AMEBAS

• Amebas

  Unicellular organisms and the lowest form of animal life
• Phyla of medical interest in humans (Protozoa subkingdom)

  • Sarcomastigophora, subphylum Sarcodina (includes pathogenic and nonpathogenic amebas)
  • Other phyla not specified
• Amebas


  • They move by extending their cytoplasm in the form of pseudopods (false feet)
  • They have two morphological forms: trophozoites (feeding, multiplying form with pseudopods) and cysts (non-feeding stage with thick protective cell wall)
• Amebic life cycle

  1. Ingestion of infective cyst

  2. Excystation (cyst to trophozoite) in ileocecal area

  3. Trophozoite replication by asexual binary fission

  4. Encystation (trophozoite to cyst) in intestine when environment becomes unacceptable
• Trophozoites are easily destroyed by gastric juices and environment outside host, so not usually transmitted
• Cysts can enter outside environment with feces and remain viable for long periods
• Basic life cycle is the same for all intestinal amebas
• Trophozoites


  Feeding, multiplying form with pseudopods
• Cysts


  Non-feeding stage with thick protective cell wall
• Amebic trophozoites and cysts may be seen in stool samples
• Trophozoites are more likely recovered from loose stools, cysts from formed stools
• Permanent stained smears are required to accurately identify amebas
• Only Entamoeba histolytica is considered a pathogenic intestinal ameba
• Intestinal ameba infections are most common in underdeveloped countries with poor sanitary conditions
• Intestinal ameba species

  • Entamoeba histolytica
  • Entamoeba hartmanni
  • Entamoeba coli
  • Entamoeba polecki
  • Endolimax nana
  • Iodamoeba bütschlii
• Extraintestinal ameba species

  • Entamoeba gingivalis
  • Naegleria fowleri
  • Acanthamoeba species
• Entamoeba histolytica

  Pathogenic intestinal ameba that can cause intestinal and extraintestinal amebiasis
• Entamoeba histolytica trophozoites

  • Size range 8-65 μm, average 12-25 μm
  • Rapid, unidirectional, progressive movement with finger-like hyaline pseudopods
  • Single nucleus with small central karyosome and even peripheral chromatin
  • Finely granular cytoplasm, may contain ingested red blood cells
• Entamoeba histolytica cysts

  • Size range 8-22 μm, average 12-18 μm
  • Spherical to round shape
  • 1-4 nuclei with small central karyosome and even peripheral chromatin
  • Chromatoid bars and diffuse glycogen mass in young cysts
• Cytoplasm


  The jelly-like substance inside a cell that contains the organelles
• Entamoeba histolytica trophozoite

  • Central karyosome
  • Even peripheral chromatin
  • Pseudopod
  • Size range: 5-15 μm
• Cyst


  The infective stage of Entamoeba histolytica
• Entamoeba hartmanni trophozoite

  Size accounts for the major difference between the trophozoites and cysts of Entamoeba hartmanni and Entamoeba histolytica
• Entamoeba dispar is a nonpathogenic ameba that is morphologically identical to Entamoeba histolytica
• It is often impossible to distinguish Entamoeba histolytica and Entamoeba dispar based on morphology alone
• If trophozoites containing ingested red blood cells are seen, it is appropriate to report them as Entamoeba histolytica
• In cases where identification is not apparent, speciation requires specialized testing methodologies that include DNA probes and electrophoresis techniques designed to target enzymes
• Average size of Entamoeba hartmanni trophozoite

  1. 12 μm
• Entamoeba hartmanni


  Intestinal amebiasis, amebic colitis, amebic dysentery, extraintestinal amebiasis
• Entamoeba hartmanni trophozoite

  • Size range: 5-15 μm
  • Motility: Nonprogressive, finger-like pseudopods
  • Number of nuclei: One
  • Karyosome: Small and central
  • Peripheral chromatin: Fine and evenly distributed
  • Cytoplasm: Finely granular, may contain ingested bacteria
  • Cytoplasmic inclusions: No ingested red blood cells
• Entamoeba hartmanni cyst

  • Size range: 5-12 μm
  • Shape: Spherical
  • Number of nuclei: One to four
  • Karyosome: Small and central
  • Peripheral chromatin: Fine and evenly distributed
  • Cytoplasm: Finely granular, contains diffuse glycogen mass and rounded-end chromatoid bars in young cysts
• Laboratory diagnosis of Entamoeba hartmanni is accomplished by examining stool for trophozoites and cysts
• The size ranges of Entamoeba histolytica and Entamoeba hartmanni overlap, making specific identification based only on size impossible in some cases
• The geographic distribution of Entamoeba hartmanni is cosmopolitan
• Infections with Entamoeba hartmanni are typically asymptomatic
• Entamoeba hartmanni is generally considered a nonpathogen and treatment is usually not indicated
• Good sanitation and personal hygiene practices, as well as protection of food from flies and cockroaches, will help prevent the spread of Entamoeba hartmanni
• Entamoeba coli trophozoite

  Size range: 12-55 μm<|>Motility: Nonprogressive, blunt pseudopods<|>Number of nuclei: One<|>Karyosome: Large, irregular shape, eccentric<|>Peripheral chromatin: Unevenly distributed<|>Cytoplasm: Coarse and granulated, contains vacuoles with ingested bacteria<|>Cytoplasmic inclusions: No ingested red blood cells
• Entamoeba coli cyst

  • Size range: 8-35 μm
  • Shape: Round to spherical
  • Number of nuclei: One to eight
  • Karyosome: Large, irregular shape, eccentric
  • Peripheral chromatin: Unevenly distributed
  • Cytoplasm: Coarse and granulated, contains diffuse glycogen mass in young cysts, may displace nuclei
  • Cytoplasmic inclusions: Thin chromatoid bars with pointed to splintered ends in young cysts
• Stool examination is the method of choice for the recovery of Entamoeba coli trophozoites and cysts