Entamoeba polecki
This amoeba most likely
has worldwide distribution and can be found as an intestinal parasite in pigs
and monkeys. It is generally considered
to be non-pathogenic for humans but has occasionally been recovered from patients
with loose stools and intestinal discomfort.
Several sources have stated that in Papua New Guinea, E.polecki has been recovered as the most
common intestinal parasite from the inhabitants. Living closely with these animals my increase
the chances of carrying the parasite. E.polecki makes its home in the large
intestine of man.
Trophozoites:
E.polecki
trophs have an average size of 12 µm to 18 µm but can range from 10 µm to as
large as 25 µm. Its cytoplasm can be
vacuolated and may contain ingested bacteria and yeast. The size and cytoplasmic appearance may cause
it to be confused with Entamoeba coli.
The karyosome may not be visible which has the nucleus appear
empty. When present, the karyosome is
usually minute and centrally located, or nearly so. It however may occasionally appear diffuse. Peripheral chromatin can vary from being fine
and evenly distributed as in E.histolytica,
or coarse and irregularly distributed as in E.coli. This variability may make diagnosis a
challenge.
Cysts:
E.polecki
cysts are about 9 µm to 15 µm but can be as large as 24 µm and usually contain
only one nucleus (usually E.histolytica
has 4, E.coli has 8). It has rarely been reported as being
binucleate. The karyosome again can be
minute can compact or it may be larger and diffuse – it may be centrally
located within the nucleus or somewhat eccentric. Peripheral chromatin may be delicate to
coarse but is evenly distributed on the nuclear membrane. Chromatoidal material is usually abundant but
highly variable in shape and size. It
may be present as larger rods with rounded or splintered ends and they may be
arranged parallel to each other in the cyst.
Unique to these cysts may be an inclusion body of variable size. It stains a monochromatic grayish-purple with
Iron hematoxylin stain or greenish with the trichrome stain. In an iodine stained preparation it usually
appears light brown in contrast to the intensely dark brown staining of
glycogen vacuoles. The nature of these
inclusions is not known but does not appear to be glycogen.
Differentiation:
Differentiating the E.polecki trophozoites from E.histolytica and E.coli may be difficult as the size ranges overlap and both the
cytoplasmic and nuclear appearance can mimic both. If examining a specimen that has amoeba
showing characteristic of both E.histolytica
& E.coli, the presence of E.polecki should be considered.
Chromatoid bodies are usually are more numerous and show greater pleomorphism
in E.polecki than E.histolytica. E.polecki cytoplasm often stains very darkly
making it difficult to see the nucleus, inclusion mass and chromatoid bodies in
the same plane of focus
Note: The
photographs which follow were of E.polecki
found in a fecal specimen obtained from a patient with gastrointestinal
discomfort. Only trophozoites were
present in the sample. I’m rather
unhappy with the quality of the photos I took and present here. The features lack resolution and the amoeba
appears darker in the photos than they did when viewed through the light
microscope. The features appear to be
over saturated in colour and “bleed” together, obscuring details. I was unable to correct for this satisfactorily
with photo software post exposure. This
specimen also contained Entamobea hartmanni trophs. Identification was confirmed by our provincial
public health laboratory. Here they are for what they’re worth.
All photos below were taken using the Nikon 'Coolpix' camera at 1000X magnification and are from an Iron-Hematoxylin stained preparation.
E.polecki trophozoite exhibiting a coarse cytoplasm. Peripheral chromatin in the nucleus is rather evenly distributed. Karyosome is central but not distinct.
E.polecki trophozoite showing rather evenly distributed peripheral chromatin in the nucleus and as above the karyosome is rather diffuse and slightly eccentric.
E.polecki trophozoite showing a rather coarse cytoplasm with ingested material (bacteria). The karyosome shows even, dense peripheral chromatin but the karyosome appears to be absent in all planes of focus. Above the E.hartmanni troph may be a somewhat distorted Blastocystis hominis.
E.polecki troph as above. "Dirty" cytoplasm, even dense peripheral chromatin in the nucleus with a somewhat diffuse karyosome, slightly eccentric.
This specimen contained both E.polecki trophs and E.hartmanni trophs. Note the size difference.
E.hartmanni troph and a second cell with too little detail to identify confidently.
E.policki troph (inset left) to demonstrate the size difference between it and the E.hartmanni troph.
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