NAME AND COURSE SECTION: Michele McNeill, Camile Manradge – Section 704
TITLE AND NUMBER: Biochemical Testing of Microbes – Lab #6
Exercise #1: Methyl Red-Voges Proskauer Test
Exercise #2: Motility Testing
Exercise #3: Carbohydrate Fermentation Testing
PURPOSE: We will prepare an E. coli culture, and further explore and become familiar with differential staining techniques using the Gram stain. We will use Crystal Violet dye, Iodine, acetone-alcohol, and Safranin to stain cells and differentiate between Gram-negative and Gram-positive bacteria (S. epidermidis, L. acidophilus, S. cerevisiae, and E. coli). Is to identify organisms.
Pre-Experiment Preparation: ...view middle of the document...
coli and S. epidermidis cultures in the refrigerator for use in future experiments.
• We then mixed one tablespoon of bleach into the yeast and L. acidophilus cultures, let them sit for 30 minutes, and then discarded them.
A. Methyl Red Test Results
Both tubes were instantaneously red in color and had positive red bands on both of them.
B. Methyl Red Test Results
Next the instant red reaction to the reagent indicates a positive MR - VP test result. With this results prove that there is presence of acid from glucose. It was very interesting difference between the two test cultures was how far down the color penetrated. The E. coli was completely red, while the S. Epidermidis had a band of light liquid.
Voges Proskauer Test
The two remaining broth test tubes were primed for the MR-VP test with four (4) drops of Barritt's B reagent. Tubes were mixed gently after each addition for oxygen exposure for color to occur. The tubes required a half hour (30 minutes) before reading of results. While waiting for the results we encounter a small problem by getting the tubes to stay in place, but we managed somehow to make it work. We then sterilized the tubes in boiling water for future use.
The liquid in both tubes was diluted orange gradually. They both had pink bands at the top, but color indicates an inconclusive result, meaning there was a pH between 4.4 and 6.
Exercise, 1a. – Catalase Test
• We first disinfect our work area again with 10% bleach.
• We then labeled 2 microscope slides E.coli and Epidermidis.
• We then used a plastic inoculation to loop to transfer a sample of each organism to the matching slide.
• Then we added a drop of hydrogen peroxide to smear. We did mix it with the plastic loop.
The results showed no bubbles in S. Epidermis and only a few tiny, short lived bubbles in E. coli. According to the lab manual, this showed that there were two negative results.
Experiment #6 Exercise 1 and 2 - Methyl Red; Voges-Proskauer, and Catalase Test:
|Culture |Methyl Red, Ex.1 |Voges–Proskauer, Ex.1 |Catalase Test, Ex. 2 |
|E. coli |Positive, red. |Positive, red band present. |Negative, no bubbles. |
|S. epidermis |Positive, red. |Positive, red band present. |Negative, no bubbles. |
Experiment #6 Methyl Red; Voges-Proskauer, and Catalase Test:
A. What is meant by the term biochemical profile?
Biochemical profile is a variety of biochemical tests. These various tests are used to measure the constituents of plasma and serum in blood.
B. What metabolic end product does the MR test for?
The metabolic end product MR tests for are the different bacteria’s related to their...