BHI Broth: Composition, Preparation, and Why It's the Base for Blood Cultures

he problem a century of blood cultures still hasn't outgrown

A patient arrives in septic shock. Blood is drawn immediately and inoculated into blood culture bottles, the single most important diagnostic step that follows. Sepsis can be caused by almost any organism, including fastidious ones, viridans streptococci, and the notoriously slow-growing HACEK group among them, that a simple, low-nutrient broth might fail to recover at all, or recover too slowly to matter.

This exact problem is what Brain Heart Infusion broth was built to solve, and it's not a recent innovation. In 1919, Edward Rosenow was trying to grow streptococci that refused to thrive on ordinary broth. He added an infusion of calf brain tissue, and the streptococci grew. Brain and heart tissue turned out to be naturally rich in the phospholipids, growth factors, and buffering capacity that fastidious organisms need but a simple peptone broth doesn't provide.

That same nutrient-rich formula, brain and heart infusion, proteose peptone, dextrose, is still, over a century later, one of the standard broth bases used in blood culture bottles today. Every modification of BHI covered in this article exists to solve one more version of the exact problem Rosenow ran into: a broth that's rich, but not quite rich enough for one more specific fastidious organism.

Brain Heart Infusion (BHI) broth is a general-purpose liquid medium used for the cultivation and maintenance of a wide variety of fastidious and non-fastidious microorganisms, including aerobic and anaerobic bacteria, yeast, and molds, from a variety of clinical and non-clinical specimens.

Figure: Brain Heart Infusion Broth

Why Brain and Heart Tissue Specifically?

Rosenow's original insight wasn't arbitrary. Brain and heart tissue are naturally rich in phospholipids, cholesterol, and other growth factors that many fastidious organisms depend on but can't synthesize efficiently themselves. Combined with proteose peptone (carbon and nitrogen), dextrose (an energy source), disodium phosphate (buffering), and sodium chloride (osmotic balance), the result is a broth nutritionally complete enough to support organisms a simpler formula would struggle with.

Composition of Brain Heart Infusion (BHI) Broth

Storage, Preparation, and Procedure for Use

Storage conditions and Shelf life:

• Dehydrated medium: store at 10–30°C, use before the expiry date on the label.
• Prepared broth: store in the dark, below 20°C.

Procedure for use:

1. Bring the medium to room temperature before inoculation.
2. Inoculate with the specimen or organism to be cultivated.
3. For anaerobic organisms, pre-reduce the medium (e.g., by boiling and cooling, or holding in an anaerobic environment) before inoculation.
4. Incubate: aerobic organisms at 35°C with a loosened cap; fastidious organisms such as Haemophilus in a CO2-enriched atmosphere; anaerobic organisms at 35°C with a loosened cap in an anaerobic environment.

Examination schedule:

• Aerobic cultures: examine at 24 hours and again at 48 hours.
• Anaerobic cultures: examine at 48 hours.
• Re-incubate and re-examine if no growth is seen at the first check.

Interpretation of Results:

• Turbidity (cloudiness) indicates growth.
• Subculture turbid broths onto solid media to assess colony morphology and proceed with identification.

Notes:

• Yeasts and fungi may require prolonged incubation beyond the standard schedule above.
• Some strains may grow poorly regardless of incubation time, since individual organisms' nutritional requirements vary even within a species.

Uses of Brain Heart Infusion Broth, and Why Each Modification Exists

Every modification below is BHI's rich base plus one more specific answer to a fastidious-organism problem plain BHI still can't solve on its own:

For inoculum suspensions used in disk diffusion or MIC testing, BHI's role as a standardized, richly nutritious base is exactly why it can produce a reliable, reproducible starting density (see antimicrobial susceptibility testing procedure for the full inoculum preparation steps).

Key exam facts in one table

References

1. Rosenow, E. C. (1919). Studies on elective localization: focal infection with special reference to oral sepsis. Journal of Dental Research.
2. Liofilchem. Brain Heart Infusion Broth. https://www.humeau.com/media/blfa_files/TC_Brain-Heart-Infusion-Broth-55062000840-24104_EN_150518.pdf
3. Dalynn Biologicals. Brain Heart Infusion Broth. https://www.dalynn.com/dyn/ck_assets/files/tech/TB63.pdf