Gram method
Gram stain an empirical staining procedure in which microorganisms are stained with crystal violet, treated with 1:15 dilution of strong iodine solution, decolorized with ethanol or ethanol-acetone, and counterstained with a contrasting dye, usually safranin O. Those microorganisms that retain the crystal violet stain are said to be gram-positive, and those that lose the crystal violet stain by decolorization but stain with the counterstain are said to be gram-negative. Gram-positive organisms that lose the stain easily, so that samples appear to be a mixture of gram-positive and gram-negative organisms, are said to be gram-variable.
Gram stain demonstrating gram-positive diplococci in sputum smear.
Medical dictionary.
2011.