What structural feature allows Gram-positive cells to retain the crystal violet-iodine complex?

What structural feature allows Gram-positive cells to retain the crystal violet-iodine complex?

• A. Thick peptidoglycan layer
• B. Outer membrane
• C. Thin peptidoglycan layer
• D. Capsule

Answer: (A)

The key factor is the thick peptidoglycan layer in Gram-positive cell walls, which traps the crystal violet–iodine complex during the stain processing. This dense, extensive peptidoglycan matrix holds onto the dye and becomes dehydrated and tightened by the alcohol step, preventing the complex from washing out. In contrast, cells with thinner peptidoglycan and an outer membrane (Gram-negative) lose the dye during decolorization, allowing a counterstain to be taken up. A capsule doesn’t influence this retention. So, the thick peptidoglycan layer is what enables Gram-positive cells to retain the crystal violet–iodine complex.

The key factor is the thick peptidoglycan layer in Gram-positive cell walls, which traps the crystal violet–iodine complex during the stain processing. This dense, extensive peptidoglycan matrix holds onto the dye and becomes dehydrated and tightened by the alcohol step, preventing the complex from washing out. In contrast, cells with thinner peptidoglycan and an outer membrane (Gram-negative) lose the dye during decolorization, allowing a counterstain to be taken up. A capsule doesn’t influence this retention. So, the thick peptidoglycan layer is what enables Gram-positive cells to retain the crystal violet–iodine complex.