Protozoa

Common protozoa easily recognized on microscopy include:
(A) Entamoeba histolytica (trichrome stain)
(B) Giardia lamblia (wet mount)
(C) Cryptosporidium (acid-fast stain)
(D) Cystoisospora (wet mount with exposure to ultraviolet light)
(E) Cyclospora (wet mount)
(F) Balantidium coli (wet mount with iodine)
E. histolytica may appear as a cyst form with chromatid bar (A). Giardia lamblia has distinctive flagella (B). Cryptosporidium is small with acid-fast staining (C). Cystoisospora (formerly Isospora) has an oblong shape, one or two nuclei, natural fluorescence, and acid-fast positivity (D). Cyclospora is similar to but larger than Cryptosporidium, with natural fluorescence and acid-fast positivity (E). Balantidium coli is the largest protozoan infecting humans and the only ciliate (F).
The measurements given represent the range seen for the black bar lengths for each organism.