Which dye is primarily used in the Gram staining procedure?

The dye primarily used in the Gram staining procedure is crystal violet. This dye serves as the primary stain, which is crucial for differentiating between Gram-positive and Gram-negative bacteria. When the crystal violet is applied to a bacterial smear, it penetrates the cell wall of both types of bacteria. The procedure continues with a mordant (iodine) that helps to fix the dye inside the cells.

In Gram-positive bacteria, the thick peptidoglycan layer retains the crystal violet even after the decolorization step that follows. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and will lose the crystal violet during decolorization, eventually taking up the counterstain (safranin) that is applied afterward. This differential retention of the crystal violet dye is what ultimately allows for the classification of bacteria into two groups based on their cell wall structure and integrity.