PYR is a rapid colorimetric method for presumptive identification of certain groups of bacteria based on the activity of the enzyme pyrolidonyl arylamidase. L-pyroglutamic acid beta-naphthylamide is impregnated into the test disk and serves as the substrate for the detection of pyrolidonyl arylamidase. Hydrolysis of the substrate yields beta-naphthylamide which combines with the PYR Reagent (p-dimethylamino-cinnamaldehyde) to form a bright pink to cherry red color. A positive PYR tests allows for the presumptive identification of group A streptococci (Streptococcus pyogenes) and enterococci. In addition, investigators have determined that PYR activity is a key test for differentiation of some species of coagulase-negative Staphylococcus and for some genera of the family Enterobacteriaceae.
Organisms expected to give a positive result:
Principle:
Filter paper disks are impregnated with L-pyrrolidonyl-β- naphthylamide (PYR) which serves as a substrate for the detection of pyrrolidonyl arylamidase (PYRase). Following hydrolysis of the substrate by the enzyme, the resulting beta-naphthylamine produces a red color upon the addition of p- dimethylaminocinnamaldehyde (Color Developer).
Procedure:
- Using forceps, place the disk on a clean slide moisten slightly with 5-10µl of de-mineralized water using a loop or pipet.
- Pick up colonies and rub the inoculum gently into the small area of the disk.
- Incubate at room temperature for 2 minutes.
- Add 1 drop of color developer to the disk.
- Allow up to 1 minute for color change.
Interpretation:
A bright pink or cherry red color will appear within one minute if the test is positive. A negative test is indicated by no color change. The development of an orange, salmon, or yellow color should be interpreted as a negative reaction.Organisms expected to give a positive result:
- Group A streptococci (Streptococcus pyogenes)
- Group D enterococci (Enterococcus spp.)
- Coagulase-negative Staphylococcus spp.: haemolyticus, lugdunensis and schleiferi
- Citrobacter, Klebsiella, Yersinia, Enterobacter and Serratia spp.
A new PYR test is available which does not require a color developer. Simply apply the bacterial growth onto a strip with a loop and a positive test is indicated by the development of blue color in 1-2 minutes. This test does not use a color developer reagent. The conventional color developer reagent uses DMACA which should be used very carefully because it is carcinogenic.
ReplyDeleteThe new PYR is made by Biorex Labs in the United states.
Like One-Step PYR Test (Pyrrolidonyl Arylamidase), a One-Step LAP test (Leucine aminopeptidase) is also available from Biorex Labs in the United States. This test also does not require a color developer reagent. Simply apply the culture onto the XeroStrip and a grayish blue color indicates a positive test within 1-2 minutes.
ReplyDeletegroup d enterococci? or group d streptococci?
ReplyDelete