Definitions for gram-negativegræm
This page provides all possible meanings and translations of the word gram-negative
(of bacteria) being of or relating to a bacterium that does not retain the violet stain used in Gram's method
that is not stained violet by Gram's method
Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation, making positive identification possible. The thin peptidoglycan layer of their cell wall is sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. After staining with crystal violet, an alcohol wash is applied which decolorizes the bacteria showing that their peptidoglycan layer is too thin to retain the stain and enabling identification. A counterstain is then added which recolorizes the bacteria red or pink. Gram-positive bacteria have a thicker peptidoglycan layer in their cell wall outside the cell membrane, which retains the crystal violet stain during the alcohol wash, so long as it is timed correctly. The counter stain may also be absorbed by gram-positive bacteria but the darker crystal violet stain predominates.
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"gram-negative." Definitions.net. STANDS4 LLC, 2016. Web. 12 Feb. 2016. <http://www.definitions.net/definition/gram-negative>.