Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation, making positive identification possible. The thin peptidoglycan layer of their cell wall is sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. After staining with crystal violet, an alcohol wash is applied which decolorizes the bacteria showing that their peptidoglycan layer is too thin to retain the stain and enabling identification. A counterstain (safranin or fuchsine) is then added which recolorizes the bacteria red or pink.