with select agents, it has been used as a base medium for the creation of new media media. Brain Heart Infusion (BHI), Agar gets its nutrients from the brain infusion, peptone, and glucose components. Infusions and prototease peptone are used as sources of carbon, nitro, vitamins, amino acid, and other essential growth factors. Dextrose is the main energy source. Disodium phosphate and sodium chloride buffer the medium. The basal medium can be supplemented with defibrinated sheep’s blood to provide essential growth factors for more complex fungal organisms.
Preparation and Method of Use of Brain Heart Infusion (BHI) Agar
- Take 52.0 grams and mix it with 1000 ml of distilled water.
- To dissolve the medium completely, heat to boiling
- For 15 minutes, sterilize by using an autoclave at 15 lbs pressure (121degC).
- Keep it at 45-50 degrees Celsius
- Mix everything together and pour onto sterilized Petri dishes.
To make the medium more selective for fungi, you can add 20 units Penicillin or 40 ug Streptomycin to each ml.
- To obtain isolated colonies, you should immediately begin to treat the specimen once it has been received at the laboratory.
- A selective medium must be used inoculating with nonselective media to isolate fungi from potentially contaminated specimens.
- Place the plates in an inverted position and add more humidity to incubate them at 25-30C.
- Two sets of media are required to inoculate fungi that cause systemic mycoses or the isolation of aerobic Actinomycetales. One set should be incubated at 25-30degC, and another set at 35-37degC.
- Other media may be added depending on the diagnosis and agents that are suspected of causing the infection.
- Each culture should be checked at least once a week for growth.
Result Interpretation on Brain Heart Infusion (BHI) Agar
- After enough incubation, plates should display isolated colonies in streaked regions and confluent growth where there has been heavy inoculation.
- Check plates for fungal or bacterial colonies that exhibit typical coloration and morphology.
- To confirm findings, biochemical tests and/or microscopical or serological procedures should be done.
|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 can be very nutritious and support the luxuriant growth a variety of microorganisms.
- You can enrich it further by adding blood, or make it more selective by using different antibiotics.
- It can be used to isolate aerobic bacteria from clinical specimens.
- For the isolation of pathogenic systemic fungal infections and inhibition of bacteria, it is common to add 50 mg/l chloramphenicol and 40mg/l Streptomycin.
- Brain Heart Infusion (BHI), Agar is currently recommended for use as an unsupplemented medium for aerobic bacteriology, and primary recovery of Actinomycetales and fungi from clinical specimens or other nonclinical materials.
Limitations of BHI Agar
- Because organisms have different nutritional needs, some organisms might be slow to grow or show poor growth.
- Additional biochemical tests are required to confirm the identification.
- Because BD Brain Heart Infusion Agar is non-selective, specimens contaminated with normal flora should be streaked onto suitable selective media to prevent overgrowth by the contaminating organisms.
- Brain Heart Infusion Agar containing 10% Sheep Blood should only be used if fastidious organisms are suspected to need blood for growth.