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Grams stain

(Science: microbiology, technique) a method for differential staining of bacteria; smears are fixed by flaming, stained in a solution of crystal violet, treated with iodine solution, rinsed, decolorised, and then counterstained with safranin o.

gram-positive organisms stain purple black and gram-negative organisms stain pink; useful in bacterial taxonomy and identification, and also in indicating fundamental differences in cell wall structure.