gram stain


gram stain
Staining technique for the initial identification of bacteria, devised in 1884 by the Danish physician Hans Christian Gram (1853–1938).

The stain reveals basic differences in the biochemical and structural properties of a living cell. A slide containing a smear of bacteria is treated with a purple dye; the slide is then dipped in an iodine solution, followed by an organic solvent (such as alcohol) that can dissolve the dye. Gram-positive bacteria remain purple because they have a thick cell wall that the solvent cannot easily penetrate; gram-negative bacteria lose their colour because they have thin cell walls that allow the solvent to penetrate and remove the dye.

* * *

      a widely used microbiological staining technique that greatly aids in the identification and characterization of bacteria. It was devised by a Danish physician, Hans Christian Gram, in 1884. The Gram reaction reflects fundamental differences in the biochemical and structural properties of bacteria. A slide containing a heat-fixed smear of bacterial cells is treated with crystal-violet stain (a basic dye), during which the cells turn purple. The slide is then flushed with an iodine solution, followed by an organic solvent (such as alcohol or acetone). Gram-positive bacteria remain purple because they have a single thick cell wall that is not easily penetrated by the solvent; gram-negative bacteria, however, are decolorized because they have cell walls with much thinner layers that allow removal of the dye by the solvent. In a final step, a counterstain, such as safranin, is added and stains the gram-negative cells red.

* * *


Universalium. 2010.

Look at other dictionaries:

  • Gram stain — Gram stain. См. окрашивание по Граму. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Gram stain — noun a staining technique used to classify bacteria; bacteria are stained with gentian violet and then treated with Gram s solution; after being decolorized with alcohol and treated with safranine and washed in water, those that retain the… …   Useful english dictionary

  • Gram stain — The Danish bacteriologist J.M.C. Gram (1853 1938) devised a method of staining bacteria using a dye called crystal (gentian) violet. Gram s method helps distinguish between different types of bacteria. The gram staining characteristics of… …   Medical dictionary

  • Gram stain — A heat fixed bacterial smear is stained with crystal violet (methyl violet), treated with 3% iodine/potassium iodide solution, washed with alcohol and counterstained. The method differentiates bacteria into two main classes, Gram positive and… …   Dictionary of molecular biology

  • Gram stain — noun see Gram s stain …   New Collegiate Dictionary

  • Gram stain — noun Medicine a staining technique for the preliminary distinction of bacteria between two categories (Gram positive and Gram negative). Origin C19: named after the Danish physician Hans C. J. Gram …   English new terms dictionary

  • Gram stain — A differential staining procedure that divides bacteria into gram positive and gram negative groups based on their ability to retain crystal violet when decolorized with an organic solvent such as ethanol …   Dictionary of microbiology

  • gram stain test — A laboratory test for symptoms of gonorrhea, universally used, and considered to be practically conclusive, certainly so when the objective symptoms are present. Peterson v Widule, 157 Wis 641, 147 NW 966. granage (gran aj). Same as grainage …   Ballentine's law dictionary

  • Gram staining — (or Gram s method) is an empirical method of differentiating bacterial species into two large groups (Gram positive and Gram negative) based on the chemical and physical properties of their cell walls.cite book | last = Bergey | first = David H.… …   Wikipedia

  • Gram-positive — bacteria retain the color of the crystal violet stain in the Gram stain. This is characteristic of bacteria that have a cell wall composed of a thick layer of a particular substance (called peptidologlycan). The Gram positive bacteria include… …   Medical dictionary


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.