Demonstration and determination of DNA in Pneumocystis carinii by fluorescence microscopy with 4', 6-diamidino-2-phenylindole (DAPI).

We have attempted to demonstrate DNA and to measure the amount of nuclear DNA in Pneumocystis carinii by fluorescence microscopy with 4', 6-diamidino-2-phenylindole (DAPI). Due to the high specificity of DAPI for DNA, only nuclei and mitochondria were stained. An uninucleate trophozoite and a mature cyst containing eight intracystic bodies were distinguished easily each other after staining with DAPI. The total amount of nuclear DNA of eight intracystic bodies in a cyst was approximately eight times that of the small type of trophozoite. When nuclei of uninucleate trophozoites were randomly examined, the distribution pattern of nuclear fluorescence intensity showed two peaks, one at 1C and the other at 2C. Moreover, it showed also a gradual transition in DNA values from 1C to 2C, and very few nuclei with polyploid DNA values. The primary advantage of this method with DAPI is that it allows a more efficient evaluation of the life cycle of P. carinii.