Lab quiz 6

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Define fermentations.

Energy-producing biochemical reactions in which organic molecules serve both as electron acceptors and donors

Why don't all microorganisms produce the same end product from pyruvate?

The end product is a characteristic of the particular microorganism

What is a Durham tube?

small, liquid fill, inverted tube

What is the purpose of a Durham tube?

It is used as a gas trap

What is the color of phenol red at an acid pH?

Yellow

What is the purpose of carbohydrate fermentation?

To see if glucose fermented to acids or acids and gas.

What is the importance of catalase to certain bacteria?

Some bacteria contain flavoproteins that reduse oxygen, resulting in production of hydrogen peroxide
-Hydrogen peroxide is toxic to the bacteria.
-Catalase catalyzes the destruction of hydrogen peroxide

Do anaerobic bacteria require oxygen?

No, because they contain flavoproteins that produce hydrogen peroxide

What is the substrate of the catalase reaction?

H2O2 (hydrogen peroxide)

What does a positive catalse reaction look like?

Bubbles form (This can be recorded immiedately)

What metabolic property characterizes bacteria that possess oxidase activity?

Cytochrome c oxidase

What is the importance of cytochrome oxidase to bacteria that possess it?

It uses oxygen as an electron acceptor during the oxidation of reduced cytochrome c to form water and oxidized cytochrome c.

Do anaerobic bacteria require oxidase?

No, because anaerobic bacteria do no require oxygen

What is the function of the test reagent in the oxidase test?

It produces a color change;
If black/blue color forms, you have a positive oxidase

The oxidase test is used to differentiate among which groups of bacteria?

The bacteria that use oxygen as the final electron acceptor and those that don't. (Anaerobic and Aerobic)

Why should nichrome or other iron-contatining inoculating devices not be used in the oxidase test?

May cause a false-positive reaction

Explain the biochemistry of the urease reaction.

Urease attacks the nitrogen and carbon bond in amide compounds such as urea, forming the end products CO2 and water.

What is the purpose of the phenol red in the urea broth or slant medium?

pH indicator

When would you use the urease test?

To see if urea can be used as a nitrogen source.

In a positive urease test, why does the urea broth or slant change color?

To show a positive test for urea hydrolysis

What is urea?

High concentration in urine; many UTI pathogens are urease positive

If NH3 formed pH inreases, pH colonies produce what color to show a positive urease?

Hot pink

Why is the development of a red color a negative test when zinc is added?

Since zinc reduces nitrates to nitrites, a pink or red color will appear and verifies the fact that nitrates were not reduced to nitrites by the bacteria (a negative test).

What is the purpose of Nitrate Reduction?

To identify anaerobic respiration

After reagents A&B are added for the nitrate reduction test, what happens?

Produce a red color: positive nitrate reduction
Colorless: either positive or negative nitrate reduction

To confirm, you add a pinch of zinc powder. What happens?

Produces a red color: Negative nitrate reduction
Remains colorless: Positive nitrate reduction

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