Gram stain

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Definition

Noun: 1. A differential staining technique used in microbiology to classify bacteria into two major groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls. The technique involves staining bacterial cells with a crystal violet dye, fixing it with an iodine solution, decolorizing with alcohol or acetone, and counterstaining with a red dye such as safranin.

Usage

The term "gram stain" is used primarily as a noun to refer to the laboratory procedure itself or to the result of that procedure. * The laboratory report included the gram stain results for the spinal fluid. * Performing a gram stain is the first step in identifying an unknown bacterium. * The gram stain showed Gram-positive cocci in clusters.

Advanced Usage
  • "To Gram-stain" (verb, often hyphenated): The procedure can be verbalized, meaning to perform the Gram stain technique on a sample.
    • The technician will Gram-stain the culture to determine the next steps.
  • As an adjective (Gram-stained): Describing a sample that has undergone the procedure.
    • Examine the Gram-stained smear under the microscope.
Variants and Related Words
  • Gram-positive (adj.): Referring to bacteria that retain the crystal violet stain and appear purple after the Gram stain procedure, due to a thick peptidoglycan layer in their cell wall.
  • Gram-negative (adj.): Referring to bacteria that lose the crystal violet stain and take up the red counterstain, appearing pink or red, due to a thinner peptidoglycan layer and an outer membrane.
  • Gram's method / Gram's procedure: Alternative names for the technique, named after its inventor, Hans Christian Gram.
Synonyms
  • Differential stain
  • Bacterial stain
  • Gram's method
Related Phrases
  • Gram stain morphology: A description of the bacterial shape (e.g., cocci, rods) and staining result (positive or negative) as observed under the microscope.
    • The gram stain morphology was reported as Gram-negative rods.
  • Gram stain reaction: The outcome of the test (i.e., whether the bacteria are Gram-positive or Gram-negative).
    • The Gram stain reaction is a critical piece of diagnostic information.
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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