3.4.4: Methyl Red (MR) and Voges-Proskauer (VP) Test Activity

 

In this activity you will test two bacterial samples. Label each MRVP broth tube with the sample it is to be inoculated with.

1. Turn on the Bunsen burner and sterilize the inoculating loop by passing it through the flame of the burner.
2. Obtain a bacterial culture. Remove the cap. Pass the mouth of the tube through the flame of the Bunsen burner.
3. Insert the loop into the tube to acquire a sample of the bacterium.
4. Pass the tube through the flame of the Bunsen burner and recap the test tube, and return the tube to the test tube rack.
5. Pick up the MRVP broth tube to which the sample is to be transferred. Remove the cap and pass the mouth of the tube through the flame of the Bunsen burner.
6. Insert the loop into the tube to introduce the bacterial sample to the media.
7. Pass the mouth of the MRVP broth tube through the flame and recap it, and return it to the test tube rack.
8. Sterilize the inoculating loop by flaming the loop in the flame of the Bunsen burner.

Repeat steps 1 - 8 for the second bacterial species and MRVP broth tube to be inoculated.

9. Incubate the inoculated MRVP broth tubes at 37°C for 48 hours.
10. At 48 hours transfer 2.5 mL of each broth to new labeled sterile culture tubes. Methyl Red test:
11. To each of the new culture tubes add 5 drops of the methyl red reagent and then observe the color for the methyl red test and record your results.

Voges-Proskauer test:

12. In the remaining 2.5 ml of each culture add 0.6 mL of Barritt’s reagent A and 0.2 ml of Barritt’s reagent B. Shake the tube for 30 seconds to 1 minute. Wait 30 minutes and then observe the color of each tube and record your results.

In the table below write the name of the species tested and the results for each of the tests performed.

Experimental Results

Bacterial Species	Color after methyl red reagent	Methyl Red Test Results	Color after Barritt’s Reagents A & B	Voges-Proskauer Test Results

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