L-Pyrrolidonyl Arylamidase (PYR) Test
A bench guide to the PYR test, used for the presumptive identification of Group A streptococci (S. pyogenes) and Enterococci by detecting PYRase activity.
PYR reaction cards A-B
Organisms are rubbed onto a dry PYR disk, incubated for 2 minutes, and then treated with detector reagent. A red color is positive.
Development of a bright cherry-red color within 1 minute after adding the detector reagent. PYR was hydrolyzed to β-naphthylamine.
No color change or a faint yellow/orange hue on the disk after adding the detector reagent. The organism is PYR-negative.
Development of a bright cherry-red color within 1 minute after adding the detector reagent. PYR was hydrolyzed to β-naphthylamine.
No color change or a faint yellow/orange hue on the disk after adding the detector reagent. The organism is PYR-negative.
What to look for
| Visual clue | Meaning | Student shorthand |
|---|---|---|
| Bright red/pink color | β-naphthylamine reacted with the N,N-dimethylaminocinnamaldehyde reagent | Positive for PYRase |
| No color change / orange color | Substrate remained unhydrolyzed; orange color is simply the reagent's natural color | Negative reaction |
| 2-minute incubation | The slide must incubate dry for 2 minutes before the drop of developer reagent is added | Method constraint |
PYR Interpretive Matrix
| Pattern | What to call it | How to think about it |
|---|---|---|
| Bright red color within 1 min | Positive | Organism produces L-pyrrolidonyl arylamidase. Presumptive S. pyogenes or Enterococcus. |
| Colorless, cream, or orange | Negative | Organism lacks L-pyrrolidonyl arylamidase. Presumptive Streptococcus agalactiae (Group B). |
- The PYR test detects L-pyrrolidonyl arylamidase, which cleaves the L-pyrrolidonyl-β-naphthylamide substrate.
- A positive result is a vibrant cherry red/pink spot forming on the white disk.
- This is one of the most reliable tests for presumptive identification of Group A Strep and Enterococci.
PYR positive = Streptococcus pyogenes (Group A) and Enterococcus. PYR negative = Streptococcus agalactiae (Group B). Red = Positive.