Question 1

Which of the following best describes the purpose of the laboratory technique shown in the first image (96-well plate with clear wells)?

Accepted Answer

To perform an ELISA (Enzyme-Linked Immunosorbent Assay) for detecting the presence of specific antigens or antibodies.

Question 2

In the Kirby-Bauer disk diffusion method (as shown in the second image), which antibiotic disk would be considered the most effective against the tested bacterium?

Accepted Answer

The disk with the largest zone of inhibition.

Question 3

A Mueller-Hinton agar plate is inoculated with Escherichia coli and several antibiotic disks are placed on the surface. After incubation, which result indicates that E. coli is resistant to a particular antibiotic?

Accepted Answer

No clear zone, with bacterial growth up to the edge of the disk.

Question 4

Which of the following is a correct step in the ELISA procedure as demonstrated by the first image?

Accepted Answer

Adding a substrate that reacts with an enzyme to produce a color change.

Question 5

If you observe a 96-well plate after an ELISA and see that some wells have a color change while others remain clear, what does this indicate?

Accepted Answer

Only the wells with a color change are positive for the target antigen or antibody.

Question 6

Which of the following best explains why the Mueller-Hinton agar is used for the disk diffusion method?

Accepted Answer

It allows for consistent diffusion of antibiotics and supports the growth of most non-fastidious organisms.

Question 7

A student performs a Kirby-Bauer test and measures the following zones of inhibition: Antibiotic X = 20 mm, Antibiotic Y = 40 mm. Which antibiotic is more effective against the tested organism?

Accepted Answer

Antibiotic Y

Question 8

Which of the following is NOT a possible reason for a lack of zone of inhibition around an antibiotic disk in the Kirby-Bauer test?

Accepted Answer

The antibiotic is highly effective against the bacterium.

Question 9

In the context of the ELISA test, what is the function of the enzyme-linked secondary antibody?

Accepted Answer

It binds to the primary antibody and catalyzes a reaction with the substrate to produce a detectable signal.

Question 10

Which of the following best describes the order of binding events in a positive well of an indirect ELISA?

Accepted Answer

Antigen binds to the well, primary antibody binds to antigen, enzyme-linked secondary antibody binds to primary antibody, substrate is added.

Question 11

Which of the following equations correctly represents the calculation for the diameter of the zone of inhibition in the Kirby-Bauer test?

Accepted Answer

$$d = 2r$$

Question 12

Why is it important to use a standardized inoculum (e.g., 0.5 McFarland standard) when performing the Kirby-Bauer disk diffusion test?

Accepted Answer

To ensure consistent and reproducible results by controlling the density of bacterial growth.

MCB 2010 Final Exam Review: Microbiology Study Guidance

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