KINETICS OF 2 GENETICALLY DISTINCT PNEUMOCYSTIS-CARINII POPULATIONS IN RAT COLONIES

The natural history of prototype and variant Pneumocystis carinii popu lations in several colonies of rats were monitored over time periods r anging from 1 to 4 years. Karyotypic profiles of organism populations from individual rats were evaluated for the proportion of prototype:va riant P. carinii and the number of animals harboring co-infections wer e enumerated. Throughout the observation periods: (1) each P. carinii population retained its distinctive karyotype; (2) the proportions of prototype:variant within the lungs fluctuated; and (3) the number of r ats co-infected within a colony varied. These surveys suggest a compet ition between 2 similarly adapted populations.