The PYR tests can help to distinguish various species of Streptococci.
PYR refers to the first 3 letters of L-pyrrolidonyl-beta-naphthylamide
Hydrolysis of PYR indicates the presence of a specific aminopeptidase.
Reaction:
(1) Hydrolysis of PYR releases beta-naphthylamide.
(2) Addition of N,N-dimethylaminocinnamaldehyde reacts with the beta-naphthylamide to form a red Schiff base.
Colony selection: Gram-positive cocci, catalase negative (presumptive Streptococcal species)
Reading time: within 1 minute for broth method
Color
Interpretation
Species
red
positive
Streptococcus pyogenes (Group A beta-hemolytic); Enterococcus faecalis
yellow or orange
negative
other Streptococcal species
False positive:
(1) non-streptococcal organism
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Specialty: Clinical Laboratory, Infectious Diseases
