- venereal disease) and meningococci (bacterial meningitis). The organisms responsible for cholera and bubonic plague are Gram-negative. The Danish bacteriologist J.M.C. Gram (1853-1938) devised this 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.
* * *Refers to the inability of a bacterium to resist decolorization with alcohol after being treated with Gram crystal violet. However, following decolorization, these bacteria can be readily counterstained with safranin, imparting a pink or red color to the bacterium when viewed by light microscopy. This reaction is usually an indication that the outer structure of the bacterium consists of a cytoplasmic (inner) membrane surrounded by a relatively thin peptidoglycan layer, which in turn, is surrounded by an outer membrane. See Gram stain.
* * *gram-neg·a·tive 'gram-'neg-ət-iv adj not holding the purple dye when stained by Gram's stain used chiefly of bacteria
* * *gram-neg·a·tive (gram-negґə-tiv) losing the stain or decolorized by alcohol in the Gram method of staining, a primary characteristic of bacteria having a cell wall composed of a thin layer of peptidoglycan covered by an outer membrane of lipoprotein and lipopolysaccharide. Cf. gram-positive.
Medical dictionary. 2011.
Look at other dictionaries:
Gram-negative — [gram′neg′ə tiv] adj. [also g ] designating bacteria that do not retain the color stain: see GRAM S METHOD … English World dictionary
Gram-negative — Bacillus cereus, lichtmikroskopisch, Gram Färbung: grampositiv Pseudomonas aeruginosa, lichtmikroskopisch, Gram Fä … Deutsch Wikipedia
Gram-négative — Gram négatif Les bactéries à Gram négatif sont mises en évidence par une technique de coloration appelée coloration de Gram. Les bactéries à Gram négatif apparaissent alors roses au microscope. La technique de coloration repose sur les… … Wikipédia en Français
Gram-negative — /gram neg euh tiv/, adj. (often l.c.) (of bacteria) not retaining the violet dye when stained by Gram s method. [1905 10; see GRAM S METHOD] * * * … Universalium
Gram-negative — Gram′ neg′ative [[t]græm[/t]] adj. (often l.c.) mcr lab (of bacteria) not retaining the violet dye when stained by Gram s method • Etymology: 1905–10 … From formal English to slang
Gram-negative — adjective (of bacteria) being of or relating to a bacterium that does not retain the violet stain used in Gram s method • Similar to: ↑negative, ↑disconfirming • Topics: ↑bacteria, ↑bacterium … Useful english dictionary
gram-negative — adjective Date: 1907 not holding the purple dye when stained by Gram s stain used chiefly of bacteria … New Collegiate Dictionary
gram-negative — adjective (of a bacterium) that is not stained violet by Grams method Ant: gram positive … Wiktionary
gram-negative — (about bacteria) not retaining the primary violet stain after being stained by Gram s method … English contemporary dictionary
Gram-negative — adjective see Gram stain … English new terms dictionary