A method was developed for the detection of Giardia
cysts by using the polymerase chain reaction (PCR) and the giardin gene as the target.
DNA amplification by PCR, using giardin
DNA as the target, resulted in detection of both live and dead
cysts. When giardin
mRNA was used as the target, the ability to amplify
cDNA by PCR depended on the mode of killing.
Cysts killed by freezing were not detected by PCR when giardin
mRNA was the target.
Cysts killed by heating or exposure to
monochloramine, however, gave positive detection signals for both
DNA and giardin
mRNA targets. The amount of giardin
mRNA and total
RNA was significantly increased in live
cysts following the induction of excystation.
Cysts killed by freezing, heating, or exposure to
monochloramine did not show a change in
RNA content. The detection of the giardin gene by PCR permits a sensitive and specific diagnosis for Giardia spp. Discrimination between live and dead
cysts can be made by measuring the amounts of
RNA or PCR-amplified product from the giardin
mRNA target before and after the induction of excystation.