Question 1

Which of the following best describes the process of deamination in amino acid catabolism?

Accepted Answer

Removal of an amino group (NH$$_2) $$from an amino acid

Question 2

A microbiologist adds ferric chloride (FeCl$$_3) to a $$phenylalanine slant and observes a dark green color. What does this indicate about the organism?

Accepted Answer

The organism produces phenylalanine deaminase

Question 3

Which result would you expect if an organism is positive for hydrogen sulfide (H$$_2S) $$production in the peptone iron deep test?

Accepted Answer

A black precipitate forms along the stab line

Question 4

In the MIO tube, which combination of results would indicate that an organism is motile, produces indole, and decarboxylates ornithine?

Accepted Answer

Cloudy growth, cherry-red layer after Kovac's, and purple medium

Question 5

A student inoculates a peptone iron deep with an unknown bacterium. After incubation, there is no blackening along the stab line. What is the most likely interpretation?

Accepted Answer

The organism is negative for hydrogen sulfide (H$$_2S) $$production

Question 6

Which of the following best describes the purpose of adding Kovac's reagent to the MIO tube?

Accepted Answer

To detect the production of indole from tryptophan

Question 7

During a lab, a student observes that the MIO tube is purple throughout after incubation. What does this indicate about the organism?

Accepted Answer

The organism is positive for ornithine decarboxylase

Question 8

Which of the following is the correct sequence of steps for inoculating a phenylalanine slant?

Accepted Answer

Streak the surface back and forth in a zigzag pattern

Question 9

A microbiologist is testing for decarboxylation of ornithine. Which chemical group is removed during this reaction, and what is the byproduct?

Accepted Answer

Carboxyl group (COOH) is removed, releasing carbon dioxide (CO$$_2)$$

Question 10

Which of the following best explains why a black precipitate forms in the peptone iron deep when hydrogen sulfide (H$$_2S) is $$produced?

Accepted Answer

H$$_2S $$reacts with iron salts in the medium to form insoluble iron sulfide (FeS)

Question 11

A student forgets to add ferric chloride (FeCl$$_3) to $$the phenylalanine slant after incubation. What is the most likely consequence?

Accepted Answer

The test will not reveal a positive result, even if phenylalanine deaminase is present

Question 12

Which of the following organisms would you expect to be covered in the lab exercise based on the provided materials?

Accepted Answer

Proteus mirabilis

Question 13

If an MIO tube shows growth only along the stab line, no color change after adding Kovac's reagent, and the medium is yellow, what can you conclude?

Accepted Answer

The organism is non-motile, indole negative, and ornithine decarboxylase negative

Question 14

Why is it important to withdraw the inoculating needle along the same line after stabbing the MIO or peptone iron deep tubes?

Accepted Answer

To ensure accurate observation of motility and H$$_2S $$production along the stab line

Question 15

A clinical isolate is tested in a phenylalanine slant and shows no color change after adding FeCl$$_3. $$What is the most likely interpretation?

Accepted Answer

The organism is negative for phenylalanine deaminase

Question 16

Which of the following best describes the role of the phenylalanine deaminase test in clinical microbiology?

Accepted Answer

It identifies bacteria capable of removing the amino group from phenylalanine

Question 17

A patient sample is inoculated into an MIO tube. After incubation, the tube is cloudy throughout, a cherry-red layer forms after adding Kovac's reagent, and the medium is yellow. What is the correct interpretation?

Accepted Answer

Motile, indole positive, ornithine decarboxylase negative

Question 18

Which of the following best explains why the phenylalanine slant test requires the addition of FeCl$$_3$$ after incubation?

Accepted Answer

FeCl$$_3$$ reacts with phenylpyruvic acid, the product of phenylalanine deamination, to produce a green color

Question 19

A student is interpreting the results of a peptone iron deep test. Which chemical equation best represents the reaction leading to black precipitate formation?

Accepted Answer

$$\mathrm{H_2S + Fe$$^{2+}$$ \rightarrow FeS \downarrow + 2H^+}$$

Protein Catabolism II: Amino Acid Breakdown and Diagnostic Tests

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