Which staining technique is commonly used to demonstrate fungal elements in tissue sections?

• A. PAS
• B. Gram
• C. Acid-fast
• D. Hematoxylin and eosin

Answer: (A)

Demonstrating fungal elements relies on stains that highlight the carbohydrate-rich cell walls of fungi. The Periodic acid–Schiff (PAS) technique oxidizes sugars in these walls to aldehydes, which then react with Schiff reagent to produce a bright magenta color. That strong, specific signal makes fungi stand out clearly against the surrounding tissue, so PAS is routinely used when fungal infection is suspected in tissue sections.

Other stains target different organisms or are less specific for fungi. Gram staining in tissue is not as reliable for fungi in paraffin sections, acid-fast stains are aimed at mycobacteria, and hematoxylin and eosin is a general stain that often doesn’t make fungal elements as conspicuous. If glycogen could confound the PAS result, a diastase-treated PAS (PAS with diastase) can help distinguish glycogen from fungal walls, since glycogen is digested by diastase.