Procedure
- Fix to slide with heat or methanol
- Add crystal violet, and wait 60 seconds
- Wash with water then flood with iodine, and wait 60 seconds
- Wash with water then decolorize with 95% ethanol or acetone
- Counter-stain with safrinin, wait 30 seconds then wash off with water
Interpretation
- Gram-positive = blue
- Gram-negative = red
- Peptidoglycan layer (cell wall) is thick with extensive cross-linking in gram-positive
