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LEVEL I
Materials
Procedure
Rub lightly!
Gram-positive bacteria retain crystal violet after washing with 95% ethanol, while gram-negative bacteria lose the purple dye after washing with 95% ethanol. The positive or negative reaction is a measure of the presence or absence of specific polysaccharide components of their cell walls. Safranin is used as a pink counterstain, so that Gram - cells can be visualized. In practice then, the distinction is made between purple cells (+) and pink cells(-).