What color do Gram-positive bacteria appear under the microscope after Gram staining?

What color do Gram-positive bacteria appear under the microscope after Gram staining?

• A. Pink
• B. Dark Purple
• C. Green
• D. Yellow

Answer: (B)

Dark purple is the color Gram-positive bacteria appear after Gram staining. This happens because their cell walls have a thick layer of peptidoglycan that traps the crystal violet–iodine complex during the staining and decolorization steps, so the dye stays inside the cells and they look dark purple under the microscope. In contrast, bacteria with thinner peptidoglycan and an outer membrane (Gram-negative) lose the violet dye during decolorization and take up a red counterstain, appearing pink.

Dark purple is the color Gram-positive bacteria appear after Gram staining. This happens because their cell walls have a thick layer of peptidoglycan that traps the crystal violet–iodine complex during the staining and decolorization steps, so the dye stays inside the cells and they look dark purple under the microscope. In contrast, bacteria with thinner peptidoglycan and an outer membrane (Gram-negative) lose the violet dye during decolorization and take up a red counterstain, appearing pink.