What is the primary stain used in the Gram staining process?

The primary stain used in the Gram staining process is crystal violet. This stain is crucial because it has strong affinity for the peptidoglycan layer found in bacterial cell walls. In Gram-positive bacteria, the thick peptidoglycan layer retains crystal violet even after the decolorization step, resulting in a purple appearance. This characteristic is essential for distinguishing between Gram-positive and Gram-negative bacteria. In contrast, Gram-negative bacteria, which have a thinner peptidoglycan layer and an outer membrane, do not retain the crystal violet after the decolorization step, and they take up the counterstain (safranin), appearing pink instead. The use of crystal violet as the first step in the Gram staining process is foundational for identifying bacterial species and determining the cell wall structure, which informs treatment options and understanding of microbial behavior.