Definition

Noun: A staining technique used in microbiology to classify bacteria into two broad categories based on the chemical and physical properties of their cell walls. The method involves staining bacterial samples with a crystal violet dye, followed by treatment with an iodine solution (Gram's solution), decolorization with an alcohol or acetone solvent, and counterstaining with a red dye such as safranin. Bacteria that retain the initial violet stain are classified as Gram-positive, appearing purple under a microscope. Bacteria that lose the violet stain and take up the red counterstain are classified as Gram-negative, appearing pink or red.

Usage

This term is used specifically in scientific contexts, particularly in microbiology, medicine, and laboratory diagnostics. - The primary use is to describe the laboratory procedure itself. - It is also used to refer to the classification principle (Gram-positive vs. Gram-negative) derived from this method.

Examples

• Describing the procedure:
  • The laboratory technician performed Gram's method on the clinical isolate to identify the bacteria.
  • Students learned Gram's method as a fundamental technique in their microbiology lab.
• Referring to the classification:
  • The results from Gram's method indicated the presence of Gram-negative rods.
  • Before the advent of modern genetic tests, Gram's method was a primary tool for bacterial identification.

Advanced Usage

• "Gram stain": This is a more common synonym for the procedure. While "Gram's method" refers to the technique, "Gram stain" can refer to both the technique and the resulting appearance of the bacteria.
  • The Gram stain showed mixed flora. (Here, it refers to the result/observation.)
• The method is foundational. Descriptions of bacterial characteristics often begin with their Gram reaction.
  • The pathogen was described as a facultatively anaerobic, Gram-negative coccobacillus.

Variants and Related Words

• Gram stain (n): The common name for the staining technique or its result.
• Gram-positive (adj): Describing bacteria that retain the crystal violet stain and appear purple.
• Gram-negative (adj): Describing bacteria that do not retain the crystal violet stain, take up the safranin counterstain, and appear pink/red.
• Gram's solution (n): The iodine-based mordant used in the staining process to fix the dye.
• Gram's procedure (n): A less common synonym for Gram's method.

Synonyms

• Gram staining
• Gram stain technique
• Gram's procedure

Notes on Meaning

The term has one primary, technical meaning related to bacterial classification. It is an eponym, named after the Danish bacteriologist Hans Christian Gram, who developed the technique in 1884. It does not have idiomatic or phrasal verb uses outside of this specific scientific context.

Noun

1. a staining technique used to classify bacteria; bacteria are stained with gentian violet and then treated with Gram's solution; after being decolorized with alcohol and treated with safranine and washed in water, those that retain the gentian violet are Gram-positive and those that do not retain it are Gram-negative