What feature explains why Gram-positive bacteria retain the crystal violet-iodine complex during Gram staining?

• A. Thick peptidoglycan with teichoic acids
• B. Outer membrane
• C. Periplasmic space
• D. Capsule

Answer: (A)

Retention of the crystal violet-iodine complex in Gram staining comes from the cell wall structure of Gram-positive bacteria. Their thick, dense peptidoglycan layer forms a sturdy, mesh-like network that traps the CV-I complex during the decolorization step. The teichoic acids interwoven in this wall add negative charges and help bind the dye, making it difficult for the complex to wash out. In contrast, Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane that is disrupted by alcohol, allowing the CV-I complex to be washed away. capsules and the periplasmic space don’t contribute to retaining CV-I in the same way. Therefore, the feature responsible is the thick peptidoglycan layer with teichoic acids.