Phenol Red Dextrose (PRD)

Detection of Acid Producing Bacteria (APB) and General Heterotrophic Bacteria (GHB)

What is PRD?

  • PRD is a nutrient broth that is the NACE TMO-194 Standard for the detection of Acid Producing Bacteria (APB)
  • PRD is historically an aerobic media to facilitate the cultivation of aerobic and facultative organisms

How It Works

  • PRD contains nutrients such as proteins and sugars as well as a colorimetric acid indicator
  • When APB bacteria metabolize the nutrients in the solution, they will create organic acids. These organic acids will lower the pH of the solution and the acid indicator will go from red to yellow/orange.
  • Some bacteria can grow in this solution and not produce acid. These bacteria will cause the vial to become turbid or cloudy as biomasses form, however the vials will not turn yellow. These bacteria are known as General Heterotrophic Bacteria (GHB)

False Positive

If the pH of a liquid inoculated into the media is low, such as waters containing acidic biocides or chemicals, the vial may immediately turn yellow. This is considered a false positive. Typically, false positive PRD will be yellow without any visible turbidity.