Metabolic and synthetic activities of Pneumocystis carinii in vitro

Pneumocystic carinii organisms obtained from the lungs of rats with glucocorticoid-induced pneumocystosis retained a number of metabolic activities during in vitro culture for 48 to 72 h. They were able to metabolize [14C]glucose to 14CO2, to synthesize proteins from 3H-amino acids, and to synthesize ribonucleic acid from [3H]uridine. Utilization of [14C]glucose was inhibitable by excess unlabeled glucose, mannose, fructose, 2-deoxy-D-glucose, iodoacetate, and pentamidine, but not glycerol or trimethoprim-sulfamethoxazole. Protein synthesis was almost completely inhibited by incubation with high concentrations of cycloheximide, pentamidine, suramin, and chloroquine, but not by rifampin, tetracycline, or gentamicin. In additional experiments, P. carinii organisms that had been incubated overnight in the presence of potentially lethal agents were tested for their ability to utilize [14C]glucose in inhibitor-free medium as a test of viability. Pentamidine, at concentrations which caused only modest inhibition of glucose metabolism, protein synthesis, amino acid transport, or ribonucleic acid synthesis, was lethal, whereas trimethoprim-sulfamethoxazole was not.