Gram-positive and Gram-negative organisms form a complex of crystal violet and iodine within the bacterial cell during the Gram-staining procedure. Gm+ organisms are thought to resist decolorization by alcohol or acetone because cell wall permeability is markedly decreased when it is dehydrated by these solvents. Thus, the dye complex is entrapped within the cell, resist being washed out by the solvents, and Gm+ bacteria remain purple following this differential stain.
