GIARDIA

SOIL MICROBIOLOGY

BIOL/CSES 4684






This webpage was created by Sarah Boltz


1. Identifying Characteristics



The pictures to the left show the two different forms of Giardia lamblia (trichrome stain; oil immersion magnification, X 1000). The top left picture is the trophozoite form and the bottom left picture is the cyst form. 





2. Taxonomic Description:

The many species of Giardia are given a species name based upon the organism which they parasitize. G. lamblia (also called G. duodenalis) inhabits humans, G. muris inhabits rodents, and G. ardeae inhabits birds. Giardia are very unique organisms in that they have bilateral symmetry. There is great biological interest in the organism because of its early evolutionary position.  Giardia lacks many of the prominent organelles, such as peroxisomes and mitochondria that are characterisitic of eukaryotic organisms.  Although they do lack these organelles, they have many of the endomembrane protein transport systems of higher cells.

The life cycle of Giardia consists of a reproductive, trophozoite form that inhabits the intestinal lining of its host, and a cyst form that can exist outside of its host for quite some time.  The structures of these cells are quite different to ensure their survival in their extremely variable environments.

Giardia lamblia causes giardiasis in humans.  Symptoms include:  nausea, upper intestinal cramping or pain, flatulence, and explosive, watery diarrhea. The protazoa can be transmitted by contaminated drinking water, food, or fecal-oral transmission.  Backpackers, children in day care centers, and homosexuals are most prone to exposure.  Incubation time can be as much as two weeks before symptoms develop.

The diagram on the left shows the life cycle of Giardia lamblia.  Injested cysts excyst in the small intestine, releasing the trophozoite.  The trophozoite reproduces by binary fission.  The bile salinity and alkaline pH environment induce the change from trophozoite to cyst form.  The cyst is excreted by the host and remains in the environment until it is injested by another host.

3. Isolation and Ecology

Members of the genus Giardia are found in colonies attached to the intestinal linings of animals (trophozoite), in the feces of infected individuals (cyst form), or in contaminated water (also cyst form). They can survive temperature extremes ranging from the internal temperature of an animal body to fresh water down to 4 degrees Celsius.

There are several known methods for isolating Giardia.  Diagnosis in patients commonly involves examining several stool specimens collected 2-3 days apart. Wet, saline mounts of fresh feces generally allows doctors to view the sample under a microscope.  Giardia are easily identified by their falling leaf motion, fibrils present, and nucleic characteristics.  If this fails, biopsy tissue can be processed and stained by trichrome or Giemsa stain.  Enzyme immunoassay and fluorescent-anitbody monoclonal antigen detection systems can also be used for identification.  Five commercial products are commonly used for their extreme specificity and sensitivity to the organism; they include:  ProSpec T, GiardEIA, MeriFluor, Color Vue, and DD System.  These kits fall into the categories of enzyme immunoassays, immunofluorescence tests, and DFA tests. 

4. Additional Sources of Information:

Gillies, R.R., and T.C. Dodds, 1973.  Bacteriology Illustrated.  Longman Group Ltd., Great Britain.

Gillin, Frances D., David S. Reiner, and J. Michael McCaffery.  1996. Cell Biology of the Primitive Eukaryote Giardia Lamblia.  Annual Review of Microbiology.  50: 679-705

Murray, Patrick R., Ellen Jo Baron, Michael A. Pfaller, Fred C. Tenover, and Robert H. Yolken.  1995.  Manual of Clinical Microbiology, 6th Ed., ASM Press, Washington, DC.

Pickup, R.W. and J.R. Saunders.  1996.  Molecular Approaches to Environmental Microbiology.  Ellis Horwood Ltd., University Press, Cambridge.

5. Links to other Sites on Giardia:

 http://geocities.com/CollegePark/Lab/4551

 http://www.biosci.ohio-state.edu/~parasite/giardia.html

http://vm.cfsan.fda.gov/~mow/chap22.html


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