A silver methenamine stained slide of a bronchial washing from an AIDS patient is examined. Which organism is most likely identified?

A silver methenamine stained slide of a bronchial washing from an AIDS patient is examined. Which organism is most likely identified?

• A. Pneumocystis jiroveci
• B. Candida albicans
• C. Histoplasma capsulatum
• D. Cryptococcus neoformans

Answer: (A)

Gomori methenamine silver staining of a respiratory specimen highlights Pneumocystis jirovecii by staining its cyst walls dark, producing small round to cup-shaped bodies about 5–8 microns. In an AIDS patient, this pattern is classic for Pneumocystis pneumonia, making Pneumocystis jirovecii the most likely identification in a silver-stained bronchial washing. Other fungi would show different forms on this stain or require different stains to visualize their characteristic features—Candida would appear as budding yeast with pseudohyphae, Histoplasma as small intracellular yeasts within macrophages, and Cryptococcus as encapsulated yeasts (best seen with capsule-specific stains). Thus the distinctive cysts on GMS in this clinical setting point to Pneumocystis jirovecii.

Gomori methenamine silver staining of a respiratory specimen highlights Pneumocystis jirovecii by staining its cyst walls dark, producing small round to cup-shaped bodies about 5–8 microns. In an AIDS patient, this pattern is classic for Pneumocystis pneumonia, making Pneumocystis jirovecii the most likely identification in a silver-stained bronchial washing. Other fungi would show different forms on this stain or require different stains to visualize their characteristic features—Candida would appear as budding yeast with pseudohyphae, Histoplasma as small intracellular yeasts within macrophages, and Cryptococcus as encapsulated yeasts (best seen with capsule-specific stains). Thus the distinctive cysts on GMS in this clinical setting point to Pneumocystis jirovecii.