A novel method for detection of viable Giardia cysts in water samples

Assessment of Giardia viability is a major requirement for public health pu rveyors and the water industry. Several indicators of viability such as sta ins, excystation and animal infectivity have been used to enumerate cysts w ith varying degrees of success. A combined detection-viability method for u se in water samples would be useful for detecting and determining the viabi lity of cysts in raw and drinking waters and the efficacy of disinfection a t treatment plants. Distilled water samples were seeded with purified Giard ia cysts and incubated with fluorescein diacetate (FDA) initially to stain viable cysts followed by tetramethyl red labelled anti-Giardia monoclonal a ntibodies (TMR) for confirmation of identity. As a result of FDA staining, green fluorescence of intact viable cysts was observed microscopically usin g a 450-490 nm exciter filter while nonviable cysts were not stained. Giard ia cysts reacted positively with TMR and glowed red using a triple band mic roscope filter with excitations of 400/450/570 nm. Al this wavelength a com bination of FDA and TMR stained viable cysts green internally with a red wa ll while nonviable cysts only stained red. This simple, reliable and quick method allowed differentiation of Giardia cysts in water samples while simu ltaneously determining their viability. (C) 2000 Elsevier Science Ltd. All rights reserved.