Pyruvate Broth Utilization
A bench guide to Pyruvate Broth, used to differentiate Enterococcus faecalis (positive) from Enterococcus faecium (negative) based on their ability to utilize pyruvate.
Pyruvate tubes A-B
Differentiate pyruvate utilization (yellow) from a negative reaction (green) in a carbohydrate-free, nutrient-limited medium.
The bromthymol blue indicator changes from green to yellow, demonstrating the production of metabolic acids from pyruvate utilization.
Broth remains deep green/blue-green, indicating the organism cannot utilize pyruvate (yellow-green is regarded as negative).
The bromthymol blue indicator changes from green to yellow, demonstrating the production of metabolic acids from pyruvate utilization.
Broth remains deep green/blue-green, indicating the organism cannot utilize pyruvate (yellow-green is regarded as negative).
What to look for
| Visual clue | Meaning | Student shorthand |
|---|---|---|
| Yellow color | Acid accumulation from the utilization of pyruvic acid, lowering pH | Positive reaction |
| Deep green/blue-green | No pyruvate utilization; pH remains neutral/basic | Negative reaction |
| Yellow-green color | Weak, clinically insignificant shift; must be interpreted as negative | Regarded as negative |
Pyruvate Interpretive Matrix
| Pattern | What to call it | How to think about it |
|---|---|---|
| Bright yellow broth | Positive | Organism utilizes pyruvate (e.g., Enterococcus faecalis). |
| Green, blue-green, or yellow-green | Negative | Organism does not utilize pyruvate (e.g., Enterococcus faecium). |
- Pyruvate broth tests the ability to utilize pyruvate as an energy source in a carbohydrate-free, nutrient-limited medium.
- Bromthymol blue is the pH indicator: yellow is acid (positive), green is neutral/alkaline (negative).
- It is highly specific for separating Enterococcus species in clinical diagnostic paths.
Pyruvate = Yellow (Positive) for Enterococcus faecalis. Green = Negative for Enterococcus faecium.