Acid Fast

Acid fast organisms have a thick cell wall that is waxy due to the presence of mycolic acids. As a result, these organisms resist decolourization by acid alcohol.

	Ziehl-Neelsen (ZN) Stain	Kinyoun Stain
Primary Stain	Carbol fuchsin Heated on slide	Carbol fuchsin Uses higher phenol concentration at normal temperature
Decolourizer	3% acid alcohol*	3% acid alcohol*
Counterstain	Methylene blue	Methylene blue
	ZN (Zinc) hot	Kinyoun, cold, concentrated

*Modified acid fast stains use a lower concentration of acid alcohol (0.5-1.0%) for organisms with less mycolic acid present in their cell walls.

Acid Fast Organisms

• Mycobacteria (e.g., M. tuberculosis, M. leprae, etc.)

Partially Acid Fast Organisms

• Nocardia
• Legionella