Questions and Answers
Which species of amebae are pathogenic?
What is the mode of transmission for Entamoeba histolytica?
Entamoeba histolytica is the only member of the family Entamoebidae to cause colitis.
True
What are the sizes of E. histolytica trophozoites?
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E. histolytica trophozoites multiply by ______.
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What characterizes E. histolytica cysts?
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Which of the following is NOT a characteristic of E. histolytica?
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What is the characteristic shape of E. histolytica chromatoidal bars?
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E. histolytica has organelles resembling mitochondria.
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Study Notes
Intestinal Amebae Overview
- Seven species of amebae infect humans, differentiated by structure and size.
- Pathogenic species include Entamoeba histolytica; commensal species consist of E. dispar, E. moshkovskii, E. hartmanni, E. coli, Endolimax nana, and Iodamoeba butschlii.
- Entamoeba polecki primarily infects pigs and monkeys but can cause diarrhea in humans.
Entamoeba histolytica Nomenclature
- Classified under subphylum Sarcodina, superclass Rhizopoda, class Lobosea, order Amoebida, family Entamoebidae, genus Entamoeba.
Morphological Characteristics
- Characterized by a vesicular nucleus with a centrally located karyosome and varying chromatin granules.
- Morphological similarities exist between E. histolytica, E. dispar, and E. moshkovskii, requiring careful identification.
Biology of Entamoeba histolytica
- A non-flagellated, pseudopod-forming protozoan; the most invasive Entamoeba, capable of causing colitis and liver abscess.
- Life cycle includes two stages: an infective cyst and an invasive trophozoite.
- Quadrinucleate cysts are resistant to gastric acidity, can survive in moist environments for weeks.
Transmission
- Transmitted through ingestion of cysts from fecally-contaminated materials.
- Alternative routes include venereal transmission via fecal-oral contact and direct inoculation from contaminated enema equipment.
Life Cycle
- Excystation occurs in the intestines, resulting in the transformation of cysts into eight trophozoites through nuclear and cytoplasmic division.
Trophozoite Features
- Trophozoites are motile, averaging 20 μm in size and exhibiting characteristic progressive pseudopod movement in stool specimens.
- Trophozoites can ingest red blood cells, visible as refractile bodies in the amebae's cytoplasm.
- Reproduction occurs through binary fission, followed by encystation to form uninucleate cysts, leading to quadrinucleate cysts through successive nuclear divisions.
Cyst Characteristics
- Cysts typically spherical, ranging from 10 to 20 μm in size.
- Characterized by a highly refractile cyst wall, one to four nuclei, and cigar-shaped chromatoidal bars.
- Cysts are not found within invaded gastrointestinal tissues, unlike trophozoites.
Unique Biochemical Traits
- E. histolytica lacks organelles such as mitochondria and has no rough endoplasmic reticulum or Golgi apparatus.
- Distinct biochemical pathways include the absence of glutathione metabolism and specific protein processing mechanisms, suggesting unique evolutionary adaptations.
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Description
This quiz focuses on protozoan infections, particularly intestinal amebae affecting humans. It covers both pathogenic species like Entamoeba histolytica and non-pathogenic commensals. Test your understanding of their characteristics, differences, and implications in medical parasitology.
