Pathogenic action of Entamoeba invadens: intestinal epithelium invasion by trophozoites in vitro.

Interactions between live Entamoeba invadens trophozoites and guinea-pig caecal explants were studied. A high percentage of amoebae adhering to the apical surface of epithelial cells was observed 10-20 min after infection, but no histopathological changes were observed. After 30 min, mild oedema at the base of the interglandular epithelium and death of some epithelial cells were evident. The epithelial barrier was invaded by amoebae at desquamating zones and phagocytosis of epithelial cells or cellular debris was occasionally observed. Invasion of the mucosa and tissue necrosis became more severe with increased time of incubation. The continuity of epithelial lining was severely compromised after 2 h of infection and erosive lesions were prominent in the mucosa. These results demonstrate that E. invadens is able to invade the intestinal epithelium although it reportedly lacks the powerful cytotoxic and cytolytic elements described for E. histolytica.

Quantitative evaluation of intracellular degradation in Entamoeba invadens.

A quantitative study on digestion of erythrocytes by Entamoeba invadens was attempted. Trophozoites of the IP-1 strain were fed red blood cells for 30 min, and subsequently phagocytosis was stopped by means of osmotic shock; post-phagocytosis incubations for up to 15 h were made in order to evaluate intracellular digestion, after staining the red blood cells with benzidine. Eighty-two per cent of trophozoites were capable of phagocytosing erythrocytes, containing an average of 5.5 erythrocytes per amoeba. Erythrocyte digestion within amoebae was shown by loss of benzidine-stainable material and proceeded with a first-order kinetics, with a t1/2 approximately 7 h. Within 15 h there were no amoebae containing erythrocytes. The procedure described may be useful for the evaluation of intracellular digestion in other Entamoeba species.