MR-VP Reactions Pg.91-94 ( Not Done/still Need Some Results) Flashcards
MR-VP is an acronym for two separate tests:
Methyl Red and Vogues-Proskauer
These two tests are based on differences in:
Bacterial fermentative end products
The tests ere originally used to distinguish between:
Escherichia coli and Enterobacter aerogenes
These tests are now used to assist in the identification of many other species, primarily in:
The family Enterobacteriaceae
A single tube of broth medium containing ________ can be used for evaluation of both tests.
Glucose
Some bacteria (E. Coli) ferment the glucose and produce acids of such concentration and strength that the pH that the pH is lowered to ….
4.4 or less (MR test).
Other bacteria (E. Aerogenes) ferment the same carbohydrate and produce a neutral end product such as: ___________, detected in the V-P test.
Acetyl methyl carbinol (AMC)
Equation for methyl red test:
Enzyme pathway
Glucose————————->ATP+ Organic Acids
Equation for Voges-Proskauer test:
Enzyme Pathway
Glucose—————————> ATP+AMC+Organic Acids/Alcohols (Acetyl Methyl Carbinol)
Procedure: both tubes of E. Coli and E. Aerogenes are incubated at 37 degrees Celsius for how long?
2-3 days.
After incubation, in order to add the appropriate reagents required for each test, you will need to:
Aliquot each of the grown broth cultures into 2 separate clean test tubes.
How should the broth look after incubation?
Cloudy with growth
How may drops of methyl red indicator is added into the tube labeled MR?
5
What does a red color indicate?
The presence of a strong acid, pH 4.4 or lower, ex: organic acids.
What does a yellow color indicate?
A yellow, orange or gold color indicates the absence of strong acid pH 6.0 or higher.
For the Voges-Proskauer test, how many drops of VPA AND VPB are added to the VP tube?
8 drops each
How long should the sample stand after the drops are added in?
Minimum of 20-30min. Do not agitate the tube.
A ring or layer of what color at the top of the liquid indicates presence of AMC. What does any other color indicate?
RED COLOR
Any other color= negative reaction
Results for MR test:
Medium: MRVP broth
Substrate:glucose
Reagents: methyl red
Positive end prod: ATP & organic acid
Positive appearance:red
Negative appearance: yellow and orange
VP results:
Broth: MRVP broth
Substrate: glucose
Reagents: vp
POs. End prods.= ATP, organic acids, alcohol
POs. Appearance= dark red
Neg appearance= any color than red
E. Aerogenes was what color
Yellow, negative
E. Coli was what color
Red, positive
