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Pronunciation: gram-pos'i-tiv

Definition: 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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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review date: Sep 19, 2016.