Textbook Question
Why is a mordant used in the Gram stain? In the flagella stain?
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Ch. 3 - Observing Microorganisms Through a Microscope
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 3, Problem 7
What is the purpose of a counterstain in the acid-fast stain?
Verified step by step guidance1
Understand that the acid-fast stain is a differential staining technique used to identify acid-fast bacteria, such as Mycobacterium species, which have waxy cell walls resistant to decolorization by acid-alcohol.
Recognize that during the acid-fast staining process, the primary stain (usually carbol fuchsin) penetrates all cells, staining them red or pink.
After applying acid-alcohol, non-acid-fast cells lose the primary stain because their cell walls do not retain it, becoming colorless at this stage.
The counterstain (commonly methylene blue or brilliant green) is then applied to stain the decolorized non-acid-fast cells, providing a contrasting color to the acid-fast cells.
Therefore, the purpose of the counterstain is to provide a visible color to non-acid-fast bacteria, allowing differentiation between acid-fast (red/pink) and non-acid-fast (blue/green) cells under the microscope.
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Key Concepts
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Acid-Fast Stain Technique
The acid-fast stain is a differential staining method used to identify acid-fast bacteria, such as Mycobacterium species, which have waxy cell walls resistant to decolorization by acid-alcohol. This technique involves primary staining, decolorization, and counterstaining steps to differentiate acid-fast from non-acid-fast cells.
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Introduction to Staining
Role of Counterstain in Staining Procedures
A counterstain is applied after decolorization to provide contrast by staining cells that did not retain the primary stain. In the acid-fast stain, the counterstain colors non-acid-fast bacteria, making them visible and distinguishable from acid-fast bacteria under the microscope.
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Differentiation of Acid-Fast and Non-Acid-Fast Bacteria
The acid-fast stain differentiates bacteria based on cell wall composition; acid-fast bacteria retain the primary stain (carbol fuchsin) and appear red, while non-acid-fast bacteria lose the primary stain during decolorization and take up the counterstain (usually methylene blue), appearing blue.
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Related Practice
Textbook Question
Which of the following pairs is mismatched?
a. Capsule—negative stain
b. Cell arrangement—simple stain
c. Cell size—negative stain
d. Gram stain—bacterial identification
e. None of the above
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Textbook Question
Assume that you are viewing a Gram-stained field of red cocci and blue rods through the microscope. You can safely conclude that you have
a. Made a mistake in staining
b. Two different species
c. Old bacterial cells
d. Young bacterial cells
e. None of the above
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Textbook Question
Which of the following is not a functionally analogous pair of stains?
a. Nigrosin and malachite green
b. Crystal violet and carbolfuchsin
c. Safranin and methylene blue
d. Ethanol-acetone and acid-alcohol
e. All of the above pairs are functionally analogous.
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Textbook Question
Assume you stain Clostridium by applying a basic stain, carbolfuchsin, with heat, decolorizing with acid-alcohol, and counterstaining with an acidic stain, nigrosin. Through the microscope, the endospores are 1, and the cells are stained 2.
a. 1—red; 2—black
b. 1—black; 2—colorless
c. 1—colorless; 2—black
d. 1—red; 2—colorless
e. 1—black; 2—red
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Textbook Question
What is the purpose of a decolorizer in the Gram stain? In the acid-fast stain?
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