Soluble-protein and antigenic heterogeneity in axenic Blastocystis hominis isolates: pathogenic implications

The protein profile and the antigenic cross-reactivity of 18 axenic isolates of Blastocystis hominis obtained from symptomatic patients with chronic diarrhea (14 isolates) showing no evidence of parasitic etiology and from patients with acute diarrhea attributable in 2 cases to Salmonella spp. were analyzed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of soluble proteins showed the existence of a common profile composed of 31 bands, with molecular weights ranging between 24 and >200 kDa, and minor differences in the proteins of 149, 118, 106, 50, 48, 47, and 30 kDa. These differences allowed us to classify the strains into three related patterns (I-III). In an indirect immunofluorescence assay, all strains were serologically identical, but two related antigenic groups (1 and 2) were found in double-immunodiffusion and Western-blot studies. The isolates of protein patterns I and II belonging to antigenic group 1 were isolated from patients with chronic diarrhea, whereas the four isolates from patients with acute diarrhea were clustered in protein pattern III and in antigenic group 2. These results confirm the protein and antigenic heterogeneity of B. hominis and the existence of demes with different pathogenic roles.

In vitro encystation of Blastocystis hominis: a kinetics and cytochemistry study

The kinetics of in vitro encystation of Blastocystis hominis was studied over 9 days. The differentiation between trophic (TF) and cyst forms (CF) was determined by differential counts before and after treatment with distilled water. A cytochemistry study using acridine orange and Calcofluor white wet-mount preparations of CF was carried out. The growth curves of TF and CF were related because the decrease in TF was followed by an increase in CF, and vice versa. The maximum of CF counts was obtained on the 6th or 7th day. Using the differential acridine orange stain, two subpopulations of CF, yellow-orange fluorescent cells or precysts and green fluorescent cells or cysts, were detected and their curves were also related. CF was stained by Calcofluor white, which suggested the existence of beta-(1-4)-glycosyl residues in the wall cysts of B. hominis.

Karyotypic diversity among Blastocystis hominis isolates

Fifteen Blastocystis hominis strains, 13 axenic and 2 monoxenic, have been included in the present study. The chromosomal pattern was analyzed by the contour-clamped homogeneous electric-field (CHEF) system. The number of chromosomes detected ranged between 9 and 13, with sizes from 2200 kbp to 260 kbp. Eleven karyotypic profiles, with a common pattern constituted by 8 chromosomes of 2200, 1280, 890, 840, 700, 650, 540 and 260 kbp, were observed. The Jaccard index demonstrated that the similarity between isolates ranged from 0.5714 to 1. The different isolates were clustered in 3 karyotypes (A: 8 isolates; B: 6 isolates and C: 1 isolate). All isolates grouped in karyotype A presented a characteristic band of 730 kbp, whereas in the isolate of karyotype C the 810-kbp band was not observed.

[Clinical significance of Blastocystis hominis infection: epidemiologic study]

BACKGROUND

To evaluate the frequency of Blastocystis hominis parasitation and to ascertain its role as an intestinal a prospective study during 18 months pathogen has been carried out.

SUBJECTS AND METHODS

The study included 2,039 patients, which were classified in three groups (asymptomatic [group A], with suspicion of parasitosis [group B], with diarrhoea [group C]). In all cases a coproparasitological study was performed. In the group C the presence of non-parasitic enteropathogens was also investigated. In patients with B. hominis in the absence of other pathogens clinical and epidemiological characteristics were evaluated. Also, its was determined the morphology and quantification of parasites.

RESULTS

Parasites were identified in 26.2% of population. B. hominis was identified in 336 patients (16.5%). The frequency of parasitation was superior in adults (p < 0.0001), with a slight predominance in the female sex. The rate of asymptomatic carriers was 3.3%. In 21 patients B. hominis (group C) was observed in absence of other enteropathogens. Statistical significant association was found between B. hominis, in absence of other pathogens and the presence of clinical manifestations (p < 0.0001), the most common of which were diarrhoea and abdominal pain. We did not find a statistically significant association between the number of B. hominis present and stool characteristics. The vacuolar form was the predominant morphological type. The ameboid form was observed only in diarrhoeal stools.

CONCLUSIONS

B. hominis is the most frequent parasite found in faecal parasitological investigation. In absence of other causes, B. hominis must be considered as a pathogen.

Description of an improved method for Blastocystis hominis culture and axenization

An improved method for Blastocystis hominis culture and axenization was developed in the present study. Stool samples were cultured in prereduced Boeck-Drbohlav NHI modified medium (with several modifications) supplemented with antibiotics (0.4% ampicillin, 0.1% streptomycin, 0.0006% amphotericin B). Axenization was performed by the combination of partial purification of B. hominis by Ficoll-metrizoic acid gradient and inoculation in fresh medium containing active antibiotics against remaining bacteria. A total of 25 strains were obtained by this procedure. The time required for axenization ranged between 3 and 5 weeks. The generation time of axenic strains ranged from 6.6 to 12.1 h (mean +/- SD 110.0 +/- 1.8 h) and the mean number of generations was 2.5 +/- 0.6 h per 24 h. The size of vacuolar and ameboid forms found in stools and in culture was similar. The special formulation of the medium used reduced the generation time and did not modify the cellular size as compared with fecal forms.

Identification of surface coat carbohydrates in Blastocystis hominis by lectin probes

The carbohydrate residues of the surface coat of 20 axenic cultures of Blastocystis hominis were studied using FITC-labelled lectins (ConA, WGA, DBA, HPA, SBA, PNA, UEAI and LPA). The specific affinity of reactive lectins was determinated by competitive inhibition assay with specific carbohydrates or by enzymatic pre-treatment of cells. All stocks strongly bound ConA and HPA; WGA, UEAI and LPA were partially reactive, and the remaining lectins were nonreactive. Inhibition assays showed abolition (WGA, LPA, UEAI and HPA) or partial reduction (ConA) of lectin affinity, which demonstrated the specificity of binding assay. These results indicate that B. hominis has surface components containing alpha-D-mannose, alpha-D-glucose, N-acetyl-alpha-D-glucosamine, alpha-L-fucose, chitin and sialic acid.