Question

Gram $(+)$ and Gram $(-)$ forms of bacteria are differentiable through staining with

• A. Saffranin and Gentian Violet
• B. Saffranin and Iodine
• C. Acetocarmine and Iodine
• D. Crystal Violet and Iodine

Answer 1

The correct option is D Crystal Violet and Iodine

Gram staining procedure is based on the principle of the ability of microorganisms to retain the color of the stains used during the gram staining process. Gram-positive bacteria retain purple color after staining with Crystal Violet stain. Iodine is added as a mordant to form the crystal violet-iodine complex. They are not decolorized by treatment with alcohol. Whereas gram-negative bacteria are decolorized by the alcohol and lose the purple color of Crystal Violet stain. When again stained with second stain Saffranin, they retain pink color. This major difference is due to the difference in the cell wall component of both the bacteria. Gram-negative bacteria contain additional peptidoglycan layer and a thin layer of LPS layer.

Thus, the correct answer is 'Crystal Violet + Iodine.'