What stain will demonstrate Pneumocystis jiroveci?

• A. PAS
• B. Grocott
• C. Gridley
• D. Auramine-rhodamine

Answer: (B)

Pneumocystis jiroveci is a fungal organism, and visualizing it relies on staining methods that highlight fungal cell walls with strong contrast. The Grocott methenamine silver stain uses a silver impregnation reaction that binds to the polysaccharide components of fungal walls, turning the organism’s cyst walls black against a lighter green or contrasting background. This creates a sharp, easily identifiable image of Pneumocystis cysts in lung tissue or bronchoalveolar lavage samples, which is why this stain is the standard choice for detecting P. jiroveci.

PAS can also stain fungal elements because it highlights carbohydrates in the cell wall, but Grocott’s stain provides superior specificity and contrast for Pneumocystis cysts, making it more reliable for diagnosis. The other stains shown target different things: Auramine-rhodamine is used for acid-fast organisms (like Mycobacteria) and is not a dependable method for Pneumocystis; Gridley stain is not the preferred method for visualizing Pneumocystis in routine practice.