Characterization of the nature of oxidant action using morphological changes observed following exposure of Giardia lamblia to ozone and chlorine

Morphology of Giardia lamblia cysts following single or sequential treatment with ozone and free chlorine was studied. Experiments were conducted in oxidant demand-free phosphate buffer using in vitro derived G. lamblia cysts. Nucleic acid staining using LIVE/DEAD BacLight™ was used for the evaluation of cyst viability. Examination of the ultrastructure of cysts was carried out using transmission electron microscopy. Cyst wall damage, plasmalemma breakage, lysis of peripheral vacuoles, nuclear degradation and other internal organelle damages illustrated the cyst death process elicited by oxidants. Inactivation by ozone and by free chlorine differed in the nature their damages to the endomembrane system, the nuclear structure and the cytoplasm. Cysts exposed to multiple chemical oxidants showed damages characteristic of changes elicited by both chemicals. Greater cytoplasmic damages were observed in cysts treated with free chlorine followed by ozone than cysts treated with ozone followed by free chlorine.