Exercise 5-4 Micro Lab: Methyl Red and Voges-Proskauer Tests
Methyl Red and Voges-Proskauer Broth
solution containing only peptone, glucose, and a phosphate buffer
Peptone and glucose provide protein and carbohydrate and the potassium phosphate resists pH changes in the medium
MR test
designed to detect organisms capable of performing mixed acid fermentation which overcomes the phosphate buffer in medium and lowers the pH
Mixed acid fermentation is verified by
the addition of methyl red indicator dye following incubation
Methyl red is ____ at a pH of 4.4 and ______ at a pH of .2. Between these two pH values, it is shades of _____
red
yellow
orange
_______ is the only true indication of a positive result. ____ is negative or inconclusive and __ is negative
red color
orange
yellow
the Voges-Proskauer test was designed for
for organisms that were able to ferment glucose but quickly convert their acid products to acetoin and 2,3 butanedoil
adding VP reagents to the medium does what?
oxidizes the acetoin to diacetyl,which in turn reacts with guanidine nuclei from peptone to produce red color