Entamoeba histolytica
Introduction:
- Subphylum: Sarcomastigophora
- Class: Rhizopodea
- Subclass: Lobosia
- Order: Amoebida
- Supergroup Amoebozoa
Three distinct morphological forms:
Trophozoite or Vegetative or Amoeboid form
- Resides in the mucosa and sub-mucosa layers of the large intestine.
- Growing or feeding stage
- Cytoplasm divisible into:
- clear, transparent ectoplasm
- inner granular endoplasm.
- The endoplasm contains nucleus, ingested red blood cells, and tissue debris.
- Nuclear membrane is lined with a single layer of uniformly distributed fine chromatin granules
- Karyosome is central in position (not eccentric).
Pre-cystic stage
- Encystment occur in intestinal lumen only
- Contain no RBC and other ingested food particles.
Cystic stage
- Mature Quadrinucleate cyst: Infectious stage
- Present only in the lumen of colon and in mushy or formed feces.
- Its cytoplasm is clear and hyaline
- Nuclear structure retains the characteristics of the trophozoite
When stained with iodine:
- Nuclear chromatin and karyosome appears bright yellow
- Chromidial bars are unstained.
Life Cycle
Faeces of convalescent and carriers
↓
Infective form is mature cyst passed
↓
Cyst ingested through contaminated food
↓
Resist gastric acidity due to presence of cyst wall
↓.
Trypsine lyse the cyst wall in small intestine
↓
Quadrinucleate amoeba comes out.-metacyst.
↓
Nuclei of metacyst immediately undergo division
↓
Form eight nuclei which gets mature to form 8 small amoebae
↓
From small intestine trophozoite are carried to caecum
↓
Lodge in the glandularcrypts
↓
Undergo reproduction by binary fission
↓
Some develop into precystic form and cysts
↓
Which are then passed in feces to repeat the cycle.
Virulence factors
- Cystine Proteinase
- Amoebic Lectin
- lonophore Proteins
- N-acetylglucosamine is the host receptor for Entamoeba histolytica.
- These strains vary according to their isoenzyme patterns (zymodemes).
- E. histolytica strains have 22 zymodeme
- 10 zymodemes are invasive
- 12 are noninvasive.
- Zymodemes of identified according to the electrophoretic mobility of 4 enzymes.
- L-malate : NADP+ Oxidoreductase
- Phosphoglucomutase (PGM)→ most important
- Glucose-phosphate isomerase
- Hexokinase
Cultures media used for cultivation of E.histolytica are: –
- Boeck and Drbohlav’s medium
- Jones medium
- Philip’s medium
- Balamuth’s medium
- Shaffer and Frye’s medium
- Diamond’s medium
- N-acetylglucosamine is the host receptor for Entamoeba histolytica
- Entamoeba histolytica belongs to supergroup Amoebozoa
- Mature cyst of Entamoeba histolytica has 4 vesicular nuclei.
- Nuclear structure retains characteristics of trophozoite in mature cyst
- Trophozoites
- Colonise in the colon
- The presence of red blood cells in the cytoplasm (erythrophagocytosis) is diagnostic of E. histolytical as it is the only intestinal amoeba to exhibit this characteristic.
- The nuclear membrane is lined with a single layer of uniformly distributed fine chromatin granules.
- Karyosome is central in position (not eccentric).
- The pathogenicity of Entamoeba histolytica is indicated by isoenzymes pattern
Cultures media used for cultivation of E.histolytica are: –
- Boeck and Drbohlav’s medium
- Jones medium
- Philip’s medium
- Balamuth’s medium
- Shaffer and Frye’s medium
- Diamond’s medium
