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Gram negative Used of a micro-organism that when stained by Gram's method does not retain the purplish dye, methyl violet, but only the red counter-stain carbol fuchsin. Stained Gram negative organisms appear red. The whole class of medically important bacteria can be divided into a large GRAM POSITIVE group and a smaller Gram negative group. This division is an important step in identification. (Hans Christian Joachim Gram, 1853–1938, Danish physician).