Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
Carbolfuchsin is a red dye used in microbiological staining techniques, particularly in the Ziehl-Neelsen acid-fast stain. It helps differentiate bacteria with waxy cell walls, such as Mycobacterium species.
Carbolfuchsin penetrates the waxy cell walls of acid-fast bacteria, allowing them to retain the red color even after decolorization.
It is commonly used in the Ziehl-Neelsen staining method for identifying Mycobacterium tuberculosis and other acid-fast organisms.
The primary stain in the Ziehl-Neelsen method is carbolfuchsin, which is followed by heating to facilitate dye penetration.
Decolorizing agents like acid-alcohol do not remove carbolfuchsin from acid-fast bacteria, making them stand out against a blue or green background when counterstained.
Carbolfuchsin can also be used in modified versions of staining techniques such as Kinyoun stain.
Related terms
Ziehl-Neelsen Stain: A differential staining technique used to identify acid-fast bacteria by retaining carbolfuchsin dye.
Acid-Fast Bacteria: Bacteria that resist decolorization by acids during staining and retain a red color due to their waxy cell walls.
Kinyoun Stain: A cold variation of the Ziehl-Neelsen stain that uses carbolfuchsin without heating.