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Bacteria Break Kidney Stone-Oxalate Link

Oxalate is a substance that can lead to the formation of kidney stones if absorbed from the diet too quickly.

At the National Animal Disease Center in Ames, Iowa, ARS microbiologist Milton J. Allison and chemist Albert L. Baetz have helped lay the groundwork for medical research that may offer some relief to people who suffer from kidney stones.

Some 20 years ago, Allison was one of the first researchers to study bacteria that can break down oxalates in livestock forages. Now, the two researchers are concentrating on an oxalate-degrading bacterium called Oxalobacter formigenes that lives in the digestive tracts of cattle, sheep, and humans.

"This bacterium consumes only oxalate for its energy and growth. It is able to live in the large intestine of humans—but not in the small—because it can't tolerate any amount of air," says Allison.

He and Baetz have isolated two oxalate-busting enzymes from the bacterium. Their collaborative research with Peter Maloney, a microbiologist at Johns Hopkins University in Baltimore, Maryland, provided an understanding of how the bacterium gets its energy and grows in the anaerobic environment of the rumen of cattle and the large intestine of humans.

Studies on the oxalate-degrading bacterium at ARS' Poisonous Plant Research Laboratory in Logan, Utah, helped solve a mystery for western cattle ranchers who have lost livestock to the lethal halogeton plant, also loaded with oxalate.

Halogeton infests rangeland in seven western states. Cattle and sheep grazing freely on the weed become severely ill and die. But researchers at Logan showed that sheep could safely graze small amounts of this toxic plant because bacteria in their stomachs break down the oxalate, making it harmless. (See "Grazing Poisonous Plants," Agricultural Research, May 1986, p. 6-10.)

Medical researchers suspect some humans may ward off formation of kidney stones because their intestines contain high numbers of oxalate-degrading bacteria. But like the cattle which consumed and absorbed too much oxalate at once, other people may have difficulty when too many oxalate-containing foods are eaten.

"Several other researchers have published data supporting the concept that oxalate use by these intestinal bacteria may protect people against kidney stone disease. But further medical studies to examine this relationship are needed," says Allison. — By Linda Cooke, ARS,

Milton Allison is in the USDA-ARS National Animal Disease Center, 2300 Dayton Road, Ames IA 50010; phone (515) 663-7200, fax (515) 663-7458.

"Bacteria Break Kidney Stone-Oxalate Link" was published in the October 1995 issue of Agricultural Research magazine.