عمل الطالبة : فداء علي نايف الجبور الرقم الجامعي : التخصص : تحاليل طبية بإشراف كل من : د. عبد الرؤوف المناعمة أ. نضال فياض

THE METHYL TEST(MR)

Methyl Red, also called Acid Red 2, is an indicator dye that turns red in acidic solutions. It is a dark red crystalline powder. indicatoracidic Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2,pH indicator introduction above pH 6.2 below pH

In micro biology, methyl red is used in the Methyl Red (MR) Test, used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation of glucose.Methyl Red (MR) Testbacteriafermentationglucose The principle of the test Principle - To test the ability of an organism to produce and maintain stable acid end products from glucose fermentation.

Different bacteria convert dextrose and glucose to pyruvate using different metabolic pathways. Some of these pathways produce unstable acidic products which quickly convert to neutral compounds. Other organisms use the mixed acid pathway, which produces acidic end products such as lactic, acetic, and formic acid. These acidic end products are stable and will remain acidic. The equalation

The Methyl Red test involves adding the pH indicator methyl red. If the organism uses the mixed acid fermentation pathway and produces stable acidic end-products, the acids will overcome the buffers in the medium and produce an acidic environment in the medium. When methyl red is added, if acidic end products are present, the methyl red will stay red. The SIGNIFICANCE

NOTE : # Methyl red differs from phenol red (which is used in the fermentation test) in that it is yellow at pH 6.2 and above and red at pH 4.4 and below. Phenol red turns yellow below a pH of 6.8. If you get these two pH indicators confused, you will have a difficult time to get results ## The MR tests are particularly useful in the identification of the Enterobacteriaceae ### and used to differentiate between ceratain bacteria called coil forms E.COIL

The procedure of test 1-Inoculate one broth using aseptic technique. Leave the other broth uninoculated (this will be a control). 2-Inoculate buffered glucose broth and incubate at 37°C for 48 hours 3-Obtain two MR-VP broths from the back shelf. 4-Incubate at appropriate temperature (whatever temperature your organism grows well at). Incubate for two to five days. 5-Obtain your broths from the incubator. 6-Add a few drops of Methyl Red to each broth culture. Methyl Red is found in small dropper bottles on the back shelf. 7-Observe the color (which should develop within a few minutes.buffered glucose broth

.Escherichia coli and Enterobacter cloacae. ** After incubation, you would perform an MR test on one tube of Escherichia coli and one tube of Enterobacter cloacae,. The type of bacteria which use in this test …

When methyl red is added to MR broth that has been inoculated with Escherichia coli, it stays red. This is a positive result for the MR test. When methyl red is added to MR-VP broth that has been inoculated with Enterobacter cloacae, it turns yellow. This is a negative MR result.

The result Escherichia coli, it stays red. This is a positive result for the MR test. Enterobacter cloacae, it stay yellow. This is a n nn negative MR result.

MR positive (+) red MR negative (-) yellow The result