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Cysts of Entamoeba invadens obtained under axenic conditions were stained with wheat germ agglutinin labelled with colloidal gold. Microscopic observation of encysting cultures revealed that upon staining, cysts acquired a red coloration, while trophozoites remained unstained. E. histolytica and E. coli cysts obtained from asymptomatic patients were also stained red by this technique. Electronmicroscopic examination of stained cells showed a layer of colloidal gold granules attached to the surface of cysts, while trophozoites remained free of gold granules. The results of the staining procedure developed, agreed with the known facts that wheat germ agglutinin is a lectin that binds specifically to chitin and its oligomers, and that chitin is present in the cyst wall of E. invadens. The results suggested that chitin is also present in the wall of cysts of E. histolytica and E. coli.

The ultrastructure of the wall of E. invadens cysts induced in axenic cultures was compared by transmission electron microscopy of thin sections, with that of E. histolytica and E. coli cysts obtained from feces of human asymptomatic carriers. The cyst wall of the three species studied had similar ultrastructural features; in all, the wall was composed mainly by the aggregation of filaments adjacent to the plasma membrane. The cytoplasmic components which might be involved in the synthesis and deposit of the cyst wall of E. invadens appear to be different to those of E. coli and E. histolytica cysts.

The degree of eythrophagocytosis of two recently isolated strains of E. histolytica was measured by microscopic examination. Amebas isolated from a patient with amebic rectocolitis (strain HM22:IMSS, monoxenic) ingested human red blood cells faster and in larger numbers than trophozoites isolated from an asymptomatic carrier (HM27:IMSS, monoxenic). The results suggest that an increased rate of phagocytosis could be one of the surface properties characteristic of the invasive strains of E. histolytica.

Mixed and monoxenic cultures of rectal exudates from three patients with amebiasis of colon, and of feces from three asymptomatic carriers of Entamoeba histolytica obtained after administration of a saline cathartic, and from a case of exudate of the perianal cutaneous lesion border produced by this parasite, were done. The culture media used were for: mixed culture, Boeck and Drbohlav modified culture and, for monoxenic culture, Diamond's monophasic TP-S-1 medium without vitamin mixture and using bovine serum. In order to inhibit the bacterial growth in the mixed culture, streptomycin sulphate and pencillin G were used. In order to eliminate the bacterial flora kanamicin sulphate, chloramphenicol, gentamycin and disodic carbenicillin were added. Mixed cultures of seven strains of Entamoeba histolytica were obtained: HM22:IMSS, HM23:IMSS, HM24:IMSS, HM26:IMSS, HM27:IMSS, HM28:IMSS y HM29:IMSS, and monoxenic culture with Bacteroids symbiosus of the strains HM22:IMSS and HM27:IMSS, with a previous adaptation in mixed culture. The adaptation of HM26:IMSS strain in monoxenic culture was obtained by means of direct seeding of the rectal exudate with Fusobacterium symbiosus.