Monday, July 30, 2007 ; 3:48 PM
For Bio Glossary:
Gram staining (or Gram's method) is an empirical method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls.
Gram-positive bacteria are those that retain a crystal violet dye during the Gram stain process.
Gram-negative bacteria are those that do not retain crystal violet dye in the Gram staining protocol. Gram-positive bacteria will retain the dark blue dye after an alcohol wash. In a Gram stain test, a counterstain (commonly Safranin) is added after the crystal violet, coloring all Gram-negative bacteria a red or pink color.