AAT Bioquest

What is the primary stain for gram staining?

Posted August 23, 2022


Crystal violet is the primary stain for gram staining. It is an organic chloride salt that belongs to the triphenylmethane type alkaline dyes. Crystal violet may also be called Methyl Violet 10B, Gentian Violet, Basic Violet 3 or Hexamethyipararosaline chloride. When used in gram staining, crystal violet amplifies the contrast between gram-positive bacteria and gram-negative bacteria. 

Two stains are used in the gram staining procedure – crystal violet, which is the primary stain, and safranin. Staining with crystal violet is the first step in the gram staining procedure. When applied to the sample, the cell walls of some bacteria are able to absorb the stain due to the presence of peptidoglycan. Gram positive bacteria, which have a denser peptidoglycan layer, retain the crystal violet stain and appear purple or purple-brown under a microscope. Gram negative bacteria are unable to retain the primary stain and are instead stained by safranin in the final staining stage. Gram negative bacteria appear pink under the microscope.  

Additional resources

Gram Staining

MycoLight™ Rapid Fluorescence Bacterial Gram Stain Kit

MycoLight™ Rapid Fluorescence Gram-Positive Bacteria Staining Kit