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5.4: Review Questions

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    1. Why do you think it is important to do spot-inoculations for the amylase test and the caseinase test?

    2. What happens if you drop H2O2 into a cut on your arm? What does this tell you about the type of enzymes your cells might produce?

    3. (a) You inoculate an organism into phenol red lactose broth. The organism ferments lactose.

    What color is the medium? __________

    What does this tell you about the pH of the medium? __________________

    (b) The organism ferments lactose and produces gases.

    What do you use to detect gas production? ___________________?

    What do you see that indicates that gases are produced? ____________

    4. In what test is Kovac’s reagent used? __________________

    What molecule does Kovac’s reagent detect? ______________________________________

    To do this test, why do you have to grow the organism in medium containing tryptophan?

    5. In the urea test, what happens to the pH of the medium when an organism breaks down urea? What molecule causes this pH change?

    6. After inoculating a tube of nutrient gelatin, you incubate it overnight at 37° C. When you remove the tube from the incubator, you notice that the gelatin has liquefied. Does this indicate that the organism produces gelatinase? Why or why not?

    7. Fill in the following table to summarize the metabolic tests that you learned about .

    Test Biochemical reaction/ Enzyme involved Medium used/Inoculation Procedure Appearance of Result: Positive Result Apprearance of Result: Negative Result What causes the change in the medium’s appearance? (e.g. pH change, enzyme activity, etc.)
    Lactose Fermentation
    Citrate Permease (Simmon’s citrate test)
    Tryptophanase (Indole test)

    Results for Metabolic Tests:

    Bacteria Gram stain Morph-ology Arrang-ement Lactose Fermen-tation Gelat-inase Amylase Urease Citrate permease (Simmon’s citrate) Catalase Tryptophanase (Indole test)
    Bacillus subtilis
    Coryneb-acterium xerosis
    Enterob-acter aerogenes
    Escherichia coli
    Micrococcus luteus

    Pseudo-monas aeruginosa

    Proteus vulgaris
    Staphylo-coccus aureus
    Strepto-coccus faecalis
    Serratia marcescens

    The tests in the table above will be available for your practical exam. Use your results from Lab 5 to fill out this table. Results for the bacteria that were not tested in Lab 5 can be found on the Microbiology Review site on Blackboard.

    This page titled 5.4: Review Questions is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Joan Petersen & Susan McLaughlin.

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