Gram Stain
•Differentiates bacteria into two groups: Gram positive and Gram negative
•Stain mechanism is generally related to the thickness of the cell wall, pore size and permeability properties of intact cell envelope
•Makes use of a primary stain (Crystal Violet), a mordant (Gram’s Iodine) a decolorizer (Alcohol or Acetone) and a counterstain (Safranin).
•Gram positive organisms stain blue while gram negative organisms stain red.
•Most cocci are gram positive; a third of all cocci, half of the bacilli, and all the spiral bacteria are gram negative.