Which dye stains gram-negative bacteria pink during the Gram stain procedure?

• A. Safranin
• B. Iodine
• C. Methylene blue
• D. Crystal violet

Answer: (A)

Verified step by step guidance

1. Understand the Gram stain procedure, which differentiates bacteria into Gram-positive and Gram-negative based on their cell wall properties.
2. Recall that the primary stain used is Crystal violet, which initially stains all bacteria purple.
3. Recognize that iodine acts as a mordant, forming a complex with Crystal violet to fix the dye inside the cells.
4. During the decolorization step, alcohol or acetone removes the dye from Gram-negative bacteria due to their thinner peptidoglycan layer, while Gram-positive bacteria retain the dye.
5. Identify that Safranin is the counterstain applied last, which stains the now colorless Gram-negative bacteria pink, allowing them to be visually distinguished from the purple Gram-positive bacteria.