What is the purpose of a decolorizer in the Gram stain? In the acidfast stain?
The correct answer and explanation is:
In the Gram stain, the decolorizer serves to differentiate bacterial cells based on the structure of their cell walls. The decolorizer, usually alcohol or acetone, works by disrupting the lipid layer in the outer membrane of Gram-negative bacteria. As a result, the crystal violet stain is washed out from these cells. In contrast, Gram-positive bacteria have a thicker peptidoglycan layer, which retains the crystal violet stain even after the decolorization step. This differential staining process is crucial for identifying bacteria based on their cell wall composition. After decolorization, Gram-negative bacteria take up a counterstain, typically safranin, which stains them pink, while Gram-positive bacteria retain the purple color of the crystal violet.
In the acid-fast stain, the purpose of the decolorizer is to differentiate acid-fast bacteria, like Mycobacterium, from non-acid-fast bacteria. The decolorizer in this method is an acid-alcohol solution, which removes the primary stain, carbolfuchsin, from non-acid-fast cells. Acid-fast bacteria, however, have a waxy cell wall containing mycolic acid, which binds tightly to the carbolfuchsin stain and prevents it from being washed out. As a result, acid-fast bacteria retain the red color of the carbolfuchsin even after the decolorization step. Non-acid-fast bacteria, which lack the mycolic acid, will lose the carbolfuchsin and take up the counterstain, usually methylene blue, appearing blue under a microscope.
Thus, the role of the decolorizer in both stains is to distinguish between different types of bacteria based on the structural differences in their cell walls, which ultimately helps in bacterial identification and classification.