Microscopy (page 2 of 3)

Nonpathogenic amebas (1)

A	B	C

A, B, C: Trophozoites of Entamoeba coli, line drawing (A) and trichrome stain (B, C).  The trophozoites each have one nucleus with characteristically a large, eccentric karyosome and coarse, irregular peripheral chromatin.  The cytoplasm is coarse and vacuolated ("dirty" cytoplasm) as illustrated in C.  Occasionally the cytoplasm contains ingested bacteria (B), yeasts or other materials.  The trophozoites of E. coli measure usually 20 to 25 µm, but they can be elongated (C) and reach up to 50 µm.

D	E	F	G

D, E, F, G: Cysts of Entamoeba coli, line drawing (D), wet mount in iodine (E), and trichrome stain (F, G).  Mature cysts typically have 8 nuclei, and measure usually 15 to  25 µm (range 10 to 35 µm).  The cyst in E shows 5 nuclei visible in this focal plane.  The cyst in G is an immature, binucleate form, frequently seen with E. coli, where a large glycogen vacuole pushes the nuclei to opposite sides.  Chromatoid bodies are seen less frequently than in E. histolytica.  When present they are usually splinter like with pointed ends (F) and thus different from the chromatoid bodies of E. histolytica, which have rounded ends.

H	I	J

H, I, J: Entamoeba hartmanni trophozoites, line drawing (H) and trichrome stain (I, J).  Entamoeba hartmanni is often called a "small histolytica" because these two species share many morphological characteristics, except their size.  The trophozoites of E. hartmanni (H, I, J) each have one nucleus with fine peripheral chromatin and a small, often centrally located karyosome.  The cytoplasm is finely granular.  Note that in I the trophozoite has ingested a yeast, not an erythrocyte.  (Ingestion of erythrocytes is pathognomonic of E. histolytica.)  Trophozoites of E. hartmanni measure usually 8 to 10 µm (range 5 to 12 µm ) and thus are smaller than those of E. histolytica (10 to 60 µm).

K	L

K, L: Entamoeba hartmanni cysts, line drawing (K) and trichrome stain (L).  Cysts of E. hartmanni when mature have 4 nuclei and elongated chromatoid bodies with rounded ends.  Cysts of E. hartmanni measure usually 6 to 8 µm (range 5 to 10 µm) and thus are smaller than those of E. histolytica (10 to 20 µm).