Entamoeba histolytica

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.
Pathogenicity
  • 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.
  1. L-malate : NADP+ Oxidoreductase
  2. Phosphoglucomutase (PGM)→ most important
  3. Glucose-phosphate isomerase
  4. 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
Exam Question
 
  • 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
Don’t Forget to Solve all the previous Year Question asked on Entamoeba histolytica

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