PYR Broth

PYR Broth is used for the isolation and identification of Streptococcus pyogenes .

Composition**

Final pH ( at 25°C) 7.8±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 37 grams in 1000 ml distilled water. Heat if necessary to dissolve the medium completely. Mix well and dispense as desired. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

Principle And Interpretation

PYR hydrolysis is a presumptive test for both group A and group D enterococcal streptococci (1). The PYR test determines the activity of enzyme L-pyrrolidonyl arylamidase (PYR) produced by Streptococcus pyogenes but not by other b-haemolytic streptococci (2). Free b-napthylamide is then detected by addition of the diazo dye complex, N ,N-dimethylaminocinnamaldehyde. Development of a red colour is indicative of PYR hydrolysis (3). PYR test is a highly sensitive test, which replaces bacitracin and salt tolerance (growth in 6.5% NaCl) tests (1). PYR Broth is recommended for detection and presumptive identification of S. pyogenes based on PYR hydrolysis (4).

Todd Hewitt Broth Base (M313) acts as the basal medium to which substrate for PYR enzyme is added (3).

Beef heart infusion and peptic digest of animal tissue provide nitrogenous nutrients. Dextrose is the carbohydrate serving as an energy source. Disodium phosphate serves as buffering agent and sodium chloride maintains osmotic balance. Chromogenic mixture provides substrate for PYR enzyme. After an incubation at 35-37°C for 18-24 hours, add 1 drop of PYR reagent (R043) directly to suspected surface growth on plate. Observe for colour change after 2 minutes. The chromogenic mixture is hydrolysed by S. pyogenes to L-pyrrolidone and b-naphthylamine. The PYR reagent reacts with b-naphthylamine to form a red coloured Schiffs Base indicating a positive reaction.

Quality Control

Appearance Cream to yellow homogeneous free flowing powder

Colour and Clarity of prepared medium Light yellow coloured clear solution

Reaction Reaction of 3.7% w/v aqueous solution at 25°C. pH : 7.8±0.2

pH 7.60-8.00

Cultural Response

M1789: Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.

Storage and Shelf Life

Store dehydrated and prepared medium at 2 - 8°C in tightly closed container. Use before expiry date on the label.

Reference

1. Facklam R. R., Thacker L. G, Fox B., Eriquez L., 1982, J. Clin. Microbiol., 15 (6), a, 987-990.
2. MacFaddin J. F., 2000, Biochemical Tests for Identification of Medical Bacteria, 3rd Edition, Lippinocott Williams and Wilkins, N.Y. 407-410.
3. Koneman E. W., Allen S. D., Janda W. M., Schreckenberger P. C., Winn W. C. Jr., 1992, Colour Atlas and Textbook of Diagnostic Microbiology, 4th Ed., J. B. Lippinccott Company.
4. Murray P. R., Baron J. H., Pfaller M. A., Jorgensen J. H. and Yolken R. H., (Eds.), 2003, Manual of Clinical Microbiology, 8th Ed., American Society for Microbiology, Washington, D.C.