Scientists Probe Why E. Coli Strain Is So Virulent

June 2, 2011

Richard Harris

Manfred Rohde
A couple of E. Coli bacteria captured in an image from the Helmholtz Center for Research on Infectious Diseases in Berlin earlier this week.

The bacterium that is causing all the trouble in Europe is similar to the dreaded E. coli that has caused occasional but deadly outbreaks in the United States and elsewhere in the world. But the strain that has struck Germany is not so well known to science.

That leaves researchers puzzling over exactly why it's causing so many deaths, and wondering how long the epidemic will last.

At least medical scientists know quite a bit about its method of attack.

"To produce disease it really has to do two things. It has to attach to the intestinal wall and it has to produce toxin that gets absorbed into the body," says Dr. Robert Tauxe at the U.S. Centers for Disease Control and Prevention.

The bacteria, formally known as E. coli O104:H4, actually produce the same toxins that come from the more familiar E. coli, O157:H7. But the germ in Europe uses a different method to attach to the intestine.

It's caused so many deaths that it's left medical researchers wondering whether the bacterium's method of attack is especially deadly or if it simply has spread to a whole lot of people.

"That's the key question," Tauxe says. "And the answer is not entirely clear."

This is somewhat uncharted territory. A Chinese genetics lab reported today that they actually sequenced the DNA of the germ, and they consider it a new variant. But Dr. Tauxe says the strain of E. coli is actually not entirely new.

"We have not seen outbreaks in contaminated food before," he says. "But there have been isolated cases identified in the past, in a number of different countries around the world."

Dr. Phillip Tarr from Washington University in St. Louis has seen more than his share of disease caused by this sort of bacteria. He's a pediatrician who has treated children afflicted with other dangerous strains of E. coli.

"What we think happens is the toxins get into the blood stream and injure the blood vessels," he says. "And the blood vessels form little clots, and there's impaired blood flow to organs throughout the body."

This condition is called hemolytic uremic syndrome, and it hits the kidneys hard. In Germany, 470 people have been diagnosed with this severe condition. Usually, Tarr says, more than half of people who get this disease need kidney dialysis.

"In almost all cases it's temporary," he says. "Dialysis lasts a median of about 8 days."

But dialysis doesn't save everybody, as is clearly the case in Europe. Tarr says obviously the first priority now is to figure out the best care for people currently sickened by the disease.

"After this is over we really need to determine how it could have been prevented, if possible, and how to prevent it in the future," he says. "And right now we need to know where it's coming from."

Surveys of people who got sick found they were more likely to have eaten fresh tomatoes, lettuce and cucumbers. But that doesn't prove that the disease is actually from vegetables. And even if investigators can prove that link, Tauxe from the CDC says that begs the question of where the vegetables came from.

"Tracing back the origin of fresh produce, we learned in this country can take a long time," says Tauxe. "And I'm sure it's the same in Germany."

The case could also be getting cold. People diagnosed today could have eaten bad food a week or two ago. And with that lag time, the epidemic will probably fizzle out slowly, Tauxe says.

If the contaminated food is a fresh vegetable, the normal food safety tips won't necessarily protect you.

"Unfortunately these bacteria tend to be sticky and it's difficult to wash them off fresh vegetables," he says. "And sometimes they're even inside."

So this is one time when boiled cabbage could actually start to sound like an appealing option.

Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.

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