Term: Gram stain
https://doi.org/10.1351/goldbook.G02681

Definition:
A set of two stains that are used to stain (crystal violet and iodine) and counterstain (fuchsin) bacteria. gram-negative bacteria are completely decolorized after treating the stained bacteria with ethanol or acetone and can be visualized by the counterstain. They have a complex cell wall in which the peptidoglycan layer is covered by lipopolysaccharides in an outer membrane structure. gram-positive bacteria resist decolorization by ethanol or acetone, they retain the initial gram stain. They have a cell wall consisting predominantly of peptidoglycan not overlayed by an outer membrane.

Related Terms:
1) gram (http://doi.org/10.1351/goldbook.G02680).
2) peptidoglycan (http://doi.org/10.1351/goldbook.P04480).
3) lipopolysaccharides (http://doi.org/10.1351/goldbook.L03574).
4) membrane (http://doi.org/10.1351/goldbook.MT06878).

Source: PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 155 (https://doi.org/10.1351/pac199264010143)

Citation: 'Gram stain' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.G02681

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