Carbol fuchsin

Carbol fuchsin is a mix of phenol and basic fuchsin, used in bacterial staining procedures. It is commonly used in the staining of mycobacteria as it has an affinity for the mycolic acids found in their cell walls.

Composition

Carbol fuchsin is composed of basic fuchsin, phenol, and ethanol. Basic fuchsin is the primary stain, while phenol makes the cell wall of the bacteria permeable to the stain. Ethanol acts as a solvent.

Uses

Carbol fuchsin is used in the Ziehl-Neelsen stain, a type of Acid-fast stain, to identify acid-fast organisms, primarily Mycobacteria. It is also used in the Schaeffer-Fulton stain to stain endospores.

Preparation

Carbol fuchsin is prepared by dissolving basic fuchsin in a solution of phenol and ethanol. The solution is then heated until it turns a deep red color.

Staining Procedure

In the Ziehl-Neelsen stain, the bacteria are first stained with carbol fuchsin. The slide is then washed with acid-alcohol, which decolorizes non-acid-fast bacteria. The slide is then counterstained with methylene blue, which stains the non-acid-fast bacteria blue.

In the Schaeffer-Fulton stain, the bacteria are first stained with malachite green, then decolorized and counterstained with carbol fuchsin, which stains the endospores red.

Safety

Carbol fuchsin is a potential skin irritant and should be handled with care. It is also flammable due to its ethanol content.

See Also

• Ziehl-Neelsen stain
• Acid-fast stain
• Mycobacteria
• Schaeffer-Fulton stain

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