Question

What molecule do the acid-fast bacteria have in their cell wall that “makes” them acid-fast? What dye is used to stain the cells that are positive in this reaction? What color would the positive cells stain?  What dye is used as the counterstain in this reaction? What color would the negative cells stain?

Answer 1

"The term aicd fast means that the microorganisms are resistant to decolorization by an acid"

What molecules do the acid-fast bacteria have in their cell wall that “makes” them acid-fast?

Answer: Acid fast bacteria (AFB) have a large amount of a specific glycolipid called mycolic acid in their cell wall that makes them acid fast.

What dye is used to stain the cells that are positive in this reaction?

Answer: Acid fast organisms require a special staining technique as their cell wall is resistant to most compounds.

So, a lipid solube compound carbolfuchsin is used to stain the AFB. It contains phenol red which helps the stain to penetrate through the cell wall, which is further assisted by heat addition. Carbolfuschin stains every cell.

What color would the positive cells stain?

Answer: The positive cells would stain red as phenol is red in color.

What dye is used as the counterstain in this reaction?

Answer: Carbol Fuschin stains every cell. Upon destaining with acid alcohol, the AFB cells do not get destained as AFBs are resistant decolorization by an acid. But the other cells (negative) get destained. Now, using methylene blue as a counter stain all the negative cells can be stained.

What color would the negative cells stain?

Answer: The negative cells will get stained with blue as they absorb methylene blue.