Microsporidia of the genus Encephalitozoon are emerging protozoal agents that mainly infect immunocompromised patients with AIDS. At present, disseminated infections with members of the genus Encephalitozoon can only be successfully treated with albendazole. As chitin is a basic component of the microsporidian spore. we evaluated, in vitro, the susceptibility of a human-derived strain of Encephalitozoon cuniculi to polyoxin D and nikkomycin Z, which are known competitive inhibitors of chitin synthetase enzymes. Using an in vitro assay, polyoxin D at 1, 10 and 100 microg/ml significantly reduced the number of parasitic foci on days 6, 9, and 15 post-infection. However, nikkomycin Z revealed a marked but lower reduction in the number of parasitic foci than polyoxin D. A significant reduction of parasitic foci was achieved for nikkomycin Z at 10 and 100 microg/ml up to day 9 post-infection. Polyoxin D was approximately tenfold more effective in our in vitro assay than nikkomycin Z.
