Discrimination of rat-derived Pneumocystis carinii f. sp. Carinii and Pneumocystis carinii f. sp. Ratti using the polymerase chain reaction.

The rat model of Pneumocystis carinii infection is widely used for the study of this non-culturable pathogen. Two genetically divergent <<special forms>> of the organism have been detected in infected rat lungs, P. carinii formae specialis carinii and P. carinii formae specialis ratti, in some cases as a co-infection. We have developed a simple and rapid method to analyse rat-derived P. carinii samples, based on DNA amplification of a portion of the gene encoding the mitochondrial large subunit ribosomal RNA. A pair of oligonucleotide primers were designed for each special form of rat-derived P. carinii, the RC primer pair amplifying a 137 bp fragment from P. carinii f. sp. carinii DNA and the RR primer pair amplifying a 251 bp fragment from P. carinii f. sp. ratti DNA. The specificity of the primers was confirmed by sequencing the amplification products. The polymerase chain reaction (PCR) technique was consistent with, and more sensitive than, the electrophoretic karyotype method. The application of the specific PCR technique has implications for future studies on epidemiology, drug sensitivity, immunology and molecular biology of rat-derived P. carinii.