Giardia ID^TM - DNA Fingerprinting of Giardia Species and Strains 

Determine Sources of Giardia Contamination.

Note: Cryptosporidium and Giardia detection and enumeration using EPA Method 1623⁵ is also available. For prices, click here.

Important Note: The website and the services offered are for environmental professionals. This website is only a cursory overview of the services offered. Source Molecular is not responsible for errors or omissions on the web site. Furthermore, clients must understand the limitations of the services before submitting samples. Please call beforehand to discuss service details and type of samples to be submitted.

Giardia is a protozoa parasite affecting the gastrointestinal tract of humans and animals. They are shed in feces in the form of an cyst. This protozoa can remain dormant for long periods in the cyst form. It becomes active upon entering a host.

During this protective state (i.e. cyst), Giardia is particularly difficult to remove from water systems. Ordinary water disinfection techniques cannot kill cysts, and even the best filtration systems allow occasionally a few organisms to pass through.

Giardia causes a medical condition known as Giardiasis. Infections may be asymptomatic or may cause diarrhea, nausea, abdominal cramps, fever, vomiting and headaches. Immunocompetent individuals will usually recover from the illness within several weeks. However, immunocompromised individuals, such as HIV/AIDS or cancer patients, may be unable to remove the parasites from their systems and as a consequence, suffer debilitating illness and possible death.

Recent advances in molecular biology techniques have allowed species and strains of Giardia to be identified.^1,4 To date, five Giardia species have been regarded as valid on the basis of host specificity, pathogenesis, and oocyst morphology. These include Giardia duodenalis (aka Giardia lamblia or Giardia intestinalis) in humans and a wide range of mammals, Giardia muris in rodents, Giardia agilis in amphibians, and Giardia psittaci / Giardia ardeae in birds.^{2, 3}  Modern molecular techniques have permitted Giardia duodenalis to be subdivided into different strains based on their genomes and morphology. These different strains can infect a wide range of mammals, including humans.

Accuracy of the results is possible because the Giardia species and strain identification method uses PCR DNA technology. PCR allows quantities of DNA to be amplified into large number of small copies of DNA sequences. This is accomplished with small pieces of DNA called primers that are complementary and specific to the genomes to be detected.

Through a heating process called thermal cycling, the double stranded DNA is denatured and inserted with complementary primers to create exact copies of the DNA fragment desired. This process is repeated rapidly many times ensuring an exponential progression in the number of copied DNA. If the primers are successful in finding a site on the DNA fragment that is specific to the genome to be studied, then billions of copies of the DNA fragment will be available for detection by gel electrophoresis.

The gel electrophoresis apparatus uses an electrical field to distinguish different DNA fragments according to their molecular weights. Lighter DNA fragments will move farther along the gel than their heavier counterparts. At the end of the procedure different bands of accumulated DNA fragments will aggregate at different parts of the gel. It is this accumulation of DNA fragments that creates a band on the gel. Researchers use these bands to distinguish genomes of microorganisms such Giardia.

The PCR analysis can be further refined with the use of restriction enzymes. These enzymes when introduced into a DNA extraction will cut the DNA into smaller fragments. Restriction enzymes are a powerful genomic tool because they will always cut DNA at exact locations. As such, banding patterns will be heavier or lighter depending on where the restriction enzyme found its cut sites on the DNA molecule. Restriction enzymes exploit small variations in genomic sequences to create different banding patterns.

Consequently, these banding patterns provide a reliable indicator of the presence or absence of different species and strains of Giardia. It has been shown that these species or strains are associated predominately with certain animal groups such as rodents or humans. By identifying these varieties of different Giardia, it is possible to determine sources of Giardia pollution. Since some Giardia species or strains are sometimes found in other animal groups, it is important however to strengthen the validity of the results with other microbial source tracking tests such as the Human Enterococcus ID^TM, Cow E. coli ID^TM, or Pig E. coli ID^TM services. Furthermore other species or strains of Giardia might be present in the sample that were not detected with the restriction enzymes used. Additional restriction enzymes or other genomic techniques should be used to identify other species or strains of Giardia that might be present in the sample.

¹ Mayer, CL, Palmer, CJ Evaluation of PCR, nested PCR, and fluorescent antibodies for detection of Giardia and Cryptosporidium species in wastewater Appl. Environ. Microbiol. 1996 62: 2081-2085.

² Wallis, PM, Erlandsen, SL, Isaac-Renton, JL, Olson, ME, Robertson, WJ, van Keulen, H Prevalence of Giardia cysts and Cryptosporidium oocysts and characterization of Giardia spp. isolated from drinking water in Canada Appl. Environ. Microbiol. 1996 62: 2789-2797.

³ Kuhn, Ryan C., Rock, Channah M., Oshima, Kevin H. Occurrence of Cryptosporidium and Giardia in Wild Ducks along the Rio Grande River Valley in Southern New Mexico Appl. Environ. Microbiol. 2002 68: 161-165.

⁴ G. Ionas, K.J. Farrant, P.A. McLenachan, J.K. Clarke and T.J. Brown Species Differentiation of Giardia by PCR OECD Workshop Molecular Methods for Safe Drinking Water, Interlaken, 1998: 1-6.

⁵ U.S. Environmental Protection Agency. 1999. Method 1623: Cryptosporidium and Giardia in water by filtration/IMS/FA. EPA/821/R-99/006. Office of Water, U.S. Environmental Protection Agency, Washington, D.C.