Definition

Noun: A specific chemical preparation used as a critical component in Gram's method for bacterial classification. It is an iodine-based reagent that fixes the primary stain (crystal violet) within the cell walls of certain bacteria.

Usage

Gram's solution is used exclusively in microbiology laboratories during the Gram staining procedure. It is applied after the initial crystal violet stain and before the decolorization step. Its function is to form a crystal violet-iodine complex within the bacterial cell.

Examples

• Noun:
  • The technician carefully flooded the slide with Gram's solution for one minute.
  • Preparing Gram's solution requires precise measurements of iodine and potassium iodide.
  • The effectiveness of the stain depends on the quality of the Gram's solution.

Advanced Usage

• "To act as a mordant": In the staining context, Gram's solution acts as a mordant, a substance that fixes a dye. It is not a stain itself but a necessary chemical to make the primary stain adhere properly to gram-positive bacteria.
  • In the procedure, Gram's solution acts as a mordant, trapping the crystal violet in the thick peptidoglycan layer.

Variants and Related Words

• Gram stain (n): The complete differential staining technique used to classify bacteria as gram-positive or gram-negative.
  • The Gram stain is a fundamental diagnostic tool in clinical microbiology.
• Gram-positive (adj): Describing bacteria that retain the crystal violet stain after treatment with Gram's solution and decolorizer, appearing purple under a microscope.
  • Staphylococcus aureus is a common gram-positive bacterium.
• Gram-negative (adj): Describing bacteria that lose the crystal violet stain after decolorization and take up the counterstain (safranin), appearing pink or red.
  • E. coli is an example of a gram-negative bacterium.

Synonyms

• Iodine mordant: A technical term describing its function.
• Gram's iodine: A common alternative name for the solution.

Notes on Different Meanings

This term has a single, highly specialized meaning in the field of microbiology and histology. It is not used in general contexts.

Noun

1. a solution used in staining bacteria by Gram's method; consists of one part iodine and two parts potassium iodide and 300 parts water