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 Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for gram-negative

Historical Examples of gram-negative

  • 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 organism is a short, thick diplobacillus, is frequently intracellular, and is Gram-negative (Fig. 126).

  • The bacillar threads are in places Gram-negative, in others Gram-positive, and bear small club-like swellings (see Fig. 14).

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

Medicine definitions for 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.

Science definitions for gram-negative


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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.