Download Methyl Red test

‫عمل الطالبة‪ :‬فداء علي نايف الجبور‬
‫الرقم الجامعي‪220053519:‬‬
‫التخصص‪ :‬تحاليل طبية‬
‫بإشراف كل من ‪:‬‬
‫د‪.‬عبد الرؤوف المناعمة‬
‫أ‪.‬نضال فياض‬
THE METHYL TEST(MR)
introduction
Methyl Red, also called Acid Red 2, is an
indicator dye that turns red in acidic solutions. It is
a dark red crystalline powder.
below pH 4.4
above pH 6.2
4.4
6.2
Methyl red is a pH indicator; it is red in pH under
4.4, yellow in pH over 6.2,
The principle of the test
Principle - To test the ability of an organism to
produce and maintain stable acid end products
from glucose fermentation.
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.
The equalation
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 SIGNIFICANCE
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.
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.
The type of bacteria which use in
this test…
.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,.
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 negative MR
result.
The result
red
MR positive (+)
yellow
MR negative (-)