Stain, Gram
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 bacteria are denoted as positive or negative, depending upon whether the bacteria take up and retain the crystal violet stain or not. 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 (specifically, peptidologlycan containing teichoic and lipoteichoic acid complexed to the peptidoglycan). The Gram-positive bacteria include staphylococci ("staph"), streptococci ("strep"), pneumococci, and the bacterium responsible for diphtheria (Cornynebacterium diphtheriae) and anthrax (Bacillus anthracis). Gram-negative bacteria lose the crystal violet stain (and take the color of the red counterstain) in Gram's method of staining. This is characteristic of bacteria that have a cell wall composed of a thin layer of a particular substance (specifically, peptidoglycan covered by an outer membrane of lipoprotein and lipopolysaccharide containing endotoxin). The Gram-negative bacteria include most of the bacteria normally found in the gastrointestinal tract that can be responsible for disease as well as gonococci (venereal disease) and meningococci (bacterial meningitis). The organisms responsible for cholera and bubonic plague are Gram-negative.

Medical dictionary. 2011.

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  • 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

  • Gram-positive bacteria — Gram positive bacteria, stained purple, of both the bacillus (“rod shaped”) and coccus (spherical) forms.  A few Gram negative bacteria are also present, stained pink.  Numbered ticks are eleven (11) microns apart. Gram positive… …   Wikipedia

  • Gram-negative — bacteria lose the crystal violet stain (and take the color of the red counterstain) in Gram s method of staining. This is characteristic of bacteria that have a cell wall composed of a thin layer of a particular substance (called peptidoglycan).… …   Medical dictionary

  • Gram's stain — or Gram stain gram n 1) a method for the differential staining of bacteria that involves fixing the bacterial cells to a slide and staining usu. with the basic dye crystal violet, treating with an iodine solution to fix the dye, washing with… …   Medical dictionary

  • gram-variable — gram vari·able gram ver ē ə bəl, var adj staining irregularly or inconsistently by Gram s stain * * * gram var·i·a·ble (gram varґe ə bəl) appearing to be a mixture of gram positive and gram negative organisms, said of gram positive… …   Medical dictionary

  • Gram's solution — gramz n a watery solution of iodine and the iodide of potassium used in staining bacteria by Gram s stain Gram gräm Hans Christian Joachim (1853 1938) Danish physician. Gram introduced his method for the differential staining of bacteria in 1884 …   Medical dictionary

  • Gram'smethod — Gram s method (grămz) n. A staining technique used to classify bacteria in which a bacterial specimen is first stained with crystal violet, then treated with an iodine solution, decolorized with alcohol, and counterstained with safranine. Gram… …   Universalium

  • Gram's 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 — 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

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