Which stain is commonly used to visualize Pneumocystis jiroveci in tissue sections?

• A. Gram
• B. PAS
• C. Grocott
• D. Gridley

Answer: (C)

To visualize Pneumocystis jirovecii in tissue, you need a stain that highlights fungal cell walls with strong contrast. Grocott's methenamine silver stain is the standard because it binds silver to the fungal wall, turning Pneumocystis cysts dark against a pale background in alveolar spaces. This clear contrast makes detection easier even in the foamy exudate typical of Pneumocystis pneumonia. PAS can stain fungal elements, but it’s less specific for Pneumocystis and often gives more background staining; Gram stain targets bacteria and isn’t effective for visualizing Pneumocystis; Gridley stain isn’t the routine stain used for this organism. So, Grocott’s stain provides the most reliable visualization of Pneumocystis jirovecii in tissue sections.