Microscopy

Trophozoites of Pneumocystis jirovecii are 1-5 µm, pleomorphic and contain a single nucleus.  Trophozoites are found in the lungs and many other extrapulmonary specimens, especially in immunocompromised patients.

A

A:  P. trophozoites in a bronchoalveolar lavage (BAL) specimen of an AIDS patient, stained with Giemsa.

Pneumocystis jirovecii cysts are thick-walled, rounded and approximately 5-8 µm in size, although thin-walled cysts exist also.  Cysts contain up to eight intracystic bodies.  Precysts have also been described for this organism.  Precysts are spherical, 4-7 µm in diameter and do not contain intracystic bodies (but may contain one or more nuclei).  Cysts are found in the lungs and many other extrapulmonary specimens, especially in immunocompromised patients.

B	C

B, C: Cysts of P. jirovecii in lung tissue, stained with methenamine silver and hematoxylin and eosin (H&E).  The walls of the cysts are stained black; the intracystic bodies are not visible with this stain.

D	E

D:  Indirect immunofluorescence using monoclonal antibodies against Pneumocystis jirovecii.
E:  Direct immunofluorescence antibody stain using monoclonal antibodies that target Pneumocystis jirovecii.  This image is from a bronchoalveolar lavage (BAL) specimen from a patient with a malignancy.  Image courtesy of Brigham & Women's Hospital, Boston, MA.