In the Gram stain procedure, which dye is used as the counterstain?

• A. Iodine (Gram's iodine)
• B. Crystal violet
• C. Acetone-alcohol decolorizer
• D. Safranin

Answer: (D)

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. Know that acetone-alcohol is the decolorizer, which removes the primary stain from Gram-negative cells but not from Gram-positive cells.
4. Identify that the counterstain is applied after decolorization to stain the cells that lost the primary stain, providing contrast.
5. Recall that Safranin is the counterstain used in the Gram stain procedure to color Gram-negative bacteria pink or red.