Blastocystis hominis ultrastructure and encystment in polixenicculture.
2007
Blastocystis hominis (Bh) is an organism, whose taxonomy, biological
cycle and mode of transmission is controversial. A variety of forms
have been described using ligth and transmission electron microscopy
(TEM) and there is not uniformity in reporting cysts characteristics in
TEM. The knowledge of the morphology of Blastocystis hominis is
indispensable for identification and biological studies. Morphologic
characterization was made in B. hominis, isolated Bh69:UCV, obtained
from the original culture from a patient's faeces with intestinal
symptomatology and maintained in the Amibiasis laboratory in polixenic
culture in Boeck-Drbohlav (modified) media (BDM). The vegetative forms
of the parasite, central body form (CBF), granular form (GF), amoeboid
form (AF), and cysts which spontaneously appeared on the cultures, are
described, using light microscope (400x and 1000x) and TEM, according
to conventional techniques. All the vegetative forms are
characteristically surrounded by a mucoid cover, and have a central
body that occupies most of cell and delimits a thin cytoplasmic ring,
in which the cellular organelles are observed like refractile
inclusions. There are two types of cysts, naked cyst are spherical to
ovoid, refractile, 5-6 μm of diameter and cyst with external
cover, separated by a space of 2-3 μm. By TEM, in the cytoplasm of
all the forms, a nucleus with chromatin in crescent-shaped form,
spherical mitochondria with few crests, digestive vacuoles, Golgi, RER
and great amount of ribosomes and glicocalix on the plasmatic
membrane were observed. Cyst wall showed three defined zones, with the
external cover made of fibrogranular and vesicular material. Some cysts
presented spherical structures whose morphology does not correspond
with mitochondrias or nuclei and they could be daughters cells. The
morphologic characteristics agree with previously reported for the
vegetative forms and cysts, and we suggest a possible sequence in
vegetative forms transformation to resistance forms
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