Gram method

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Definition

Noun: A fundamental laboratory staining technique in microbiology used to classify bacteria into two broad categories (Gram-positive and Gram-negative) based on the structural differences in their cell walls. The method involves staining bacterial samples with a crystal violet dye, fixing it with an iodine solution, decolorizing with alcohol or acetone, and then applying a counterstain such as safranin.

Usage

The Gram method is a primary diagnostic tool. - It is used to initiate the identification process of an unknown bacterial specimen. - The results guide the selection of appropriate antibiotics, as Gram-positive and Gram-negative bacteria often respond differently to treatments. - The technique is performed by first heat-fixing bacteria to a glass slide.

Examples
Advanced Usage
  • "Gram stain" as a synonym: While "Gram method" refers to the overall technique, "Gram stain" is often used interchangeably to describe both the procedure and the resulting visual appearance of the bacteria.
  • Interpretation: A Gram-positive result (purple/blue cells) indicates a thick peptidoglycan layer in the cell wall. A Gram-negative result (pink/red cells) indicates a thinner peptidoglycan layer and an outer membrane.
Variants and Related Words
  • Gram stain (n): The common synonym for the Gram method; also refers to the specific staining reagents used.
  • Gram-positive (adj): Describing bacteria that retain the crystal violet stain and appear purple.
  • Gram-negative (adj): Describing bacteria that lose the crystal violet stain, take up the counterstain, and appear pink or red.
  • Gram's solution (n): The iodine-based mordant used in the staining process to fix the dye.
Synonyms
  • Gram staining technique
  • Gram's procedure
  • Bacterial differential staining
Related Phrases
  • "To be Gram-variable": Refers to some bacteria or cultures that may stain irregularly, showing both positive and negative reactions.
  • "Perform a Gram stain": The standard phrasing for carrying out the method in a laboratory 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

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