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A sugar helps E. coli go down

Sugar present in red meat and dairy found to be a risk factor for E. coli infection

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1:25pm, October 29, 2008
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Some harmful strains of E. coli might rely on something sweet to do harm.

Taking a bite out of a favorite hamburger could mean absorbing a foreign sugar that can put a person at risk for future bouts of diarrhea-causing strains of E. coli – even if that burger doesn’t host the E. coli strains.

A study published online October 29 in Nature presents results from lab work suggesting that foodstuffs such as red meat and dairy products contain sugar molecules not naturally produced in the human body which toxins from E. coli bacteria may bind to, triggering the pathway that causes disease.

Mercedes Paredes of the University of Texas Health Science Center at Houston, a doctor not involved with the study who focuses on E. coli, calls this research an important step. “The outbreaks caused by these [strains of] bacteria have the potential to overwhelm acute care resources, even in countries with an advanced health care system.” Based on these findings, she says she hopes for a future treatment to prevent the initial binding from occurring.

The sugar molecules, called Neu5Gc, are absorbed by the body and incorporated into intestinal and kidney tissue — later serving as targets for the E. coli toxin, says study coauthor Ajit Varki, a microbiologist at the University of California, San Diego, in La Jolla.

“In general [these strains of E. coli] are vastly understudied,” explains Andy Benson, a microbiologist from the University of Nebraska–Lincoln. “Now you’ve got a scenario where the organism — the toxin — actually needs something from the food it’s carried in — that’s truly unique.”

The sugar could be a key mechanism in the pathway allowing E. coli to infect a person, even from one bad burger.

It is still unknown how the sugar accumulates or is broken down over time because scientists don’t know how the body takes care of it, Benson says. The sugar could stay around in the body and put people at risk for future infection if they later consume a food that carries one of the harmful strains of E. coli.

The scientists tested human gut and kidney cells steeped in these sugar molecules and discovered that the toxin was about seven times more likely to bind to these cells if the sugar was present. It is still “not clear how to extrapolate this precisely to the human body,” Varki says.

Varki says that a typical quarter-pound beef burger would have about 3 milligrams of the sugar. Because the amount of the sugar varies in foods like meat and dairy products, he estimates a typical American diet includes between 10 and 20 milligrams per day.

At the molecular level, when the sugar is present on cellular surfaces, one part of the toxin binds to the sugar and another component of the toxin enters the cell and deactivates a critical cell regulator — leading to disease, says microbiologist Travis Beddoe of MonashUniversity in Victoria, Australia, a coauthor of the study.

“It’s ironic that eating a particular food presensitizes you to toxins from the very same food — I don’t know of any other food like that,” Varki says.

The microbiologists do not know if avoiding meat and dairy would reduce the likelihood that the E. coli toxin would harm the body. But, Beddoe says, “the most common way to get infected with E.coli is through eating poorly cooked meat, contaminated water or unpasteurized milk.”

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