What color do gram-positive bacteria stain?

Gram-positive bacteria stain purple due to the structure of their cell walls. When subjected to the Gram staining protocol, these bacteria retain the crystal violet dye during the washing steps. The thick peptidoglycan layer in their cell walls retains this dye even after the decolorization step, resulting in the characteristic purple coloration. This property helps differentiate them from gram-negative bacteria, which have a thinner peptidoglycan layer and do not retain the crystal violet after decolorization, instead taking up the counterstain (usually safranin), which gives them a red appearance. Understanding this is crucial for microbiological classification and identification, as well as for determining the appropriate treatment options for bacterial infections.