A simple method for excystation of Giardia lamblia cysts

Fresh Giardia lamblia trophozoites were isolated by in vitro excystation of purified cysts from the faeces of Saudi patients. The method consisted of mixing one part of the cyst suspension with nine parts of 1 N hydrochloric acid, at pH 2, then culturing the excysted trophozoites in modified TYI-S-33 medium in sealed glass vials. During the excystation process most cysts developed a space between the trophozoite and the cyst wall, and after several steps of enlargement the trophozoite emerged at the posterior end of the cyst. Keeping the cysts at 4 degrees C for more than 10 days did not affect the excystation process. Trophozoites obtained by this method can be cryopreserved and recultured without significant loss of activity. This is a simple and rapid method of obtaining G. lamblia trophozoites from cysts in stools or from other sources.