Pertaining to one of the most important ways of classifying bacteria by means of the differences in the way they stain. The set of bacteria that are not able to be stained (blue) when treated with the gram staining procedure. Gram negativity (and gram positivity) is conferred not by the chemical constituents of the bacteria, but rather by the physical structure of the bacteria cell wall. The staining procedure involves the staining of all cells in a sample with a blue dye. Gram-negative bacteria have a very thin peptidoglycan cell wall (capsule). Hence, the washing procedure, which is an integral part of the overall staining procedure, washes out the blue dye (known as crystal violet). This leaves the gram-negative bacteria colorless. The cells are then stained with a red acidic counterstain (dye) such as acid fuchsin or safranine. After treatment with counterstain the gram-negative cells are red and the grampositive cells are blue.
Losing the crystal violet stain and taking the color of the red counterstain in Gram’s method of staining, a primary characteristic of certain microorganisms.
When subjected to Gram’s stain, certain bacteria exhibit a distinctive pink hue.