Intestinal protozoa

Microbiology

• Protozoans are eukaryotic unicellular organisms that have organelles
• Many have a trophozoite form (active, motile), as well as a cyst form (vegetative)
• Stains:
  • Iron hematoxilin, which stains nuclei on a black background
  • Acid-fast stain, which highlights red Crypto/Cyclo/Iso
  • Can combine both of the above

Classification

From largest to smallest family

• Amoebae
  • Entamoeba histolytica/dispar (microscopically indistinguishable, but E. dispar is non-pathogenic)
  • Entamoeba harmanni and Entamoeba coli (non-pathogenic)
  • Endolimax nana
  • Iodamoeba butchlii
• Flagellates
  • Giardia lamblia
  • Dientamoeba fragilis (no cystic form)
  • Chilomastix mesnili
• Ciliates
  • Balantidium coli
• Coccidia: small, may be seen as acid-fast
  • Cryptosporidium species
  • Cyclospora cayetanensis
  • Cystoisospora belli (previously called Isospora)
  • Sarcocystis hominis
• Microsporidia

Approach to Microscopy

• Some have classic appearance:
  • Giardia trophs look like an owl
• Balantidium coli is huge
  • Trichomonas and Chilomastix trophs have flagellae and are tear-drop shaped
• Isospora belli looks like an eye or halved egg
  • Cyclospora is thick-walled and looks like a golf ball
• Cryptosporidium is the smallest (4-6 µm) and may have crescent-shaped sporozoites inside
  • Sarcocystis is quite large (15 µm), non-acid-fast, and looks like 2 joined ovals
• In order to differentiate the larger Amoebae, need to consider the size, nucleus characteristics, and other features
• What kind of nucleus is it?
  • Entamoeba: dark ing of peripheral chromatin, with a defined central nucleus and relatively clear perikarysomal space
  • Non-entamoeba: more blob-like, less well defined
  • Granulated: big dots, suggests Dientamoeba fragilis trophozoite
• How many nuclei?
  • Trophs are mostly mono-nucleated, cysts may be poly-nucleated
  • Dientamoeba has 2 nuclei in troph form
• What is the average size?
  • Need a measurement microscope
• Other stuff
  • Large vacuole suggests Iodamoeba butschlii
  • Uneven chromatin suggests E. coli
  • Chromatoidal bars suggests E. polecki, E. histolytica, or E. hartmanni

Organism	Nucleus type	No. nuclei	Size	Other features
E. histolytica	Entamoeba type	2-4	> 10 µm	Chromatoidal bars
E. coli	Entamoeba type	5-8+	> 10 µm
E. hartmanni	Entamoeba type		< 10 µm	Chromatoidal bars
E. polecki	Entamoeba type but 1/3 cell width		> 10 µm	Chromatoidal bars, but may have glycogen mass
Iodamoeba	Blob-like	1		Large vacuole
Endolimax	Blob-like	2-4