Evaluation of Three Protocols of DNA Extraction for Detection of Giardia duodenalis in Human Fecal Specimens

Background: Nowadays a number of methods are used for the extraction of genomic DNA from fecal specimens. Identification and selection of an effective DNA extraction method is considered as one of the most important steps in molecular assays of Giardia duodenalis. Objectives: We compared the effects of 3 different DNA extraction techniques in PCR amplification of a specific area of SSU rRNA gene. Methods: A total of 20 fecal samples containing purified cysts were aliquoted in 3 sub-samples. DNA extraction was performed using the Phenol-Chloroform Isoamyl alcohol (PCI), QIAamp DNA stool mini kit, and YTA Stool DNA Isolation mini Kit. The quantity and purity of extracted DNA were compared. The potency of extracted DNA was tested. Results: The results showed that the most concentrated DNA was obtained from phenol/chloroform/Isoamyl alcohol method and the best purity based on comparing the ratio of A260/230 was obtained from QIAamp DNA stool mini kit. In this study the diagnostic sensitivity of QIAamp DNA stool mini kit, phenol/chloroform/Isoamyl alcohol, and YTA Stool DNA Isolation mini Kit methods was 60%, 70%, and 60%, respectively. Conclusions: The application of a proper DNA extraction method leads to obtaining reliable and reproducible results in molecular assays and supports treatment and control strategies of G. duodenalis. In this study, PCR amplification targeting a 350-bp fragment of SSUrRNA gene demonstrated phenol/chloroform/Isoamyl alcohol as the most efficient method.