After Gram staining, what color do Gram-positive cells typically appear?

After Gram staining, what color do Gram-positive cells typically appear?

• A. Purple
• B. Pink
• C. Red
• D. Colorless

Answer: (A)

Gram staining differentiates bacteria by cell wall structure. Gram-positive cells have a thick peptidoglycan layer that traps and retains the crystal violet-iodine complex during the decolorization step, so they stay purple. In contrast, Gram-negative cells have a thinner peptidoglycan layer and an outer membrane that is disrupted by alcohol, causing the dye to wash out and the pink counterstain to show. So, after Gram staining, Gram-positive cells typically appear purple.

Gram staining differentiates bacteria by cell wall structure. Gram-positive cells have a thick peptidoglycan layer that traps and retains the crystal violet-iodine complex during the decolorization step, so they stay purple. In contrast, Gram-negative cells have a thinner peptidoglycan layer and an outer membrane that is disrupted by alcohol, causing the dye to wash out and the pink counterstain to show. So, after Gram staining, Gram-positive cells typically appear purple.