Question 1

Which chemical reaction is catalyzed by the enzyme urease during the urease test?

Accepted Answer

Hydrolysis of urea to produce ammonia and carbon dioxide: $$\mathrm{(NH_2$)_2CO + H_2O \rightarrow 2NH_3 + CO_2$}$$

Question 2

A urine sample is inoculated onto urea agar and incubated. After 2 hours, the medium turns bright pink. What does this result indicate?

Accepted Answer

The organism rapidly hydrolyzes urea, producing ammonia and increasing the pH.

Question 3

Which of the following organisms is expected to give a slow positive urease test result, requiring 3 or more days for a color change?

Accepted Answer

Klebsiella pneumoniae

Question 4

What is the role of the pH indicator in the urease test?

Accepted Answer

It detects the increase in pH due to ammonia production, changing color from yellow/orange to pink.

Question 5

Why is the urease test result read within 24 hours in routine diagnostic laboratories?

Accepted Answer

To distinguish rapid urease producers from slow ones and avoid false positives due to prolonged incubation.

Question 6

A microbiologist observes a urea agar slant that remains yellow after 24 hours of incubation. Which organism is most likely present?

Accepted Answer

Escherichia coli

Question 7

Which of the following best explains why the medium becomes alkaline during a positive urease test?

Accepted Answer

Ammonia ($$NH_3) is $$produced, which increases the pH.

Question 8

A patient with a urinary tract infection has a urine culture that turns urea agar pink within 2 hours. Which organism is most likely responsible?

Accepted Answer

Proteus vulgaris

Question 9

Which of the following is NOT a plausible reason for a false negative urease test result?

Accepted Answer

The organism is a rapid urease producer.

Question 10

If a urea agar slant is inoculated with Klebsiella pneumoniae and incubated for 48 hours, what result is expected?

Accepted Answer

A slow positive result: the medium turns pink after more than 24 hours.

Question 11

Which equation correctly represents the hydrolysis of urea by urease?

Accepted Answer

$$\mathrm{(NH_2$)_2CO + H_2O \xrightarrow{urease} 2NH_3 + CO_2$}$$

Question 12

A laboratory technician mistakenly incubates a urea agar slant for 5 days before reading the result. What is the most likely consequence?

Accepted Answer

Slow urease producers may appear positive, making it difficult to distinguish them from rapid producers.

Question 13

Which of the following statements about Escherichia coli and the urease test is correct?

Accepted Answer

Escherichia coli is urease negative and does not change the color of urea agar.

Question 14

In the urease test, what is the significance of the color change from orange/yellow to pink?

Accepted Answer

It indicates an increase in pH due to ammonia production from urea hydrolysis.

Question 15

A clinical isolate is tested for urease activity. The urea agar slant turns pink after 72 hours. What does this result suggest?

Accepted Answer

The organism is a slow urease producer.

Question 16

Which of the following best describes the mechanism by which the urease test detects urease activity?

Accepted Answer

Urease hydrolyzes urea to produce ammonia, which raises the pH and causes the pH indicator to turn pink.

Question 17

A urea agar slant is inoculated with Proteus vulgaris. After 1 hour, the medium turns pink. What does this indicate about the organism?

Accepted Answer

Proteus vulgaris is a rapid urease producer.

Question 18

Which of the following is a common misconception about the urease test?

Accepted Answer

A pink color always appears immediately if the organism is urease positive.

Question 19

In a clinical setting, why is the urease test particularly useful for identifying Proteus species?

Accepted Answer

Proteus species are rapid urease producers, turning the medium pink within 1-2 hours.

Urease Test in Microbiology: Principle, Procedure, and Interpretation

Study Guide - Practice Questions