Definition

1. Adjective:
   • Relating to a classification of bacteria: Describes bacteria that do not retain the crystal violet stain used in the Gram staining method, a common laboratory test. These bacteria appear pink or red under a microscope after the staining procedure.

Usage

• The term is primarily used in scientific, medical, and microbiological contexts to classify and describe bacterial species based on their cell wall structure.
• It is typically hyphenated when used as a compound adjective before a noun (e.g., gram-negative bacteria). It can also be used after a linking verb (e.g., The organism is gram-negative).

Examples

• Adjective:
  • E. coli is a gram-negative bacterium commonly found in the intestines.
  • The laboratory report confirmed the infection was caused by a gram-negative rod.
  • This antibiotic is particularly effective against gram-negative organisms.

Advanced Usage

• "Gram-negative" is part of a fundamental binary classification system in bacteriology, contrasting with "gram-positive." The difference is crucial for diagnosis and treatment, as the cell wall structure affects antibiotic susceptibility.
• The term is named after Hans Christian Gram, the Danish bacteriologist who developed the staining technique. It is often capitalized as Gram-negative, though the lowercase form is also widely accepted.

Variants and Related Words

• Gram-positive (adj): Describing bacteria that retain the crystal violet stain and appear purple under a microscope.
  • Staphylococcus aureus is a gram-positive coccus.
• Gram stain (n): The differential staining technique used to classify bacteria as gram-positive or gram-negative.
  • The doctor ordered a Gram stain of the sputum sample.

Synonyms

• There are no direct synonyms for this specific technical classification. Descriptive phrases could include "bacteria that do not retain crystal violet stain" or "pink-staining bacteria," but these are explanations, not synonyms.

Related Phrases

• Gram-negative sepsis: A serious, systemic infection caused by gram-negative bacteria.
  • The patient was admitted to the ICU with suspected gram-negative sepsis.
• Gram-negative bacilli: A common morphological description for rod-shaped gram-negative bacteria.
  • The culture grew a gram-negative bacilli.

Related Idioms

• There are no common idioms using the term gram-negative.

Adjective

1. (of bacteria) being of or relating to a bacterium that does not retain the violet stain used in Gram's method