EPA And UC Researchers Find Bacteria That Can Destroy Giardia Cysts

June 09, 1998

Cincinnati -- Researchers with the U.S. Environmental Protection Agency and the University of Cincinnati have isolated and characterized a bacteria strain which can degrade the protozoan parasite Giardia lamblia, a common cause of waterborne, gastrointestinal illness. Mark Rodgers, microbiologist with the National Exposure Research Laboratory, at the EPA and Brian Kinkle, associate professor of biological sciences at UC, presented their findings during the recent meeting of the American Society of Microbiology meeting in Atlanta.

Giardia is found in surface waters such as lakes and rivers. It survives in the environment in a resistant cyst form, and although Giardia contamination is associated with sewage outflows, it can also be found in crystal clear mountain streams.

"There does seem to be an association with wildlife," said Kinkle. "It's been called 'backpacker's disease.' You can go to very pristine places and find Giardia."

Because Giardia is so common in surface water, Rodgers decided to sample streams and rivers around Greater Cincinnati looking for microbes which might be able to feed on the Giardia cysts. "It's always been known that the viability of cysts decreases over time in a natural environment. We were interested in knowing what kind of biological factors contribute."

Rodgers' hunch paid off, and he found a strain which could degrade Giardia in a creek that flows into Kentucky's Licking River. He then took the strain to Kinkle's lab for characterization by graduate student Stacy Pfaller. It turned out to be a member of the genus Flavobacterium.

"This is an interesting group of microorganisms," said Kinkle, "which is able to degrade macromolecules such as cellulose and chitin. They also have a distinctive type of gliding motility."

The Giardia cyst's outer layer is made of a macromolecule which most closely resembles chitin. Work in Rodger's lab demonstrated that the degradative bacterial strain had to be in direct contact with the Giardia cysts to destroy them. "It's not an exo-enzyme," said Kinkle. "If you shake the culture, the bacterial strain doesn't degrade the cysts."

The research is still in its preliminary stages, and further work is necessary to see whether the bacteria would be useful in drinking water treatment, perhaps by using the bacteria in water filters to degrade the chlorination-resistant Giardia cysts.

University of Cincinnati

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