Question 1

Which of the following best describes the primary purpose of the API 20E test strip in microbiology?

Accepted Answer

To test for fermentation and other metabolic activities in Gram-negative rods

Question 2

During the API 20E procedure, why is it important to use a sterile inoculating loop when preparing the bacterial suspension?

Accepted Answer

To prevent contamination of the test strip and ensure accurate results

Question 3

A positive result in the ONPG test well of the API 20E strip indicates which of the following?

Accepted Answer

The organism produces β-galactosidase

Question 4

If the GLU well in the API 20E strip turns yellow, what does this indicate about the organism?

Accepted Answer

The organism ferments glucose

Question 5

Which equation would you use to calculate the concentration of bacteria in the suspension if you know the volume and the number of colonies formed after plating?

Accepted Answer

$$C = \frac{N}{V}$$

Question 6

A student observes a blue color in the CIT well of the API 20E strip. What does this result indicate?

Accepted Answer

The organism utilizes citrate as a carbon source

Question 7

Which of the following is a critical step in the API 20E procedure to ensure the accuracy of the test results?

Accepted Answer

Adding mineral oil to the anaerobic wells

Question 8

If an organism produces a red color in the VP well after the addition of reagents, what does this indicate?

Accepted Answer

The organism produces acetoin

Question 9

Which of the following tests on the API 20E strip is used to detect the production of indole?

Accepted Answer

IND

Question 10

A student incorrectly uses a contaminated loop to inoculate the API 20E strip. Which of the following is the most likely consequence?

Accepted Answer

False positive or negative results due to mixed cultures

Question 11

Which of the following best explains why mineral oil is added to certain wells in the API 20E strip?

Accepted Answer

To create anaerobic conditions for specific tests

Question 12

If the TDA well turns red after the addition of ferric chloride, what does this indicate?

Accepted Answer

The organism produces tryptophan deaminase

Question 13

Which of the following is a plausible reason for a false negative result in the API 20E test?

Accepted Answer

Insufficient bacterial suspension used for inoculation

Question 14

A positive result in the URE well of the API 20E strip is indicated by which color change?

Accepted Answer

Pink to red

Question 15

Which of the following best describes the interpretation of a blue color in the GEL well?

Accepted Answer

The organism produces gelatinase

Question 16

If an organism produces a blue color in the SAC well, what does this indicate?

Accepted Answer

The organism ferments saccharose

Question 17

Which of the following steps is necessary to ensure the correct interpretation of the API 20E test results?

Accepted Answer

Comparing the color changes in the wells to the reference chart

Question 18

A student observes a yellow color in the MAN well. What does this result indicate?

Accepted Answer

The organism ferments mannitol

Question 19

Which of the following is the correct formula for calculating the dilution factor when preparing a bacterial suspension for the API 20E test?

Accepted Answer

$$DF = \frac{V_{total}}{V_{sample}}$$

Question 20

Which of the following best describes the interpretation of a blue color in the LDC well?

Accepted Answer

The organism produces lysine decarboxylase

API 20E: Identification of Enterobacteriaceae and Other Gram-Negative Rods

Study Guide - Practice Questions

Study Guide - Flashcards