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?
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Ch. 18 - Practical Applications of Immunology
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398
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Table of contents
- Ch. 1 - The Microbial World and You18
- Ch. 2 - Chemical Principles20
- Ch. 3 - Observing Microorganisms Through a Microscope18
- Ch. 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells21
- Ch. 5 - Microbial Metabolism20
- Ch. 6 - Microbial Growth20
- Ch. 7 - The Control of Microbial Growth20
- Ch. 8 - Microbial Genetics19
- Ch. 9 - Biotechnology & DNA Technology20
- Ch. 10 - Classification of Microorganisms15
- Ch. 11 - The Prokaryotes: Domains Bacteria and Archaea14
- Ch. 12 - The Eukaryotes: Fungi, Algae, Protozoa, and Helminths17
- Ch. 13 - Viruses, Viroids, and Prions20
- Ch. 14 - Principles of Disease and Epidemiology21
- Ch. 15 - Microbial Mechanisms of Pathogenicity19
- Ch. 16 - Innate Immunity: Nonspecific Defenses of the Host20
- Ch. 17 - Adaptive Immunity: Specific Defenses of the Host20
- Ch. 18 - Practical Applications of Immunology20
- Ch. 19 - Disorders Associated with the Immune System19
- Ch. 20 - Antimicrobial Drugs19
- Ch. 21 - Microbial Diseases of the Skin and Eyes21
- Ch. 22 - Microbial Diseases of the Nervous System19
- Ch. 23 - Microbial Diseases of the Cardiovascular and Lymphatic Systems20
- Ch. 24 - Microbial Diseases of the Respiratory System20
- Ch. 25 - Microbial Diseases of the Digestive System20
- Ch. 26 - Microbial Diseases of the Urinary and Reproductive Systems19
- Ch. 27 - Environmental Microbiology20
- Ch. 28 - Applied and Industrial Microbiology19
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook
Chapter 18, Problem 6
In an immunodiffusion test, a strip of filter paper containing diphtheria antitoxin is placed on a solid culture medium. Then bacteria are streaked perpendicular to the filter paper. If the bacteria are toxigenic,
a. The filter paper will turn red
b. A line of antigen–antibody precipitate will form
c. The cells will lyse
d. The cells will fluoresce
e. None of the above
Verified step by step guidance1
Understand the principle of immunodiffusion tests: these tests detect the formation of antigen-antibody complexes by diffusion of antigens and antibodies in a gel or solid medium.
Recognize that diphtheria antitoxin contains antibodies specific to diphtheria toxin (the antigen). When toxigenic bacteria produce diphtheria toxin, this antigen diffuses into the medium.
As the diphtheria toxin (antigen) diffuses from the bacteria and the antitoxin (antibody) diffuses from the filter paper, they meet in the medium and form an antigen-antibody complex.
The formation of this complex results in a visible precipitate line in the medium, indicating a positive reaction for toxigenic bacteria.
Therefore, the expected observation is the formation of a line of antigen–antibody precipitate, corresponding to option b.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Immunodiffusion Test
Immunodiffusion is a laboratory technique used to detect the presence of specific antigens or antibodies by their diffusion through a gel, forming a visible precipitate where they meet and react. It helps identify antigen-antibody interactions based on the formation of a precipitin line.
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Antigen–Antibody Precipitation
When an antigen and its specific antibody diffuse toward each other in a gel, they form a stable complex that precipitates out of solution, creating a visible line. This precipitate indicates a positive reaction, confirming the presence of the antigen or antibody.
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Toxigenic Bacteria and Diphtheria Antitoxin
Toxigenic bacteria produce toxins that can be neutralized by specific antitoxins. In the test, diphtheria antitoxin on the filter paper reacts with diphtheria toxin secreted by toxigenic bacteria, leading to antigen-antibody precipitation if the bacteria produce the toxin.
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Related Practice
Textbook Question
Label components of the direct and indirect ELISA tests in the following situations. Which test is direct? Which test provides definitive proof of disease?
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Textbook Question
Test used to identify rabies virus in the brain of a dog.
a. Direct fluorescent antibody
b. Indirect fluorescent antibody
c. Rabies immune globulin
d. Killed rabies virus
e. None of the above
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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?
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Textbook Question
Use the following choices to answer questions 7–9.
a. Direct fluorescent antibody
b. Indirect fluorescent antibody
c. Rabies immune globulin
d. Killed rabies virus
e. None of the above
Treatment given to a person bitten by a rabid bat.
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Textbook Question
How does the antigen in an agglutination reaction differ from that in a precipitation reaction?
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