the inhibitory properties of and mode of action of plant essential oils ...

Figure 1.3 Trophozoites of Giardia duodenalis.
Live trophozoites were isolated in vitro from axenic cultures and viewed under
brightfield microscopy (x1000 mag) in ventral view (C) and dorsal view (A) and
ventrally under scanning electron microscopy (B). The parasites show classical
pyriform morphology and the flagella can be clearly seen in all panels (fl) with the
dual nuclei visible in dorsal view (Panel A; nu). The ventral disc is also visible in
panel C (sd) and in panel B with the ventral flagella easily visible. SEM image
courtesy of the Centres for Disease Control and Prevention (CDC) and Dr. J. Carr.
Brightfield microscopy images by J-P Anthony (copyright © SPDL).
Cyst morphology
The cyst is produced in the lower bowel and cysts occur in large numbers in the
stool. They are oval, measuring approximately 5 by 7 to 10 µm in diameter.
Encystation occurs after the trophozoite has undergone nuclear division but before
cytokinesis, thus providing the cyst with a single trophozoite containing 4 nuclei
(Figure 1.4) and capable of rapidly completing cytoplasmic division upon
excystation, producing 2 trophozoites faster than with a normal replication cycle.
A web-like filamentous layer comprises the outer cyst wall with each filament being
7 – 20 nm in diameter (Erlandsen et al. 1990; Erlandsen, Bemrick and Pawley 1989)
and comprising of four major proteins, 29, 75, 88 and 102 kDa in size (Erlandsen et
al. 1990) 2 of them being known as cyst wall proteins (CWP) 1 and 2. Underlying
this filamentous outer cyst wall is a double membranous layer, the inner membrane
layer being separated from the outer membrane by a thin layer of cytoplasm and
these membranes separated from the trophozoite plasma membrane by a peritrophic
space. It is currently thought that this peritrophic space originates from the
20