Detection by an immunofluorescence test of Encephalitozoon intestinalis spores in routinely formalin-fixed stool samples stored at room temperature

Of the several microsporidia that infect humans, Enterocytozoon bieneusi is known to cause a gastrointestinal disease whereas Encephalitozoon intestin alis causes both a disseminated and an intestinal disease. Although several different staining techniques, including the chromotrope technique and its modifications, Uvitex 2B, and the quick-hot Gram-chromotrope procedure, de tect microsporidian spores in fecal smears and other clinical samples, they do not identify the species of microsporidia. A need for an easily perform ed test therefore exists. We reevaluated 120 stool samples that had been fo und positive for microsporidia previously, using the quick-hot Gram-chromot rope technique, and segregated them into two groups on the basis of spore s ize. We also screened the smears by immunofluorescence microscopy, using a polyclonal rabbit anti-E. intestinalis serum at a dilution of 1:400. Spores in 29 (24.1%) of the 120 samples fluoresced brightly, indicating that they were E. intestinalis spores. No intense background or cross-reactivity wit h bacteria, yeasts, or other structures in the stool samples was seen. Addi tionally, the numbers of spores that fluoresced in seven of these samples w ere substantially smaller than the numbers of spores that were present in t he stained smears, indicating that these samples were probably derived from patients with mixed infections of Enterocytozoon bieneusi and E. intestina lis. Because a 1:400 dilution of this serum does not react with culture-gro wn Encephalitozoon hellem, Encephalifozoon cuniculi, or Vittaforma corneae or with Enterocytozoon bieneusi spores in feces, we concluded that an immun ofluorescence test using this serum is a good alternative for the specific identification of E. intestinalis infections.