The use of a nested polymerase chain reaction for detecting Pneumocystis carinii from lung and blood in rat and human infection.

A nested polymerase chain reaction (PCR) assay was developed to detect both rat- and human-derived Pneumocystis carinii DNA. The nested PCR product was 125 bp long and was representative of part of the gene coding for the large subunit of mitochondrial ribosomal RNA. Twenty serial blood samples and 24 tissues from six immunosuppressed Sprague-Dawley rats were examined by nested PCR. All lung samples were positive by PCR and Toluidine blue O staining. Buffy coat samples and all the other tissues were PCR-negative during up to 6 weeks of immunosuppression. Thirty-five clinical bronchoalveolar lavage, induced sputum or tracheal aspirate samples from human patients were tested. Twelve of 35 were positive by both PCR and indirect fluorescence assay (IFA) and 19 of 35 were both PCR- and IFA-negative. Four of 35 were IFA-negative but PCR-positive and there were good responses in these patients to specific therapy, indicating that PCR may be more useful than IFA in clinical samples. P. carinii DNA was not detected in three blood samples. The nested PCR is a sensitive and specific DNA amplification method suitable for the routine diagnosis of P. carinii in human respiratory samples.