in vitro culture and isoenzyme analysis of giardia lamblia

Chapter 3
IN VITRO EXCYSTMENT
3.1 INTRODUCTION
Research on excystation of Giardia began as early as 1925 (Hegner, 1925). In his
later report on in vitro excystation of human intestinal protozoa, he recognised
moisture and a temperature of about 37°C as the only factors necessary for
excystation (Hegner, 1927). It was only in 1979 that all conditions responsible for
induction of this process were defined by Bingham and Meyer (1979). These
authors demonstrated that Giardia excystation is pH dependant, being initiated by
acidic conditions. The process is only completed successfully if the acid exposure
is promptly followed by incubation in an alkaline medium. This process was
described as analogous to passage of cysts through an acidic stomach followed
by the alkaline environment encountered in the duodenum. They illustrated that
the hydrogeh ion was responsiQle for induction of excystation. In this experiment,
cysts were successfully excysted after being exposed to synthetic gastric juice
containing inorganic salts and pepsin at acid pH.
Most excystation methods subsequently published have been based on these
workers' findings, some with slight modifications. Various combinations of salts,
bicarbonate and pepsin or trypsin were mainly used in the modified versions
(Bingham et al., 1979; Rice & Schaeffer, 1981; Coggins & Schaefer, 1986; Buchel
et al., 1987; Hamilton & Jackson, 1990). In recent years, several workers have
reported successful excystation of Giardia from humans and subsequent
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