Flow cytometric analysis of microsporidia belonging to the genus Encephalitozoon

Flow cytometry analysis of Nosema species to assess spore viability and longevity

Nosema apis and Nosema ceranae are microsporidia which present resistant spores for the transmission stage (environmental spores) that play an important role for epidemiology and for laboratory studies of honey bee microsporidiosis. In this study, the long-term longevity of N. apis and N. ceranae spores exposed to 4 °C, room temperature (mean 25 °C) and 35 °C for 6-month long and to -20 °C for 10-month long has been assessed by flow cytometry. Storage temperature and the length of storage duration had adverse effects on spore viability of both Nosema spores, with significant differences between the two species. The greatest increase in spore mortality was observed in N. apis spores stored at 33 °C (64, 89%) and in N. ceranae spores at -20 °C (53.55%) and at 33 °C (51.97%). For N. ceranae spores at -20 °C, the loss in viability was very quick, getting an increase over 20% just after 6 days of exposure. Results on viability were confirmed by the infectivity tests where the lowest infectivity for N. ceranae was observed with spores stored for 10 months at -20 °C (79%; P < 0.05) and for N. apis with spores stored at 33 °C (71%; P < 0.05). For both Nosema species, the best storage temperatures were 25 and 4 °C, especially for N. apis that was almost unaffected at those temperatures.

Cytometric approach for detection of Encephalitozoon intestinalis, an emergent agent

Encephalitozoon intestinalis is responsible for intestinal disease in patients with AIDS and immunocompetent patients. The infectious form is a small spore that is resistant to water treatment procedures. Its detection is very important, but detection is very cumbersome and time-consuming. Our main objective was to develop and optimize a specific flow cytometric (FC) protocol for the detection of E. intestinalis in hospital tap water and human feces. To determine the optimal specific antibody (Microspor-FA) concentration, a known concentration of E. intestinalis spores (Waterborne, Inc.) was suspended in hospital tap water and stool specimens with different concentrations of Microspor-FA, and the tap water and stool specimens were incubated under different conditions. The sensitivity limit and specificity were also evaluated. To study spore infectivity, double staining with propidium iodide (PI) and Microspor-FA was undertaken. Distinct approaches for filtration and centrifugation of the stool specimens were used. E. intestinalis spores stained with 10 microg/ml of Microspor-FA at 25 degrees C overnight provided the best results. The detection limit was 5 x 10(4) spores/ml, and good specificity was demonstrated. Simultaneous staining with Microspor-FA and PI ensured that the E. intestinalis spores were dead and therefore noninfectious. With the stool specimens, better spore recovery was observed with a saturated solution of NaCl and centrifugation at 1,500 x g for 15 min. A new approach for the detection of E. intestinalis from tap water or human feces that ensures that the spores are not viable is now available and represents an important step for the prevention of this threat to public health.

Quantitation of microsporidia in cultured cells by flow cytometry

BACKGROUND

Microsporidia are obligate intracellular protozoan parasites that emerged as major opportunistic pathogens in humans since the onset of the AIDS pandemic. In the present study, we investigated whether FCM is a useful method for the quantitation of intracellular microsporidian spores in cultured cells.

METHODS

Microsporidia (Encephalitozoon cuniculi) were grown in cell cultures and various cell-lines were coincubated with microsporidian spores at different multiplicities of infection, as well as for different periods of time. After permeabilization of the cells, intracellular spores were stained with a polyclonal anti-E. cuniculi serum and a FITC-labeled secondary antibody. Stained cells were analyzed on a flow cytometer and results were compared with those of fluorescence microscopy.

RESULTS

Noninfected cells showed a lower fluorescence, while the relative fluorescence observed for infected cells was significantly higher. The cell population with the more intense fluorescence, representing cells with internalized microsporidian spores, increased with the multiplicity of infection as well as over time. Results of FCM and fluorescence microscopy were in excellent agreement for all experiments.

CONCLUSIONS

We have developed a flow cytometric assay to detect and quantify cells with intracellular microsporidian spores. This method is easy to use, highly reproducible, and should be useful for future research.

Purification of Enterocytozoon bieneusi spores from stool specimens by gradient and cell sorting techniques

A three-step method for the purification of Enterocytozoon bieneusi spores from stool specimens was developed. The primary process of purification of the spores from bacterial contaminants involved Percoll gradient centrifugation followed by additional separation using cesium chloride density gradient centrifugation. The cesium chloride-isolated spores were further purified using a flow cytometer with cell sorting capabilities. Sorting was performed without the use of antibodies, fluorochromes, or dyes, leaving the sorted spores in their native state, which appears to be less destructive for spores. When quantified by flow cytometry using tubes with known numbers of highly fluorescent polystyrene beads, the sorted material showed a slight decrease in light scatter characteristics compared with the slightly larger Encephalitozoon species spores. Although the overall recovery of the E. bieneusi spores was low, calcofluor and Gram chromotrope staining, indirect immunofluorescence assay, and transmission electron microscopy revealed that the sorted material was highly purified and contained large numbers of E. bieneusi spores and relatively few bacteria and other debris. The sorted material appeared to be sufficiently pure and could be used for in vitro culture and for the development of a variety of diagnostic reagents as well as in studying the genome of E. bieneusi and host-parasite interactions.

Identification and characterization of two subpopulations of Encephalitozoon intestinalis

Microsporidia are obligate intracellular protozoa that have been shown to be pathogenic to most living creatures. The development of in vitro cell culture propagation methods has provided researchers with large numbers of spores and facilitated the study of these organisms. Here, we describe heterogeneity within cell culture-propagated Encephalitozoon intestinalis suspensions. Flow cytometer histograms depicting the log side scatter and forward-angle light scatter of spores from nine suspensions produced over 12 months consistently showed two populations differing in size. The suspensions were composed primarily of the smaller-spore subpopulation (76.4% +/- 5.1%). The presence of two subpopulations was confirmed by microscopic examination and image analysis (P < 0.001). Small subpopulation spores were noninfectious in rabbit kidney (RK13) cell culture infectivity assays, while the large spores were infectious when inocula included > or = 25 spores. The small spores stained brilliantly with fluorescein isothiocyanate-conjugated monoclonal antibody against Encephalitozoon genus spore wall antigen, while the large spores stained poorly. There was no difference in staining intensities using commercial (MicroSporFA) and experimental polyclonal antibodies. Vital-dye (DAPI [4',6'-diamidino-2-phenylindole], propidium iodide, or SYTOX Green) staining showed the spores of the small subpopulation to be permeable to all vital dyes tested, while spores of the large subpopulation were not permeable in the absence of ethanol pretreatment. PCR using primers directed to the 16S rRNA or beta-tubulin genes and subsequent sequence analysis confirmed both subpopulations as E. intestinalis. Our data suggest that existing cell culture propagation methods produce two types of spores differing in infectivity, and the presence of these noninfective spores in purified spore suspensions should be considered when designing disinfection and drug treatment studies.

Flow cytometric detection of Leishmania parasites in human monocyte-derived macrophages: application to antileishmanial-drug testing

A flow cytometric technique was developed for detection of amastigotes of the protozoan Leishmania infantum in human nonadherent monocyte-derived macrophages. The cells were fixed and permeabilized with paraformaldehyde-ethanol, and intracellular amastigotes were labeled with Leishmania lipophosphoglycan-specific monoclonal antibody. Results showed that flow cytometry provided accurate quantification of the infection rates in human macrophages compared to the rates obtained by the conventional microscopic technique, with the advantage that a large number of cells could be analyzed rapidly. The results demonstrated, moreover, that labeling of intracellular amastigotes could reliably be used to evaluate the antileishmanial activities of conventional drugs such as meglumine antimoniate, amphotericin B, pentamidine, and allopurinol. They also established that various Leishmania species (L. mexicana, L. donovani) could be detected by this technique in other host-cell models such as mouse peritoneal macrophages and suggested that the flow cytometric method could be a valid alternative to the conventional method.

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 intestinalis 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, detect microsporidian spores in fecal smears and other clinical samples, they do not identify the species of microsporidia. A need for an easily performed test therefore exists. We reevaluated 120 stool samples that had been found positive for microsporidia previously, using the quick-hot Gram-chromotrope technique, and segregated them into two groups on the basis of spore size. 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 with bacteria, yeasts, or other structures in the stool samples was seen. Additionally, the numbers of spores that fluoresced in seven of these samples were substantially smaller than the numbers of spores that were present in the stained smears, indicating that these samples were probably derived from patients with mixed infections of Enterocytozoon bieneusi and E. intestinalis. Because a 1:400 dilution of this serum does not react with culture-grown Encephalitozoon hellem, Encephalitozoon cuniculi, or Vittaforma corneae or with Enterocytozoon bieneusi spores in feces, we concluded that an immunofluorescence test using this serum is a good alternative for the specific identification of E. intestinalis infections.