Refers to the ability of a type of bacterium to resist decolorization with alcohol after being treated with crystal violet stain, which imparts a violet color to the bacteria when viewed by light microscopy. This reaction is usually an indication that the outer structure of the bacterium consists of a cytoplasmic membrane surrounded by a thick rigid bacterial cell wall composed of peptidoglycan.
See: Gram stain
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Examples: glitazone, GI cocktail, etc.