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Intestinal Amoeba
Pathogenic vs. Non-pathogenic
- Pathogenic
- - Entamoeba histolytica
- - Blastocystis hominis
- Non-pathogenic
- - Entamoeba hartmanni
- - Entamoeba coli
- - Endolimax nana
- - Iodamoeba butschlii
- - Entamoeba polecki
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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).
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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
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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
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Single nucleus
Fine peripheral chromatin
Small central karyosome
Ingested RBCs distinguish E. histolytica from E. dispar
Entamoeba histolytica Trophozoites
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Nonpathogenic
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
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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.
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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
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Non-pathogenic
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
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Non-pathogenic
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.
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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
Infections with orgganisms that resemble both E. coli and E. histolytica should have E. polecki ruled out.
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Non-pathogenic
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
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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
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Trichrome Stained Trophozoite Flow Chart
Cells > 20μm
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Trichrome Stained Trophozoite Flow Chart
Cells < 20μm
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Trophozoite Size Comparison
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Trichrome Stained Cyst Flow Chart
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