An ELISA method for quantitation of Pneumocystis carinii in culture and lung

Numbers of Pneumocystis carinii in cultures or tissues traditionally have been determined by counting organisms on Giemsa-stained slides. For cultures, 10 microliters of culture supernatants have been sampled and counted on days 1, 3, 5 and 7. Infectivity scores of P. carinii-infected animal lung have been determined by three examiners scoring lung impression smears stained with Giemsa using a roughly logarithmic scale. Both counting procedures are tedious and time consuming. We have developed an enzyme-linked immunosorbent assay (ELISA) system which uses culture supernatants (in vitro) or homogenized animal lung (in vivo) as antigen, convalescent rat sera as primary antibody, and goat anti-rat alkaline phosphatase-conjugated immunoglobulin G as secondary antibody. The ELISA method shows good correlation with manual counts of Giemsa stains and allows a more rapid, more efficient method for quantitating P. carinii in both culture and infected lung.