GENETIC AND IMMUNOLOGICAL CHARACTERIZATION OF THE MICROSPORIDIAN SEPTATA-INTESTINALIS CALI, KOTLER AND ORENSTEIN, 1993 - RECLASSIFICATION TO ENCEPHALITOZOON-INTESTINALIS

The relationships between the Encephalitozoon-like Septata intestinali s and other microsporidia that occur in humans, notably Encephalitozoo n cuniculi and Encephalitozoon hellem, is insufficiently documented us ing morphological descriptions alone. To assess mutual relationships, we have examined other phenotypic as well as genetic aspects of S. int estinalis, obtained both from tissue culture and clinical specimens, i n comparison with a number of other microsporidia. Phenotypic characte rization was performed by analysis of the protein composition and anti genic structure of Various microsporidian spores by SDS-PAGE and Weste rn blotting. The genetic characterization consisted of the determinati on of the sequence of the S. intestinalis rrs gene encoding the small subunit ribosomal RNA (srRNA), restriction fragment length polymorphis m (RFLP) analysis of amplified rrs genes and establishment of the degr ee of sequence identity between rrs genes of various microsporidian sp ecies. The unique sequence of rrs of S. intestinalis as well as the di stinct RFLP and SDS-PAGE profiles indicate that S. intestinalis is cle arly different from other human microsporidian species. However, its r rs gene shared about 90 % sequence identity with rrs of both Encephali tozoon spp., E. cuniculi and E. hellem. This is remarkably higher than the about 70 % identity observed between rrs of microsporidian specie s which belong to different genera and thus suggests that S. intestina lis should be regarded as a species of the genus Encephalitozoon. West ern blots revealed a marked cross-reactivity between S. intestinalis a nd both species of Encephalitozoon which also stresses the close relat ionship between these organisms. It is concluded that S. intestinalis is so closely related to E. cuniculi, the type species of Encephalitoz oon, that it should be reclassified as Encephalitozoon intestinalis.