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Appl. Environ. Microbiol., 02 1995, 690-697, Vol 61, No. 2
MW LeChevallier, WD Norton, JE Siegel and M Abbaszadegan
The accurate determination of the presence of Giardia cysts and
Cryptosporidium oocysts in surface waters requires a reliable method for
the detection and enumeration of these pathogenic organisms. Published
methods have usually reported recovery efficiencies of less than 50% for
both cysts and oocysts. Typically, the losses are greater for
Cryptosporidium oocysts than they are for Giardia cysts. The purpose of
this study was to examine procedures used for sample collection, elution,
concentration, and clarification to determine when losses of cysts and
oocysts occurred during processing. The results showed that major losses of
cysts and oocysts occurred during centrifugation and clarification.
Depending on the centrifugation force, oocyst losses of as high as 30%
occurred for each centrifugation step. A 1.15-specific-gravity
Percoll-sucrose gradient was needed to optimize recovery of oocysts from
natural water samples. Minor improvements in the procedure could be
accomplished by selecting a filter other than the recommended
1-micron-pore-size (nominal-porosity) polypropylene filter.
Copyright © 1995, American Society for Microbiology
Evaluation of the immunofluorescence procedure for detection of Giardia cysts and Cryptosporidium oocysts in water
American Water Works Service Company, Inc., Voorhees, New Jersey 08043, USA.
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