Which method is used for demonstration of fungi in tissue sections?

• A. PAS
• B. Giemsa
• C. Gram
• D. Ziehl-Neelsen

Answer: (A)

Staining that highlights the carbohydrate-rich cell walls of fungi is most effective for showing them in tissue sections. The Periodic acid-Schiff (PAS) method oxidizes polysaccharides in fungal walls to form aldehydes, which then react with Schiff reagent to give a bright magenta color. This makes fungal elements like hyphae and yeasts stand out clearly against the surrounding tissue in paraffin-embedded sections. Sometimes diastase digestion is used to remove glycogen background and sharpen fungal visibility.

Other stains serve different purposes: Giemsa is commonly used for smears and certain parasites, Gram stain emphasizes bacterial morphology (and fungi can be variably stained), and Ziehl-Neelsen targets acid-fast bacteria. That makes PAS the most suitable choice for demonstrating fungi in tissue sections.