In the Gram stain procedure, which reagent serves as the decolorizer?

• A. Crystal violet
• B. Ethanol or an acetone-alcohol mixture
• C. Gram’s iodine
• D. Safranin

Answer: (B)

Verified step by step guidance

1. Understand the purpose of each reagent in the Gram stain procedure: Crystal violet is the primary stain that colors all cells purple initially.
2. Recognize that Gram's iodine acts as a mordant, forming a complex with crystal violet to fix the dye inside the cell walls.
3. Identify the decolorizer step, which selectively removes the primary stain from certain cells based on their cell wall properties.
4. Know that the decolorizer is typically ethanol or an acetone-alcohol mixture, which dissolves the outer membrane of Gram-negative bacteria and removes the crystal violet-iodine complex from them.
5. Finally, safranin is used as a counterstain to color the decolorized Gram-negative cells pink/red, allowing differentiation from Gram-positive cells that remain purple.