Exercise 5-4 Micro Lab: Methyl Red and Voges-Proskauer Tests

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1

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

2

MR test

designed to detect organisms capable of performing mixed acid fermentation which overcomes the phosphate buffer in medium and lowers the pH

3

Mixed acid fermentation is verified by

the addition of methyl red indicator dye following incubation

4

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

5

_______ is the only true indication of a positive result. ____ is negative or inconclusive and __ is negative

red color
orange
yellow

6

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

7

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