Analysis-only Detection of Giardia by Combining Immunomagnetic Separation and Two-Color Flow Cytometry

Belinda C. Ferrari*, Duncan Veal

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


Background: Giardia is a protozoan parasite of concern to water utilities. Giardia detection relies on cyst isolation and confirmation with the use of fluorescence microscopy. It is of interest to develop a flow cytometric (FCM) method that reliably detects one cyst in 10 L of water. To date all available antibodies have targeted the same epitope on the cyst wall. To achieve a reliable method, two independent probes are required. Methods: Giardia cysts were spiked into a backwash water sample with and without prior hybridization to peptide nucleic acid (PNA) probes. Immunomagnetic separation (IMS) as a pre-enrichment step was compared with filtration of the water sample. Cysts were recovered with two-color FCM. Those cysts hybridized with PNA and fluorescein isothiocyanate (FITC) were dual stained with monoclonal antibody (mAb) conjugated to phycoerythrin (PE); those not hybridized to PNA were dual stained with mAb-FITC and mAb-PE. Results: A fourfold increase in fluorescent signal intensity was obtained when combining the mAb-PE and PNA probe compared with two-color antibody staining. When combined with IMS, Giardia was successfully identified by FCM, with no false positives detected. Conclusions: Analysis-only FCM detection of Giardia in water is feasible. Further method development incorporating PNA probe hybridization after IMS is necessary.

Original languageEnglish
Pages (from-to)79-86
Number of pages8
JournalCytometry Part A
Issue number2
Publication statusPublished - Feb 2003


  • Flow cytometry
  • Fluorescent in situ hybridization
  • Giardia
  • Immunomagnetic separation
  • Monoclonal antibody
  • Peptide nucleic acid
  • Two color


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