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• Gram-negative
  Gram-negative

  adjective

  (of bacteria) not retaining the violet dye when stained by Gram's method.
• gram-negative
  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.

Gram-negative

American  

[gram-neg-uh-tiv] / ˈgræmˈnɛg ə tɪv /

adjective

(often lowercase)

1. (of bacteria) not retaining the violet dye when stained by Gram's method.

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Gram-negative British  

adjective

1. designating bacteria that fail to retain the violet stain in Gram's method

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gram-negative Scientific  

1. 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.

2. Compare gram-positive

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Etymology

Origin of Gram-negative

First recorded in 1905–10; see origin at Gram's method

Example Sentences

See Examples For:

Gram-negative gram-negative

This data will then be fed into the AI so it can learn what it takes for an antibiotic to persist inside a Gram-negative bacterium.

From BBC ● Nov. 18, 2025

Gram-negative species can block antibiotics from getting in and rapidly pump out those that penetrate the bacterial defences – making them tough to treat.

From BBC ● Nov. 18, 2025

Fusobacterium is a Gram-negative microbe found in the GI tract and the oral cavity, and previous studies have connected it to the development of CRC.

From Science Daily ● Apr. 4, 2024

Carbapenem-resistant A. baumannii is a type of Gram-negative bacteria, a vexing category of superbugs.

From Los Angeles Times ● Jan. 3, 2024

The latter are Gram-negative, and vary greatly in both dimensions as well as in form.

From The Bacillus of Long Life a manual of the preparation and souring of milk for dietary purposes, together with and historical account of the use of fermente by Loudon Douglas

Gram-positive and gram-negative bacteria differ in the composition of their cell walls.

From Science Daily ● May 29, 2024

The experimental dressing had excellent antibacterial performance against gram-negative and gram-positive bacterial species, and effectively eradicated E. coli and staph bacteria in testing.

From Science Daily ● Feb. 8, 2024

Methicillin-resistant Staphylococcus aureus and drug-resistant tuberculosis raised alarms; additionally, so-called gram-negative bacteria were proving evermore resistant to antibiotics.

From Washington Post ● Jan. 18, 2023

In gram-negative bacteria, the proton gradient that supplies the free energy to convert ADP into ATP is established across the inner membrane.

From Textbooks ● Jun. 9, 2022

Cells believe that it signifies the presence of gram-negative bacteria, and they will stop at nothing to avoid this threat.

From "The Lives of a Cell" by Lewis Thomas