Aims-To assess the reliability of the detection of erythrophagocytic amoebic trophozoites in stool samples in the diagnosis of dysentery associated with invasive Entamoeba histolytica. Methods--Amoebic culture was carried out on single stool samples collected from patients from Mexico, Colombia, and Bangladesh. The stools had been examined by light microscopy. Amoebic dysentery was diagnosed when erythrophagocytic E histolytica trophozoites were observed in a case of bloody diarrhoea. E histolytica isolates were characterised by isoenzyme electrophoresis and results correlated with microscopical findings in stools. Statistical analysis was performed using the x2 test. Results-Where erythrophagocytic amoebae had been observed in dysenteric stool specimens the E histolytica phenotype was invariably invasive (p < 0*0001). Observation of erythrophagocytic amoebae in dysentery is 100% specific and predictive of infection with invasive E histolytica. When amoebic culturepositive cases only are considered it is 96% sensitive. In this study E histolytica of zymodeme XIV was more commonly associated with amoebic dysentery than zymodeme II. There was no significant difference between the carriage rate of invasive and non-invasive E histolytica in non-dysenteric diarrhoea. Asymptomatic subjects carried non-invasive E histolytica more frequently than invasive E histolytica. Patients with non-amoebic dysentery, when shown to be infected with E histolytica, carried non-invasive strains (12%

The cytological features of Entamoeba dispar, recently recognized by biochemical and molecular biology criteria as a distinct species, were compared to those of Entamoeba histolytica When cultured under axenic conditions, living trophozoites of E. dispar strain SAW 76ORR clone A were more elongated in form, had a single frontal pseudopodium, and showed a noticeable uroid. In sections of E. dispar trophozoites stained with Toluidine blue, characteristic areas of cytoplasmic metachromasia were seen due to the presence of large deposits of glycogen, seldom found in E. histolytica strain HM1:IMSS. Under the light microscope the periphery of the nucleus in E. dispar was, lined by finer, more regularly distributed dense granules. With transmission electron microscopy the surface coat of E. dispar was noticeable thinner. In addition. E. dispar had a lower sensitivity to agglutinate with concanavalin A and a higher negative surface charge, measured by cellular microelectrophoresis. The cytopathic effect of E. dispar was much slower, analyzed by the gradual loss of transmural electrical resistance of MDCK epithelial cell monolayers mounted in Ussing chambers. Whereas in E. histolytica phagocytosis of epithelial cells plays an important role in its cytopathic effect. E. dispar trophozoites placed in contact with MDCK cells showed only rare evidence of phagocytosis. The results demonstrate that the morphology of E. dispar is different to that of E. histolytica, both at the light microscopical and the ultrastructural levels. In addition they show that E. dispar in axenic culture has a moderate cytopathic effect on epithelia] cell monoLayers. However, when compared to E. histolytica, the in vitro lytic capacity of E. dispar is much slower and less intense.

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ABSTRACT. An important aspect of the biology of Naegleria sp. is the differentiation processes that occur during encystation and excystation. We studied these using both fluorescence and transmission electron microscopy techniques. In the initial stages of encystation, the cisternae of the endoplasmic reticulum became densely filled with a fibrillar material. Vesicles with a similar content that appeared to be derived from the cisternae were also observed in close contact with the plasma membrane. As encystation progressed, the fibrillar material became localized on the surface of the amoeba. An irregular compaction was observed in some areas of the cyst wall, which contained thin extensions of the cyst wall fibrillar material. Completely formed cysts had two to three ostioles, each sealed by an operculum. The operculum contained two areas in which a differential compaction of the fibrillar structure was observed. When excystation was induced, small dense granules (DGs), which were in close contact with fibrillar material were observed in the cyst cytoplasm and in the peritrophic space. During excystation, the more compact component of the operculum moves to enable the pseudopod of the emerging trophozoite to penetrate the ostiole. Vacuoles containing a fibrillar material, probably derived from the cyst wall, were observed in the cytoplasm of the pseudopodia. Our results provide a platform for further studies using biochemical markers to investigate the origin of the cyst wall as well as the role of DGs during excystation in Naegleria.