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; Gram's method

Example Sentences

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

A new medicine capable of combating Gram-negative bacteria, a particularly hardy type of bug with inner and outer membranes that antibiotics struggle to cross, hasn’t hit the market in 50 years.

From Los Angeles Times • Feb. 15, 2024

All strains show tendency to chain formation, some being arranged 116in chains of six to twenty-five segments, which may contain both Gram-positive and Gram-negative individuals.

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 Douglas, Loudon