Electron microscope studies of experimental Entamoeba histolytica infection in the guinea pig. I. Penetration of the intestinal epithelium by trophozoites.

Germ-free guinea pigs were inoculated intracecally with Entamoeba histolytica and the enteric flora derived from a human patient with acute amebic colitis. Aanimals were killed at post-inoculation intervals of 7 to 12 days. The mode of penetration of cecal epithelium by the ameba was examined by light and electron microscopy. The following sequence was reconstructed from numerous individual observations. When the amebae were in moderately close proximity to the brush, border, the microvilli became shortened, irregular, and sometimes disappeared. Dense material was observed between the amebae and microvilli. When the ameba was very close to the epithelium the apical portion of epithelial cytoplasm projected into the lumen contacting the organism, thus becoming detached from adjoining cells. This produced spaces between epithelial cells through which amebae invaded interepithelial spaces. Initially the ameba penetrated the interglandular epithelium. Later, it penetrated equally the glandular and interglandular epithelium barrier. There were marked alterations of cytoplasmic components of epithelial cells. Polymorphonuclear leukocytes migrated into the epithelium filling these spaces; these often showed a variety of degenerative processes. Amebae, utilizing their pseudopodia, moved further through the intercellular spaces and reached the lamina propria.