Skip to main content
Ch. 18 - Practical Applications of Immunology
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
All textbooksTortora 14th EditionCh. 18 - Practical Applications of ImmunologyProblem 4
Chapter 18, Problem 4

Use the following choices to answer questions 4 and 5:
a. Anti-Brucella
b. Brucella
c. Substrate for the enzyme
Which is the third step in a direct ELISA test?

Verified step by step guidance
1
Understand the principle of a direct ELISA test: it involves detecting an antigen immobilized on a surface using a labeled antibody specific to that antigen.
Recall the sequence of steps in a direct ELISA: first, the antigen (in this case, Brucella) is attached to the well surface.
Second, a labeled antibody (anti-Brucella) is added, which binds directly to the antigen.
Third, after washing away unbound antibodies, a substrate for the enzyme linked to the antibody is added to produce a detectable signal.
Therefore, identify the third step as the addition of the substrate for the enzyme to develop the signal.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Direct ELISA Procedure

Direct ELISA is an immunoassay technique used to detect the presence of an antigen in a sample. It involves immobilizing the antigen on a surface, then adding a labeled antibody that directly binds to the antigen. Understanding the sequence of steps—coating, blocking, antibody binding, and detection—is essential to identify the third step.
Recommended video:
Guided course
03:28
Direct Microscopic Cell Counts

Role of Antibodies in ELISA

Antibodies are proteins that specifically bind to antigens. In direct ELISA, a labeled antibody (such as anti-Brucella if detecting Brucella antigen) binds directly to the target antigen. Recognizing the function and specificity of antibodies helps clarify which reagent is added at each step.
Recommended video:
Guided course
00:48
Antibodies

Enzyme-Substrate Reaction in ELISA Detection

The enzyme linked to the antibody catalyzes a reaction with a substrate to produce a detectable signal, usually a color change. This step follows antibody binding and is crucial for visualizing the presence of the antigen. Knowing when the substrate is added helps determine the order of ELISA steps.
Recommended video:
Guided course
03:49
Enzyme-Substrate Complex
Related Practice
Textbook Question

Use the following choices to answer questions 4 and 5:

a. Anti-Brucella

b. Brucella

c. Substrate for the enzyme

Which item is from the patient in an indirect ELISA test?

832
views
Textbook Question

The examples in questions 1 and 2 are:

a. Direct tests

b. Indirect tests

1554
views
Textbook Question

How are monoclonal antibodies produced?

1727
views
Textbook Question

Explain the effects of excess antigen and antibody on the precipitation reaction. How is the precipitin ring test different from an immunodiffusion test?

1578
views
Textbook Question

Use the following choices to answer questions 1 and 2:

a. Hemolysis

b. Hemagglutination

c. Hemagglutination inhibition

d. No hemolysis

e. Precipitin ring forms

Patient’s serum, Chlamydia, guinea pig complement, sheep red blood cells, and anti-sheep red blood cells are mixed in a tube. What happens if the patient has antibodies against Chlamydia?

834
views
Textbook Question

Label the components of the direct and indirect FA tests in the following situations. Which test is direct? Which test provides definitive proof of disease?

1198
views