Methyl Red and Voges-Proskauer Tests
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Can you use the same broth for Methyl red and Vogues-Proskauer tests?
Yes, you can
What is in the methyl red Voges-Proskauer broth?
peptone, glucose, and phosphate buffer
What is the methyl red test designed for?
Detect organism capable of mixed acid fermentation
What is mixed acid fermentation?
stable acid that can overcome the phosphate buffer in the broth and lower pH
How do you verify if there is indeed mixed acid fermented in the broth?
Adding methyl red to the tube after incubation. If the broth turn red, then the bacteria can be determine to ferment mix acid. Orange color mean inconclusive and yellow mean non mixed acid ferment
At what pH is methyl red turn red? Yellow? Orange
- pH 4.4=red
- pH 4.4-6.2=orange
- pH 6.2= yellow
What is the Voges-Proskauer test design for?
Detect organism that can ferment glucose, but quickly convert it to acetoin and 2,3-butanediol.
How would you detect acetoin produced?
By adding a VP reagent that would oxidize acetoin to diacetyl. this diacetyl reacted with guanidine nuclei from peptone to produce a red color
what does it mean if there is no color change or if there is a copper color on top after VP reagent was added?
The test is negative. No acetoin was produced
Where did the copper color come from?
reaction of KOH and alpha naphthol. Not positive for VP test
What is the Methyl Red and Vogues Proskauer test use for?
- It is the component of IMViC(Indole, Methyl red, Vogues-Proskauer, and Citrate).
- IMViC are tests to distinguish between member of Enterobacteriaceae and differentiate them from other Gram negative rod
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