AMOEBAE

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AMOEBAE
M.PRASAD NAIDUMSc, (Medical) Ph.D. (Medical)
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• An amoeba (also ameba, amœba or amoeboid) is a
  type of cell or organism which has the ability to
  alter its shape, primarily by extending and
  retracting pseudopods. Amoebae do not form a
  single taxonomic group, but are found in every
  major lineage of eukaryotic organisms (domain
  Eukaryota).

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• Amoeoboid cells occur not only among
  the protozoa, but also fungi, algae and animals.
• Among microbiologists, the terms "amoeboid" and
  "amoebae" are often used interchangeably for any
  organism that exhibits amoeboid movement.

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• The best known amoeboid protists are the "giant
  amoebae" Chaos carolinense and Amoeba proteus,
  both of which are widely cultivated and studied
  in classrooms and laboratories. Other well known
  species include the so-called "brain-eating
  amoeba" Naegleria fowleri, the intestinal
  parasiteEntamoeba histolytica, which
  causes amoebic dysentery, and the multicellular
  "social amoeba" Dictyostelium discoideum.

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Naegleria fowleri

• Primary Amoebic Meningo Encephalitis
• (PAM)
• Fowler Carter (1965 ).

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Amebiasis Caused by Entamoeba histolytica. (a)
Light micrographs of a trophozoite (1,000)
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A cyst (1,000).
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• TROPHOZOITE
• Vegetative Feeding stage .
• CSF Tissue .
• 10 -20 µm , Karyosome with halo .
• Actively motile (Lobopodia )
• Binary fission .

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• Amoebae move and eat by using pseudopods, which
  are bulges of cytoplasm formed by the coordinated
  action of actin microfilaments pushing out
  the plasma membrane that surrounds the cell.
• Groups of amoebae are distinguished by the
  appearance and internal structure of their
  pseudopods. 
• Amoebozoan species typically have bulbous
  pseudopods, rounded at the ends and roughly
  tubular in cross-section (lobose)

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• Cercozoan amoeboids, such as Euglypha and Gromia,
  have slender, thread-like (filose)
  pseudopods. Foraminiferan emit fine, branching
  pseudopods that merge with one another to form
  net-like (reticulose) structures. Some groups,
  such as the Radiolaria and the amoeboids loosely
  called Heliozoa, have stiff, needle-like,
  radiating actinopods supported from within by
  bundles of microtubules

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SHAPE, MOVEMENT AND NUTRITION
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• Free-living amoebae may be "testate" (enclosed
  within a hard shell), or "naked" (lacking any
  hard covering). Testate amoebae shells are
  composed various substances, including calcium, si
  lica, chitin, or agglutinations of found
  materials like small grains of sand and
  the frustules of diatoms.
• To regulate osmotic pressure, most freshwater
  amoebae have a contractile vacuole which expels
  excess water from the cell.

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•  This organelle is necessary because freshwater
  has a lower concentration of solutes (such as
  salt) than the amoeba's own internal fluids
  (cytosol). Because the surrounding water
  is hypotonic with respect to the contents of the
  cell, water is transferred across the amoeba's
  cell membrane by osmosis. Without a contractile
  vacuole, the cell would fill with excess water
  and, eventually, burst. Marine amoebae do not
  usually possess a contractile vacuole, because
  the concentration of solutes within the cell are
  in balance with the tonicity of the surrounding
  water.
• The food sources of amoebae vary. Some amoebae
  are predatory and live by consuming bacteria and
  other protists.

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• Some are detritivores and eat dead organic
  material. Amoebae typically ingest their food
  by phagocytosis, extending pseudopods to encircle
  and engulf live prey or particles of scavenged
  material.
• Amoeboid cells do not have a mouth or cytostome,
  and there is no fixed place on the cell at which
  phagocytosis normally occurs. Some amoebae also
  feed by pinocytosis, imbibing dissolved nutrients
  through vesicles formed within the cell membrane.

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AMOEBAE IN MULTICELLULAR ORGANISMS ANIMALS AND
SLIME MOLDS
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• Amoebae in multicellular organisms animals and
  slime molds
• Some multicellular organisms have amoeboid cells
  only in certain phases of life, or use amoeboid
  movements for specialized functions.
• In the immune system of humans and other
  animals, amoeboid white blood cells pursue
  invading organisms, such as bacteria and
  pathogenic protists, and engulf them
  by phagocytosis.

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• Amoeboid stages also occur in the multicellular fu
  ngus-like protists, the so-called slime molds.
• Both the plasmodial slime molds, currently
  classified in the class Myxogastria, and the
  cellular slime molds of the groups Acrasida and Di
  ctyosteliida, live as amoebae during their
  feeding stage.

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• The cells of the former form a giant multinucleate
   amoeboid organism,while the cells of the latter
  live separately until food runs out, at which
  time the amoebae aggregate to form a
  multicellular migrating slug which functions as a
  single organism

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LIFE CYCLE

• ONE HOST Man .
• Asexual Generation cycle .
• MOI Swimming in Contaminated water .
• Infective form Trophozoites .
• Cysts (Inhalation ) Rare .

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• Entry Nose
• Olfactory mucosa.
• ?
• Olfactory bulbs
• ?
• Sub Arachnoid space.
• ?
• (Multiplication)
• ?
• Choroid plexus
• ?
• Ventricular destruction.
• ?
• Ependymitis.

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• Trophozoites Cysts (unfavorable
  conditions ) .
• PATHOGENESIS
• IP 2 -15 days .(5 days )
• Neurotropic .
• Brain tissue destruction .
• Acute Hemorrhagic Necrotising meningo
  encephalitis .
• Cysts are absent in humans .

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• CLINICAL FEATURES
• Children Young adults .
• PAM .
• Rapid onset Fulminant .

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• Sudden severe Persistent Bifrontal /Bitemporal
  
• Headache ,Nausea , Projectile vomiting .
• Ageusia (loss of taste function).
• Parosmia (olfactory dysfunction).
• Generalized seizures
• Photophobia
• Coma
• Death
• Poor Prognosis .(95 death )

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DIAGNOSIS

• Specimen CSF (Antemortem )
• Brain Biopsy (Post mortem ).
• CSF
• Wet mount Plenty of Actively motile
  trophozoites .
• Phase Contrast Microscopy .

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• Stains Trichrome , Giemsa , Wright .
• Direct Fluorescent Antibody
  staining .
• BIOPSY IF Immuno Peroxidase method .

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• Serodiagnosis Not Useful .
• Molecular methods DNA probes PCR .
• CSF Features of Pyogenic
  Meningitis .

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• Treatment Amphotericin B Rifampicin,Micon
  azole .
• Prevention

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Acanthamoeba

• Opportunistic pathogens .
• 1. A.castellani .
• 2. A.astronyxis .
• 3. A.polyphaga .
• 4. A.culbertsoni .

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• HABITAT Dust , Soil , Sand , Rivers ,
  Ponds , Tap water .
• MORPHOLOGY
• 2 stages .
• Trophozoite .
• Cyst .

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• TROPHOZOITE
• Variable size shape .
• 10 -40 µm .
• Acanthopodia Characteristic feature .

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• CYST
• Polygonal /Spherical /Star shaped .
• 15 -20 µm.
• Double layered cyst wall .

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• LIFE CYCLE
• MOI Invasion of Broken skin .
• Inhalation of Cysts Trophozoites .
• ROUTE Lungs to Blood stream (Multiplicatio
  n )
• CNS .
• Sites of Localisation Basal ganglia ,
• Posterior fossa , Cerebellum .

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• PATHOGENESIS
• Lesions of Brain , Eye , Lungs Skin .
• Brain Patchy , Sub Acute lesions of
  granulomatous encephalitis .
• Skin Nodular Ulcerative lesion. Abscess .
• Cornea Epithelial inflammation, Hypopyon .

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• CLINICAL MANIFESTATIONS
• Granulomatous Amoebic Encephalitis (GAM)
• Acanthamoeba Keratitis .
• Cutaneous Lesions .

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• GAE
• Rare .
• Risk factors
• AIDS ,
• Immunosupression,Organ transplantation
• Malnourished .

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• Clinical features
• Low grade fever,stiff neck ,
• Altered Mental status .
• Seizures ,
• Cranial palsies ,
• Hemiparesis , Ataxia ,
• Photophobia
• Coma ,
• Multi organ Failure ,
• Death .

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• Acanthamoeba Keratitis
• Contact lens wearers .(trauma )
• Chronic , Progressive , Ulceration .
• Annular Infiltration Congested Cornea .
• Perforation .
• Blindness .

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• CUTANEOUS LESIONS
• Face Extremities .
• Nodules , papules ulcers .
• Poor Prognosis .
• GAE Fatal .

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• DIAGNOSIS
• Microscopy
• Trophozoites Cysts In Brain Biopsy Corneal
  Smears .
• Wet mount Trophozoites Cysts .

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• Stains Acridine orange , Giemsa , LCB .
• IF .
• Culture
• Serlogical tests Not useful .
• Molecular methods .
• Imaging Methods .

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• TREATMENT
• GAE No therapy. Sulphonamides ,
  Cotrimoxazole ,
• Polymyxin B .
• Keratitis Topical Miconazole .
• Kertoplasty .
• PROPHYLAXIS
• Disinfecting Contact lenses .

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Foraminiferan (Ammonia tepida)
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Shell of the testate amoeba Difflugia acuminata,
made up of mineral particles
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