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Etymology: Hans C.J. Gram
the method of staining microorganisms using a violet stain, followed by an iodine solution; decolorizing with an alcohol or acetone solution; and counterstaining with safranin. The retention of either the violet color of the stain or the pink color of the counterstain serves as a primary means of identifying and classifying bacteria. Also called Gram's method. See also gram-negative, gram-positive.
Gram's staina stain taken up by the Gram-positive bacteria that differentiates these from bacteria which fail to take up the stain (Gram-negative types). The initial stain is crystal violet/iodine complex, and Gram-negative bacteria are decolorized with alcohol whilst Gram-positive bacteria retain a blue/purple colour.
A stain used in microbiology to classify bacteria and help identify the species to which they belong. This identification aids in determining treatment.
a staining procedure in which bacteria are stained with crystal violet, treated with strong iodine solution, decolorized with ethanol or ethanol-acetone and counterstained with a contrasting dye, usually safranin. The iodine alters the structure of the cell wall in gram-positive bacteria so that the crystal violet is locked within the cell. Organisms that retain the crystal violet stain are deep purple in color and are classed as gram-positive and those losing the crystal violet stain are classified as gram-negative and are red in color.