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[gram-neg-uh-tiv] /ˈgræmˈnɛg ə tɪv/
adjective, (often lowercase)
(of bacteria) not retaining the violet dye when stained by Gram's method.
Origin of Gram-negative
First recorded in 1905-10; See origin at Gram's method Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for Gram-negative
Historical Examples
  • The Gram-positive bacteria are violet and the Gram-negative are red.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • This method is excellent for differentiating Gram-positive and Gram-negative organisms on the same slide.

    The Fundamentals of Bacteriology Charles Bradfield Morrey
  • The latter are Gram-negative, and vary greatly in both dimensions as well as in form.

    The Bacillus of Long Life Loudon Douglas
  • The organism is a short, thick diplobacillus, is frequently intracellular, and is Gram-negative (Fig. 126).

    A Manual of Clinical Diagnosis James Campbell Todd
  • The bacillar threads are in places Gram-negative, in others Gram-positive, and bear small club-like swellings (see Fig. 14).

    The Bacillus of Long Life Loudon Douglas
British Dictionary definitions for Gram-negative


designating bacteria that fail to retain the violet stain in Gram's method
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Gram-negative in Medicine

gram-negative or Gram-negative
Of, relating to, or being a bacterium that does not retain the violet stain used in Gram's method.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Gram-negative in Science
Relating to a group of bacteria that do not change color when subjected to the laboratory staining method known as Gram's method or Gram's stain. Gram-negative bacteria have relatively thin cell walls and are generally resistant to the effects of antibiotics or the actions of the body's immune cells. Gram-negative bacteria include E. coli and the bacteria that cause gonorrhea, typhoid fever, rickettsial fever, cholera, syphilis, plague, and Lyme disease. Compare gram-positive.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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