Table 1

Infectivity of cultured organisms

Inoculation sourcenOrganisms for first inoculation,* ×104Organisms for second inoculation, ×104Mean lung weights, gP. carinii × 105 per lung
Homogenate of infected frozen lung47.049.081.53  ±  0.153.38  ±  2.24
P. carinii from 15-day culture52.301.891.56  ±  0.184.23  ±  2.07
P. carinii from 62-day culture50.260.361.38  ±  0.131.01  ±  0.63
Saline control50.00.01.14  ±  0.140.0
  • * P. carinii cells were counted by microscopic examination (11). Homogenization of frozen lungs, rat immunosuppression to allow development of PCP, and P. carinii inoculation were as described (12). To avoid latent P. carinii infection commonly present in rats before immunosuppression, the test animals were treated for 3 weeks with the combination of trimethroprim and sulfamethoxazole (50 and 250 mg/kg, respectively). Two inoculations 3 days apart were used to reduce variations in the intensity of subsequent PCP. 

  • PCP causes an increase in lung weight due to the presence of the organisms, foamy exudate filling the alveoli, and inflammation, so that the degree of increased lung weight compared to the control reflects the degree of the pneumonia in the animal (12). Lung weights were taken at the time of sacrifice (27 days after the first inoculation). Values are given as mean ± SEM. 

  • Lung homogenates and P. carinii cell counts at the time of sacrifice were prepared as described (11).