PYR Broth is recommended for isolation and identification of Streptococcus pyogenes based on PYR hydrolysis. PYR hydrolysis is a presumptive test for both group A and group D enterococcal streptococci. The PYR test determines the activity of enzyme L-pyrrolidonyl arylamidase (PYR) produced by Streptococcus pyogenes but not by other ß-haemolytic streptococci. Chromogenic mixture in the medium provides substrate for PYR enzyme.The PYR reagent when added reacts with ß-naphthylamine to form a red coloured Schiffs Base indicating a positive reaction.