In this expression gram begins with lowercase g but: Gram stain. 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.Gram stain
