ENTAMOEBA-DISPAR - ULTRASTRUCTURE, SURFACE-PROPERTIES AND CYTOPATHIC EFFECT

The cytological features of Entamoeba dispar, recently recognized by b iochemical 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 760RR clone A were more elongated in form, had a single frontal pseudopodium, and s howed a noticeable uroid. In sections of E. dispar trophozoites staine d with Toluidine blue, characteristic areas of cytoplasmic metachromas ia were seen due to the presence of large deposits of glycogen, seldom found in E. histolytica strain HM1:IMSS. Under the light microscope t he periphery of the nucleus in E. dispar was lined by finer, more regu larly distributed dense granules. With transmission electron microscop y the surface coat of E. dispar was noticeable thinner. In addition, E . dispar had a lower sensitivity to agglutinate with concanavalin A an d a higher negative surface charge, measured by cellular microelectrop horesis. The cytopathic effect of E. dispar was much slower analyzed b y the gradual loss of transmural electrical resistance of MDCK epithel ial cell monolayers mounted in Ussing chambers. Whereas in E. histolyt ica phagocytosis of epithelial cells plays an important role in its cy topathic effect, E. dispar trophozoites placed in contact with MDCK ce lls showed only rare evidence of phagocytosis. The results demonstrate that the morphology of E. dispar is different to that of E. histolyti ca, both at the light microscopical and the ultrastructural levels. In addition, they show that E. dispar in axenic culture has a moderate c ytopathic effect on epithelial cell monolayers. However, when compared to E. histolytica, the in vitro lytic capacity of E. dispar is much s lower and less intense.