Genetic and immunological characterization of the microsporidianSeptata intestinalisCali, Kotler and Orenstein, 1993: reclassification toEncephalitozoon intestinalis

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Abstract
SUMMARY: Th relationships between theEncephalitozoon-likeSeptata intestinalisand other microsporidia that occur in humans, notablyEncephalitozoon cuniculiandEncephalitozoon hellem, is insufficiently documented using morphological descriptions alone. To assess mutual relationships, we have examined other phenotypic as well as genetic aspects ofS. intestinalis, obtained both from tissue culture and clinical specimens, in comparison with a number of other microsporidia. Phenotypic characterization was performed by analysis of the protein composition and antigenic structure of various microsporidian spores by SDS-PAGE and Western blotting. The genetic characterization consisted of the determination of the sequence of theS. intestinalis rrsgene encoding the small subunit ribosomal RNA (srRNA), restriction fragment length polymorphism (RFLP) analysis of amplifiedrrsgenes and establishment of the degree of sequence identity betweenrrsgenes of various microsporidian species. The unique sequence ofrrsofS. intestinalisas well as the distinct RFLP and SDS-PAGE profiles indicate thatS. intestinalisis clearly different from other human microsporidian species. However, itsrrsgene shared about 90% sequence identity withrrsof bothEncephalitozoonspp.,E. cuniculiandE. hellem. This is remarkably higher than the about 70% identity observed betweenrrsof microsporidian species which belong to different genera and thus suggests that S.intestinalisshould be regarded as a species of the genusEncephalitozoon. Western blots revealed a marked cross-reactivity betweenS. intestinalisand both species ofEncephalitozoonwhich also stresses the close relationship between these organisms. It is concluded thatS. intestinalisis so closely related toE. cuniculi, the type species ofEncephalitozoon, that it should be reclassified asEncephalitozoon intestinalis.