Methyl Red - Voges Proskauer Test (MR-VP)

What is tested in this media?

To differentiate enteric bacterial species based on fermentation pathway is used to metabolize glucose

What are 2 test in this medium?

1. MR test → glucose fermentation via mixed acid fermentation pathway

2. VP test → glucose fermentation via 2,3-butanediol pathway

What are components of MR-VP medium?

• Pancreatic Digest of Casein

• Peptic Digest of Animal Tissue

• Potassium Phosphate

• Glucose

What is the purpose of potassium phosphate in MR-VP medium?

buffer

What is the purpose of glucose in MR-VP medium?

Fermentable sugar source

What is the color of Methyl Red in acidic condition?

Red

What is the color of Methyl Red in basic conditions?

Yellow

What is the positive result in Methyl Red test?

Red coloration of the incubated tube

What is the negative result in Methyl Red test?

Orange or yellow coloration

How do Voges-Proskauer test for specific glucose fermentation pathway that produces acetoin and 2,3-butanediol?

VP reagents A and B are added after incubation

Oxidize acetoin to diacetyl, which reacts with guanidine from peptone to produce a red color

What is the negative result of VP after addition of VP reagents A and B?

Color change to yellow or no color change

What is the positive result of VP after addition of VP reagents A and B?

Red color change

Brief protocol of Methyl Red- Voges Proskrauer?

Day 1:

1. Obtain 2 MR-VP tubes, label ( E.coli & A.faecalis)

2. Aseptically transfer bacteria to labeled tubes

3. Incubate for 48 hours

4. Record results

Day 2:

1. Vortex each tube, transfer 1mL to new test tubes

2. Add 5 drops of VP reagents A and B each

3. Observer color change