Focus on pathogens: D' fragilis diagnosisID

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Focus on pathogens D. fragilis diagnosis/ID

• Very difficult to distinguish from ameoba
  morphologically - wet preparations of little
  value - requires good quality permanent stain.
• Morphology of troph (D.fragilis has no cyst)
• Size 5-12 micrometers much smaller than E.
  histolytica but very similar to the commensals
• Shape amoeboid with broad hyaline pseudopods
• Motility not much via pseudopods that are
  angular,
• serated, broad-lobed and transparent
• Nucleus one or two (80 have two nuclei), very
  delicate nuclear membranes, difficult to see.
• Cytoplasm vacuolated and often contain
  bacteria
• Karyosome composed of 4-8 fragments

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Drawing top left, Fe hematoxylin bottom left,
trichrome right
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Focus on pathogens Blastocystis hominis

• Facts / life-cycle Classification is
  uncertain(!) and much is not known, including
  much about the odd life-cycle. As opposed of D.
  fragilis, the organism enters and exits host as a
  cyst, probably via direct fecal-oral means.
  Cysts undergo mitosis to become 2 forms 1. a
  multi-vacuolar form which morphs into a
  thin-walled, auto-infecting cyst, and 2. an
  amoeboid form which morphs into the thick walled
  cyst that exits the host in feces. Some sources
  suggest that 6 forms of the organism exist.
• Epidemiology controversial - appears to be a
  frequent resident of the intestinal tract, either
  as normal flora or the most common parasitic
  infection of humans.

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Proposed life-cycle for B. hominis
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Focus on pathogens B. hominis pathology/clinical
symptoms

• Disease gastroenteritis
• Pathology and clinical manifestation
• recurrent diarrhea without fever
• abdominal cramping
• perianal pruritis

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Focus on pathogens B. hominis diagnosis/ID

• Oval-round cyst, 8-10uM with
• 1) a large central homogenous mass (vacuole) that
  stains blue-green with trichrome stain
• 2) 1-4 oval red staining (trichrome) nuclei
  located in a narrow rim of cytoplasm surrounding
  the central mass

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2 on left are Iodine wet mounts Trichrome
stain on right
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Commensal intestinal amoeba

• Significant as look-alikes of pathogens,
  especially of
• E. histolytica.
• Entamoeba dispar Entamoeba coli
  Entamoeba hartmanii Endolimax
  nana Iodamoeba butschlii

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Entamoeba dispar

• Entamoeba dispar is a commensal ameba that cannot
  be differentiated for E. histolytica on
  morphological grounds except that Trophozoites
  never contain RBCs
• E. dispar can be differentiated from E.
  histolytica by using genetic or cytochemical
  analyses. These methods are currently performed
  only in research laboratories.

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Entamoeba coli

• Commensal nonpathogenic ameba
• Diagnostic features of trophs in wet preparations
• Non-directional (random) motility
• Granular blunt pseudopods
• Usually contain ingested bacteria and yeast
• Nuclear details not visible or definitive
  (requires permanent staining)