Gram′s crystal violet solution

Gram’s crystal violet solution, also known as gentian violet or hexamethyl pararosaniline, is a basic, cationic, acidotropic aminoarylmethane dye. It is a hexa-N-methylated triaminotriphenylmethane with a moderately sized lipophilic cation and a slightly nonplanar conjugated system. It is used in bacteriology as the primary stain in Gram staining to differentiate Gram-positive and Gram-negative bacteria. It is known to possess antibacterial and antifungal properties.

Crystal violet is the primary stain in Gram staining. It infiltrates the peptidoglycan-rich cell wall of Gram-positive bacteria, and forms complexes with Gram’s iodine that are entrapped and retain the purple color even after decolorization. Thus, Gram-positive bacteria can be differentiated from Gram-negative bacteria whose peptidoglycan layer is considerably thinner and does not retain crystal violet.

The antimicrobial effects of crystal violet are caused by free radical generation and the formation of unionized dye-bacteria complexes. It also inhibits bacterial protein synthesis and cell wall formation and is especially effective against Gram-positive bacteria.