GENETIC DIVERSITY IN HUMAN-DERIVED PNEUMOCYSTIS-CARINII ISOLATES FROM4 GEOGRAPHICAL LOCATIONS SHOWN BY ANALYSIS OF MITOCHONDRIAL RIBOSOMAL-RNA GENE-SEQUENCES

The opportunistic fungal pathogen Pneumocystis carinii is a frequent c ause of pneumonia in immunocompromised hosts. In this study, we have c ompared the DNA sequences of a portion of the mitochondrial large-subu nit rRNA gene of P. carinii (an informative locus showing up to 27% di fferences among isolates of P. carinii from human-, rat-, mouse-, ferr et-, rabbit-, and horse-infected lungs) obtained from human-derived is olates from widely disparate geographical areas, including Britain, th e United States, Brazil, and Zimbabwe. A single-base polymorphism whic h varied among samples was identified. Apart from this nucleotide, the DNA sequences of all samples were identical. The sequences of the Bri tish samples were shown to be stable over a period of 4 years. These d ata suggest that there is relatively low genetic diversity among isola tes of human-derived P. carinii from different global regions.