Which staining method is used to distinguish between different types of bacterial cell walls?

The Gram stain is a differential staining technique that specifically distinguishes between two major types of bacterial cell walls: Gram-positive and Gram-negative. This method relies on the structural differences in the cell walls, primarily the amount of peptidoglycan present.

In a Gram stain, the first step involves applying a crystal violet dye, which stains all the cells. This is followed by a mordant, usually iodine, which helps to fix the dye inside the cell. After that, a decolorization step with alcohol or acetone occurs, which has a significant effect on the two types of cells. In Gram-positive bacteria, the thick layer of peptidoglycan retains the crystal violet dye even after the decolorization step, causing them to appear purple. Conversely, Gram-negative bacteria, which have a thinner peptidoglycan layer surrounded by an outer membrane, lose the crystal violet during decolorization and take up a counterstain (commonly safranin), appearing pink.

This clear differentiation based on cell wall structure is critical for identification and classification of bacteria, as well as for guiding antibiotic treatment, since Gram-positive and Gram-negative bacteria often respond differently to various antibiotics. Other staining methods, such as simple stains, negative stains, or