Amoeboid Protozoa

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tropical diseases

Text of Amoeboid Protozoa

BY2012 Microbiology Gallery of Amoeboid Protozoa

Amoeboid Protozoa Unicellular protozoa move and feed by means of cytoplasmic projections termed pseudopodia Amoeboid protozoa are characterised on the form and structure of their pseudopods Common in soils and aquatic habitats Entamoeba are both pathogens of and commensals in animals Dictyostelium (a slime mould) is a amoeba with a complex life cycle involving unicellular and multicellular phases

Amoeba proteusPseudopodium

Granular cytoplasm

Contractile vacuole


Food vacuole


Diagrammatic drawing of an amoeba

Amoeba proteus

Diagrammatic drawing of an amoeba

Amoeba proteusFood vacuoles Nucleus


Contractile vacuole

Nomarski differential interference microcopy

Amoeba proteus


Phase-contrast microscopy of an amoeba cell

Amoeba0.1 mm

Food vacuoles Contractile vacuole

Nucleus Phase-contrast microscopy of a living amoeba cell

Amoeba proteusNucleus

Pseudopodia Contractile vacuole Food vacuoles

Nomarski differential interference microscopy

Amoeba proteusPseudopodia Nucleus

Contractile vacuole

Phase-contrast microscopy of a living amoeba cell

Freshwater amoebae

Phase-contrast microscopy of amoebae

Freshwater amoeba

Phase-contrast microscopy of an amoeba

Freshwater amoeba

Phase-contrast microscopy of an amoeba


Excellent video of amoeba moving (WMV format):

Amoeba proteus

Time-lapse photographs of amoebic motility by pseudopod extension

Pfiesteria shumwayae Freshwater amoeba

Pfiesteria shumwayae amoebae engulfing a crytomonad (arrowed) [small freshwater flagellate protozoa] (A) and showing two engulfed cryptomonads (B)

Metachaos gratum Freshwater amoeba

Nomarski differential interference microcopy

Amoeba proteusFood vacuole Pseudopodium

Pseudopodium Nucleus Stained Amoeba proteus

Amoeba proteusPseudopodia


Food vacuole

Stained Amoeba proteus

Amoeba proteusC

Stained Amoeba proteus: A, nucleus; B, Pseudopodia; C, Food vacuole

Entamoeba histolytica Life Cycle

Entamoeba histolytica Life Cyclea Cyst

g Excretion in faeces

b Ingestion by human of contaminated food or water

f Encystment in colon

c Excystation in small intestine

d Trophozoite e h (invasive) Amoebic colitis (amoebic) Liver abscess


Asymptomatic colonisation

Entamoeba histolytica TrophozoitesIngested red blood cells Nucleus

Ingested red blood cells Nucleus

Following ingestion of cysts in faecally contaminated water or food, excystation occurs in the small intestine with the emergence amoeboid trophozoites which migrate to the large intestine

Entamoeba histolytica Trophozoites


Stained Entamoeba histolytica trophozoite with ingested red blood cells (black arrows)

Entamoeba histolytica Trophozoites

Anders Magnusson

Trophozoites with intracellular and extracellular red blood cells

Entamoeba histolytica - Cysts

Mature cystcb = Chromatid bodies


Amoeboid trophozoites undergo encystment in the colon due to dehydration of faeces immature cysts have two nuclei, mature cysts have four nuclei

Entamoeba histolytica Encystment

1 Nucleus

2 Nuclei

4 Nuclei

Entamoeba - Cysts

Nuclei of cysts are arrowed

Entamoeba histolytica Mature Cysts

Nuclei are arrowed

Entamoeba dispar A non-pathogenic Entamoeba



Cyst with 4 nuclei

Entamoeba coli A non-pathogenic EntamoebaNucleus


Cyst has 8 nuclei

Life Cycle of Slime Mould Amoeba Dictyostelium

Life Cycle of Slime Mould Amoeba Dictyostelium

Single amoeboid cell

Amoebae swarm together

Slug of amoeboid cells

Dictyostelium discoides is an amoeba that lives in soil and moist leaf litter and belongs to the group termed slime moulds. Dictyostelium spores released from a mature fruiting body germinate forming amoebae. The amoebae feed on bacteria and reproduce by mitosis. When food runs out, the amoebae aggregrate forming a muticellular slug. The starvation stress induces expression of cell-cell adhesion glycoproteins on their surfaces, causing the amoebae to stick together.

Life Cycle of Slime Mould Amoeba DictyosteliumSorus Fruiting Body Stalk

Basal disk Amoebae within the Dictyostelium slug differentiate, some forming the stalk of the fruiting body while others differentiate at the head of the stalk (sorus) into spores. The fruiting body comprises 50-80,000 cells.