Intestinal Amoeba

  1. Intestinal Amoeba

    Pathogenic vs. Non-pathogenic
    • Pathogenic
    •  - Entamoeba histolytica
    •  - Blastocystis hominis

    • Non-pathogenic
    •  - Entamoeba hartmanni
    •  - Entamoeba coli
    •  - Endolimax nana
    •  - Iodamoeba butschlii
    •  - Entamoeba polecki
  2. Life cycle of Amoebas

    Cysts and trophozoites are passed in feces (1). Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool.
    Infection by Entamoeba histolytica occurs by ingestion of mature cysts (2) in fecally contaminated food, water, or hands. 
    Excystation (3) occurs in the small intestine and trophozoites (4) are released, which migrate to the large intestine. The trophozoites multiply by binary fission and produce cysts (5), and both stages are passed in the feces (1).
    Because of the protection conferred by their walls, the cysts can survive days to weeks in the external environment and are responsible for transmission. Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment.
    In many cases, the trophozoites remain confined to the intestinal lumen (A: noninvasive infection) of individuals who are asymptomatic carriers, passing cysts in their stool.  In some patients the trophozoites invade the intestinal mucosa (B: intestinal disease), or, through the bloodstream, extraintestinal sites such as the liver, brain, and lungs (C: extraintestinal disease), with resultant pathologic manifestations.
    Transmission can also occur through exposure to fecal matter during sexual contact (in which case not only cysts, but also trophozoites could prove infective).
    Image Upload 1
  3. Image Upload 2
    12 to 15 µm
    1 - 4 nuclei, depending on cyst maturity
    Centrally located karyosomes
    Fine peripheral chromatin
    Chromatoid bodies have round, blunt ends
    Entamoeba histolytica Cysts
  4. Image Upload 3
    Entamoeba histolytica Cysts

    • Right pic:
    •  - Trichrome stained Mature Cyst

    • Left pic:
    •  - Immature cyst
    •  - These tend to have a single nucleus, large vacuoles, and clumpy chromatin
  5. Image Upload 4

    Single nucleus
    Fine peripheral chromatin
    Small central karyosome
    Ingested RBCs distinguish E. histolytica from E. dispar
    Entamoeba histolytica Trophozoites
  6. Image Upload 5
    Looks the same as E. histolytica
    RBCs are NOT present in the cytoplasm
    Entamoeba dispar

    •  - Produces no intestinal symptoms
    •  - Not invasive
    •  - Chromotoid body with blunt rounded ends
  7. Non-pathogenic
    Same characteristics as E. histolytica but smaller
    Trophozoites measure 5-12 µm
    Cysts measure 5-10 µm
    Entamoeba hartmanni

    •  - Contaminated food and water.
    •  - Karyosome is usually smaller and more compact; also takes up a more delicate stain.
    •  - Nucleus may stain more darkly than E. histolytica.
    •  - Chromatin looks more like a solid ring (not beaded).
    •  - May contain bacteria but NOT RBCs.
  8. Image Upload 6

    More than 5 nuclei
    Immature cyst will have 2 nuclei
    Chromatoid bodies have pointed ends
    Vacuoles in cytoplasm
    Entamoeba coli Cysts

    •  - Largest
    •  - Measure 10-35 µm
    •  - If you see >5 nuclei it is E. coli
    •  - Usually easy to see in Iodine wet prep.
    •  - Usually round
  9. Image Upload 7

    Larger than E. histolytica
    Clumpy uneven peripheral chromatin
    Large eccentric karyosome
    Ingests bacteria, fungus, etc.
    Entamoeba coli Trophozoites

    •  - Measure 15-50 µm
    •  - Worldwide distribution: warmer climates, primitive hygienic conditions
  10. Image Upload 8

    Same size range as E. hartmanni
    Cyst always has 4 nuclei
    Large karyosomes
    No peripheral chromatin
    Endolimax nana

    •  - Cysts measure 5-10 µm
    •  - Trophs measure 6-12 µm
    •  - Differs from E. hartmanni by the large karyosome and no peripherial chromatin
    •  - Worldwide distribution: warm moist climates, areas with lower standard of sanitary conditions.
    •  - Contaminated food and water
    •  - Perm stain best way for ID.
  11. Trophozoites measure 10-25 µm
    Cysts measure 9-24 µm
    Peripheral chromatin is usually delicate
    Karyosome is pleomorphic in cysts; cysts are usually uninucleate
    Associated with pigs and primates
    Entamoeba polecki

    • Left and middle:
    •   - cysts: note the pleomorphic cytoplasmic inclusions

    • Right:
    •   - troph

    Infections with orgganisms that resemble both E. coli and E. histolytica should have E. polecki ruled out.
  12. Image Upload 9

    No peripheral chromatin
    Achromatic granules
    Cyst always contains glycogen vacuole
    Iodamoeba butschlii

    •  - Achromatic granules can appear around the nucleus.
    •  - 8 – 20 um
    •  - Worldwide distribution: warm moist climates, poor sanitation, low standard of personal hygiene
    •  - Granular cytoplasm (vacuoles with debris/bacteria)
    •  - Large karyosome
    •  - 1 nucleus
  13. Image Upload 10

    Pathogenic in large numbers
    Part of normal flora
    Large central vacuole surrounded by multiple small nuclei
    Classification as an amoeba under review
    Blastocystis hominis

    • Can cause diarrhea, cramps, nausea, fever, vomiting, abdominal pain, urticaria (hives)
    • Fecal – Oral
    • Common in humans and animals worldwide

    • 4 forms:
    •   - Cyst: thin and thin walled forms
    •   - Central Vacuole Form: most commonly seen (can occupy most of the cell)
    •   - Ameoboid form: rarely seen
    •   - Granular form: seen in cultures
  14. Trichrome Stained Trophozoite Flow Chart

    Cells > 20μm
    Image Upload 11
  15. Trichrome Stained Trophozoite Flow Chart

    Cells < 20μm
    Image Upload 12
  16. Trophozoite Size Comparison
    Image Upload 13
  17. Trichrome Stained Cyst Flow Chart
    Image Upload 14
  18. Wet Prep Cyst Flow Chart
    Image Upload 15
  19. Cysts Size Comparison
    Image Upload 16
Card Set
Intestinal Amoeba
Intestinal Amoeba lecture notes