Culture, electron microscopy, and immunoblot studies on a microsporidian parasite isolated from the urine of a patient with AIDS.

Microsporidian spores isolated from a urine sample of an HIV-positive patient were inoculated onto monolayers of six different cell cultures. The parasites (CDC:0291:V213) grew profusely in two of the cultures (HLF and E6) and extruded spores into the culture medium. The spores were Gram-positive, 2.25- to 2.8-microns long, 1.25- to 1.8-microns broad, and smooth-walled. Some of the spores had already extruded their polar tubes, which were either straight or slightly coiled. Infected host cells contained parasitophorous vacuoles filled with developing stages of the parasite, including mature spores. Each spore was surrounded by a thin, electron-dense exospore; a thick electron-lucent endospore; and a thin cell membrane. Cross-sections of six coils of the polar tube were seen inside the spore. Proteins extracted from spores of our isolate and those from Encephalitozoon cuniculi were separated on gradient sodium dodecyl sulfate-polyacrylamide gels and either silver-stained or transferred to nitrocellulose membranes. As many as 35 bands, ranging in molecular mass from 10,000 to 200,000, were visualized in the silver-stained gel. When reacted with the serum of our patient, strips cut from the membrane showed a number of bands ranging in molecular weight from 25,000 to 200,000. However, unique differences between the profiles of the two parasites were seen both in the immunoblot and the silver-stained protein profiles. Based on these findings, we conclude that our isolate belongs to the genus Encephalitozoon, but more studies are needed to identify our isolate to the species level.