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A comparison of fluorescein diacetate and propidium iodide staining and in vitro excystation for determining Giardia intestinalis cyst viability

Published online by Cambridge University Press:  06 April 2009

A. L. Smith  and
H. V. Smith
A. L. Smith
Affiliation:
Scottish Parasite Diagnostic Laboratory, Department of Bacteriology, Stobhill General Hospital, Glasgow G21 3UW
H. V. Smith
Affiliation:
Scottish Parasite Diagnostic Laboratory, Department of Bacteriology, Stobhill General Hospital, Glasgow G21 3UW
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Summary

The viability of 4 human isolates of Giardia intestinalis cysts using either the fluorogenic vital dyes fluorescein diacetate (FDA) and propidium iodide (PI) or in vitro excystation was assessed. Whereas viable cysts, as defined by in vitro excystation were present in each of the 4 isolates, cysts from only 3 of the 4 isolates took up the vital dyes. FDA consistently over-estimated cyst viability whilst PI under-estimated non-viable cysts when compared with in vitro excystation. Following in vitro excystation, both FDA and PI stained a proportion of unexcysted cysts indicating that FDA stained cysts which were incapable of excystation, whereas PI did not stain all cysts which were incapable of excystation. One human cyst isolate, which underwent in vitro excystation, could not be stained with either FDA or PI. In the absence of currently more specific fluorescent indicators of viability, PI alone could be used to determine the lower limit of nonviability in positive water-related samples, where small numbers of cysts are to be expected.

Keywords

Giardia intestinaliscyst viabilityexcystationstainingfluorogenic vital dyes.
Type
Research Article
Information
Parasitology , Volume 99 , Issue 3 , December 1989 , pp. 329 - 331
Copyright
Copyright © Cambridge University Press 1989

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