Exercise 5: Acid Fast Stain and Endospore Stain
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27 Terms
What is the main purpose of an acid-fast stain?
To identify bacteria that are acid-fast.
What is the correct order of the acid-fast stain reagents?
Carbolfuchsin → acid-alcohol → methylene blue.
What color are acid-fast bacteria after an acid-fast stain?
Red.
What color are non-acid-fastbacteria after an acid-fast stain?
Blue.
What is the primary stain used in an acid-fast stain?
Carbolfuchsin.
What is the decolorizer used in an acid-fast stain?
Acid-alcohol.
What is the counterstain used in an acid-fast stain?
Methylene blue.
What is the main purpose of an endospore stain?
To identify endospores in bacterial cells.
What is the correct order of the endospore stain reagents?
Malachite green → water → safranin.
What is the primary stain used in an endospore stain?
Malachite green.
What is the counterstain used in an endospore stain?
Safranin.
What color are endospores after an endospore stain?
Green.
What color are vegetative bacterial cells after an endospore stain?
Red or pink.
Why is heat used during an endospore stain?
To help malachite green penetrate the endospore.
Which bacterium is used as the known endospore-forming organism?
Bacillus cereus Clostridioides difficile
Which bacterium is used as the known acid-fast organism?
Mycobacterium smegmatis Mycobacterium tuberculosis
Which bacterium is used as the known non-acid-fast organism?
Micrococcus luteus.
Which bacterial genus lacks a cell wall?
Mycoplasma.
What makes Mycobacterium acid-fast?
The waxy mycolic acid layer in its cell wall.
In an Acid-Fast Stain, what color do Acid-Fast Bacteria appear, and why?
They appear bright red/pink (magenta). Their waxy cell walls, rich in mycolic acid,
In an Acid-Fast Stain, what color do Non-Acid-Fast Bacteria appear, and why?
They appear blue (or light blue). Lacking high concentrations of waxy mycolic acids, their cell walls are rapidly decolorized by acid-alcohol and subsequently absorb the counterstain (methylene blue).
In an Endospore Stain (Schaeffer-Fulton method), what color do Endospores appear, and why?
They appear green (elliptical or spherical structures). The primary stain, malachite green, is forced into the highly resistant, keratin-rich spore coat using heat/steam and resists subsequent water decolorization
In an Endospore Stain, what color do Vegetative Cells appear, and why?
They appear pink/red. After the decolorization step, the vegetative cells, which do not retain the primary stain, absorb the counterstain (safranin) and take on a pink hue.
What is the main purpose of an acid-fast stain?
To identify bacteria that are acid-fast.
What is the correct order of the acid-fast stain reagents?
Carbolfuchsin → acid-alcohol → methylene blue.
What color are acid-fast bacteria after an acid-fast stain?
Red.
What color are non-acid-fast bacteria after an acid-fast stain?
Blue.