Pneumocystis carinii

The pneumonia by Pneumocystis carinii is common in immunocompromised patients (such as HIV-positive), usually presenting as bilateral pulmonary infiltrates on radiographs.
The organisms can be demonstrated in BAL material, as well as in bronchial washings and induced sputum.

With Papanicolaou stains, masses of organisms enmeshed in a proteinaceous material can be observed as green, foamy alveolar casts. The cysts are stained with silver stains; they are cup-shaped, 5-7 µm in diameter, often with a dark central zone. Giemsa stain the intracystic bodies or trophozoites as blue dots. The organisms can also be present in vacuolated macrophages. Direct immunofluorescence, performed on induced sputum, is very helpful.