Typing of Pneumocystis carinii f. sp hominis by PCR-SSCP to indicate a high frequency of co-infections

Broncho-alveolar lavage specimens from patients with Pneumocystis carinii p neumonia were investigated by PCR-single strand conformation polymorphism ( SSCP) analysis of four genomic regions for P. carinii f. sp. hominis. In al l, 32% of specimens produced two bands (one allele) for each of the four ge nomic regions, suggesting an infection with a single P.c. hominis type. The other specimens displayed more than two bands for at least one of the four genomic regions, suggesting several theoretical possibilities: co-infectio ns, heterozygosity of diploid or polyploid organisms, or multicopy genes. Q uantification of the different alleles and analysis of mixtures of specimen s showed that different alleles of a genomic region were most often present in different proportions in a given specimen, In contrast, experiments wit h plasmid insertion of two alleles resulted in the detection of identical p roportions of the two alleles, This suggests that neither heterozygosity of diploid organisms nor multicopy genes are responsible for the presence of two alleles. Unequal proportions are most likely explained by the occurrenc e of co-infections. The putative co-infecting types could be identified in the majority of specimens.