a staining technique used to classify bacteria, based on their ability to retain or lose a violet colour, produced by crystal violet and iodine, after treatment with a decolorizing agent
See also Gram-negative, Gram-positive
Word origin
C19: named after Hans Christian Joachim Gram (1853–1938), Danish physician
Gram's method in American English
(græmz)
a method of staining bacteria for the purpose of classification, involving treatment with crystal violet, an iodine solution, and alcohol: the violet stain is retained by Gram-positive bacteria or lost by Gram-negative bacteria when the alcohol is applied