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Ch. 3 - Observing Microorganisms Through a Microscope
Tortora - Microbiology: An Introduction 14th Edition
Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Tortora 14th EditionCh. 3 - Observing Microorganisms Through a Microscope문제 7
3장, 문제 7

What is the purpose of a counterstain in the acid-fast stain?

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1
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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주요 개념

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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.
추천 영상:
02:10
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.
추천 영상:
04:57
Gram Stain

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.
추천 영상:
03:44
Acids
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Why is a mordant used in the Gram stain? In the flagella stain?

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교과서 질문

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

1773
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교과서 질문

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

1607
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교과서 질문

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.

1454
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교과서 질문

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

1649
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교과서 질문

What is the purpose of a decolorizer in the Gram stain? In the acid-fast stain?

1844
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