Which stain demonstrates fungi such as Pneumocystis?

• A. Grocott's Methenamine Silver
• B. Hematoxylin & Eosin
• C. Immunohistochemistry
• D. Luxol fast blue

Answer: (A)

Staining fungi in tissue relies on methods that make the fungal cell wall stand out. Pneumocystis has a cell wall that reacts to silver-based stains, so the Grocott's methenamine silver method deposits silver on the fungal walls and turns them dark against a light background. This high-contrast visualization makes Pneumocystis organisms easy to spot in lung tissue, which is why this stain is the go-to for detecting fungi like Pneumocystis jirovecii.

Hematoxylin and eosin is general for tissue structure and can miss sparse fungal elements. Immunohistochemistry uses antibodies to detect fungi but is not the classic, routine demonstration method for Pneumocystis. Luxol fast blue targets myelin, not fungi.