Which of the following basic dyes is commonly used as the counterstain in the Gram stain procedure?

• A. Crystal violet
• B. Malachite green
• C. Methylene blue
• D. Safranin

Answer: (D)

Verified step by step guidance

1. Understand the Gram stain procedure, which involves a primary stain, a mordant, a decolorizer, and a counterstain to differentiate bacterial cell wall types.
2. Identify the primary stain used in the Gram stain, which is Crystal violet, staining all cells initially.
3. Recognize that after decolorization, Gram-positive bacteria retain the Crystal violet, while Gram-negative bacteria lose it and need a counterstain to be visible.
4. Recall that the counterstain is a basic dye that stains the decolorized Gram-negative bacteria, providing contrast to the purple Gram-positive cells.
5. Know that Safranin is the commonly used counterstain in the Gram stain procedure, staining Gram-negative bacteria pink/red.