In a standard Gram stain, what color do Gram-negative bacteria typically appear after the safranin counterstain is applied?

• A. Colorless (unstained)
• B. Green
• C. Pink to red
• D. Purple

Answer: (C)

Verified step by step guidance

1. Understand the purpose of the Gram stain: it differentiates bacteria into Gram-positive and Gram-negative based on their cell wall structure.
2. Recall that the primary stain, crystal violet, initially stains all bacteria purple.
3. During the decolorization step, Gram-negative bacteria lose the crystal violet stain because of their thinner peptidoglycan layer and higher lipid content, making them colorless at this point.
4. The safranin counterstain is then applied, which stains the now colorless Gram-negative bacteria pink to red, while Gram-positive bacteria remain purple because they retain the crystal violet.
5. Therefore, after the safranin counterstain, Gram-negative bacteria typically appear pink to red.