A gram stain is a test used to learn if bacteria are present in your body fluids or tissue.
The Gram stain is the most important staining procedure in microbiology. It is used to differentiate between gram positive organisms and gram negative organisms. Hence, it is a differential stain.
Gram staining involves a four-part process, which includes:
crystal violet, the primary stain
iodine, the mordant
a decolorizer made of acetone and alcohol
safranin, the counterstain