Entamoeba species
Entamoeba coli, cyst
Entamoeba coli is one of several non-pathogenic amebae that can be found in human stool specimens. It has both cyst and trophozoite forms. The cysts are relatively large, measuring 10 to 35 micrometers in diameter, and have 8 nuclei in their characteristic mature form. Cysts having anywhere from 1 to 16 nuclei may also be seen. The nuclei have the standard "Entamoeba-type" chromatin pattern, with a small karyosome (usually eccentric in E. coli) and a peripheral rim of condensed chromatin (so-called "dot and rim" pattern). The peripheral chromatin is often coarse and granular. The cytoplasm may contain glycogen and chromatoid bodies (usually with splintered ends).
Entamoeba histolytica, trophozoites, tissue
Entamoeba histolytica is the only proven pathogenic Entamoeba species. While it is often a commensal organism causing asymptomatic colonization, it can occasionally cause invasive disease resulting in dysentery, colitis, ameboma, ulceration, and disseminated disease (e.g. amebic liver 'abscess'). When invasive disease occurs, only the trophozoite stage is seen. In this case, trophozoites can be seen invading into the bowel wall (formalin fixed, paraffin-embedded tissue section, unknown stain). The arrows denote ingested red blood cells.
You can view whole slide images of Entamoeba histolytica in the colon HERE and a case in the liver HERE (H&E) and HERE (PAS).
Entamoeba histolytica/Entamoeba dispar, cysts
Cysts of Entamoeba histolytica/Entamoeba dispar typically measure 12 to 15 micrometers in diameter and have 1 to 4 small round nuclei. The nuclei have a 'ring and dot' chromatin pattern, with a small central karyosome and rim of condensed chromatin. The cytoplasm may contain chromatoid bodies which characteristically have rounded blunt ends.