An improved method for the prolonged maintenance of Pneumocystis carinii in vitro.

A culture system for rat-derived Pneumocystis carinii was developed that allows the long-term maintenance of viable organisms in vitro. Organisms were derived from the lungs of immunosuppressed rats infected with P. carinii. P. carinii was maintained in culture with human embryonal lung (HEL) fibroblasts and Eagle MEM for up to 42 days. Passage of organisms was done by reinoculation of infected HEL cells with attached P. carinii onto a fresh monolayer of confluent cells. Rats pretreated with trimethoprim-sulfamethoxazole and inoculated with cultured organisms (up to day 42) developed P. carinii pneumonia by 6 weeks while control animals remained uninfected. P. carinii was able to be harvested from these lungs and reintroduced into tissue culture. Cultures have been maintained for up to 6 weeks without a substantial loss of P. carinii viability. In combination with intratracheal inoculation, this system raises the possibility of maintaining stable laboratory strains of P. carinii.