Q: Which of the following reactions is catalyzed by ornithine decarboxylase?

$$\text{Ornithine} \xrightarrow{\text{ornithine decarboxylase}} \text{Putrescine} + CO_2$

Question 1

Which chemical reaction is responsible for the formation of a peptide bond between two amino acids?

Accepted Answer

Dehydration synthesis reaction

Question 2

A microbiologist performs a gelatinase test and observes that after refrigeration, the gelatin medium remains liquid. What does this indicate about the bacterium?

Accepted Answer

The bacterium produces gelatinase, which hydrolyzes gelatin.

Question 3

Which of the following best describes the result of a positive urease hydrolysis test?

Accepted Answer

The medium turns bright pink due to the production of ammonia, increasing the pH.

Question 4

Which equation correctly represents the hydrolysis of urea by urease?

Accepted Answer

$$(NH_2$)_2CO + H_2O \rightarrow CO_2$ + 2NH_3$$

Question 5

A litmus milk test tube turns pink after incubation. What does this result indicate?

Accepted Answer

Lactose fermentation has occurred, producing acid.

Question 6

Which of the following bacteria is most likely to give a positive result for both the gelatinase and phenylalanine deamination tests?

Accepted Answer

Proteus vulgaris

Question 7

In the phenylalanine deamination test, what color change indicates a positive result after adding ferric chloride?

Accepted Answer

Green

Question 8

Which metabolic process is described by the removal of an amino group from an amino acid, resulting in the production of ammonia and an organic acid?

Accepted Answer

Deamination

Question 9

A bacterium is inoculated into ornithine decarboxylase medium. After incubation, the medium turns purple. What does this indicate?

Accepted Answer

The bacterium produces ornithine decarboxylase, resulting in an alkaline reaction.

Question 10

Which of the following is a correct interpretation of the MIO test if the tube shows diffuse growth, a red layer after Kovac’s reagent, and a purple medium?

Accepted Answer

Motile, indole positive, ornithine decarboxylase positive

Question 11

Which of the following best explains why the urease test is important in clinical microbiology?

Accepted Answer

It rapidly distinguishes Proteus species from other Enterobacteriaceae and helps diagnose H. pylori infections.

Question 12

Which of the following reactions is catalyzed by ornithine decarboxylase?

Accepted Answer

$$	ext{Ornithine} \xrightarrow{	ext{ornithine decarboxylase}} 	ext{Putrescine} + CO_2$

Question 13

A litmus milk tube becomes clear after incubation. What metabolic process has occurred?

Accepted Answer

Peptonization (casein hydrolysis)

Question 14

Which of the following organisms is most likely to be urease positive and cause alkaline urine leading to kidney stones?

Accepted Answer

Proteus mirabilis

Question 15

In the MIO test, which result would you expect for Escherichia coli?

Accepted Answer

Motile, indole positive, ornithine decarboxylase positive

Question 16

Which of the following best describes the role of exoenzymes in protein catabolism tests such as the gelatinase test?

Accepted Answer

They hydrolyze large extracellular proteins into smaller peptides and amino acids.

Question 17

A student observes a litmus milk tube with a purple color after incubation. What does this indicate?

Accepted Answer

Alkaline reaction due to amino acid catabolism

Question 18

Which of the following is a correct interpretation of a negative phenylalanine deamination test?

Accepted Answer

No green color develops after adding ferric chloride, indicating no phenylpyruvic acid was produced.

Question 19

Which of the following best explains why a control tube is used in the gelatinase test?

Accepted Answer

To confirm that solidification is due to the absence of gelatinase activity and not temperature alone.

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