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Giardia displays intestinal fortitude.

Giardia displays intestinal fortitude

Microbes encounter few environments more hostile than the human small intestine. To survive, they must withstand onslaughts of enzymes, antibodies, bile detergents and acid baths -- all the while holding fast against a surging current of corrosive fluids. Yet this environment is what the protozoan pathogen Giardia lamblia comfortably calls home.

G. lamblia, a single-celled, pear-shaped parasite that clings to the lining of the upper small intestine, can bring on violent attacks of diarrhea, stomach cramps and nausea. Usually transmitted through contaminated drinking water or unsanitary personal contact, it has become a bane of the backcountry hiker and one of the most common infections in child day-care centers.

But how does it flourish in the inhospitable intestine?

The answer may lie in the parasite's versatile protein coating. In the June 1 JOURNAL OF IMMUNOLOGY, parasitologist Theodore E. Nash of the National Institutes of Health and his colleagues report that when they inoculate patients' intestines with G. lamblia, antigens on its protein surface rapidly mutate -- and, in doing so, nimbly sidestep the host's antibodies.

Nash's group and others have also detected an unusually rich proportion of the amino acid cysteine in the protein layer. Cysteine may form disulfide bonds, which in turn can form strong links between protein molecules, microbiologist Frances D. Gillin of the University of California, San Diego, and her colleagues speculate in the June PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol. 87, No. 12). "So if these cysteines form a network of [bridge-like] cross-links on the parasite's surface," Gillin says, "then that might explain how Giardia survives in the small intestine, where it's swimming around in a sea of degradation."
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Title Annotation:how Giardia lamblia survives in the small intestine
Publication:Science News
Date:Aug 4, 1990
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