Improved intracellular morphology of Pneumocystis carinii from rat lung by postfixation with a mixture of potassium ferrocyanide and osmium tetroxide.

Pneumocystis carinii infected rat lungs were postfixed with a mixture of OsO4 and K4Fe(CN)6. A marked improvement in staining of cell membranes, endoplasmic reticulum, nuclear membranes and glycogen was observed. These improvements were seen in both the trophic and cystic forms of the organisms. The addition of K4Fe(CN)6 did not improve the staining of cell walls, microtubules or ribosomes. Trophozoites were seen attached to both type 1 and type 2 pneumocytes by filopodia and/or intercalation of the cell body of P. carinii with the host lung cells. It is expected that the improvement in ultrastructural detail will allow better understanding of the ultrastructure of P. carinii and provide insights into the modes of action of various antimicrobial compounds on this organism.