In the Gram stain procedure, what is the primary purpose of the decolorizer?

• A. To apply the counterstain to all bacterial cells
• B. To enhance the binding of iodine to the cell wall
• C. To remove the crystal violet stain from Gram-negative cells
• D. To fix the crystal violet stain within Gram-positive cells

Answer: (C)

Verified step by step guidance

1. Understand the role of each reagent in the Gram stain procedure: crystal violet (primary stain), iodine (mordant), decolorizer, and counterstain (usually safranin).
2. Recognize that the decolorizer is applied after the iodine step and before the counterstain step in the staining process.
3. Know that the decolorizer's function is to differentiate between Gram-positive and Gram-negative bacteria by selectively removing the crystal violet stain from certain cells.
4. Recall that Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet-iodine complex, while Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane that allows the decolorizer to wash out the crystal violet stain.
5. Conclude that the primary purpose of the decolorizer is to remove the crystal violet stain from Gram-negative cells, enabling them to take up the counterstain and appear pink/red, while Gram-positive cells remain purple.