WSU receives federal grant to target genetics of E. coli in cattle

News
Mar 5, 2010
by WLJ

Some detective stories move forward, one lead taking an investigator to the next, right up to when the case is solved.

Then there are times when the detective looks back, picking through a thick file, returning to witnesses for another round of interviews, poring over old evidence with new eyes.

That’s what Tom Besser, professor of veterinary microbiology at Washington State University (WSU), hopes to do with the enigma of 0157:H7. Besser received $1 million from the federal Agriculture and Food Research Initiative to see if previous research into stopping the bacteria at its source—cattle—may be more effective once different strains of the disease are considered.

The E. coli bacterium infects an estimated 70,000 Americans a year, but researchers have yet to get a sure grip on preventing its spread. Health experts have worked on reducing the infection rate through a suite of improvements in meat handling and food preparation. But when only 10 E. coli cells can make a person sick, vigilance can only go so far.

Besser hopes to stop the bacteria by focusing specifically on beef and dairy cattle and the different types of E. coli they harbor.

“Cattle don’t get sick from this,” he said. “It doesn’t bother them. But that still doesn’t mean we can’t go into cattle and maybe do something to reduce their infection rate with 0157. And we think if we do, then depending on how important cattle are as a source for humans, the human rate should go down too.”

So far, he has seen promising work in reducing the rate with which cattle get infected. Vaccines, beneficial bacteria or “probiotics,” and certain feeds have had some good results in reducing the numbers of infected cattle. Researchers have also been struck by how much the bacteria seem to die off in the winter but march back with great force in the summer months.

Now Besser thinks researchers might see even more striking results if they take different E. coli strains into account.

Two strains tend to be particularly infectious, being found in 95 percent of the human illnesses. These are called clinical genotypes.

Another group of three strains, the “bovine-biased” genotypes, is found in only 5 percent of human illnesses.

But as researchers have tested the effectiveness of different vaccines, feeds and treatments, they didn’t determine which of the strains were involved, since the strain types had not been discovered when most of the work had been done.

“We’ve got 15 or 20 years of research on 0157:H7 in cattle and we don’t have a clue in any of those research projects whether we were measuring bovine-biased genotypes or clinical genotypes,” said Besser. “And those interventions that we studied—the vaccines and the probiotics, and the seasonal variation and everything else—it would be really helpful to know whether the bovine-biased genotypes behaved differently than the clinical genotypes for those things.”

A vaccine, for example, could cut incidence of 0157 in half. “That could be really good if the half that it’s cutting it by is mostly clinical genotypes,” said Besser.

But if the half being reduced is mostly bovine-biased genotypes, it is only affecting the cause of a small percentage of illnesses. “Then you’re probably not affecting the human risk at all,” he said.

“We’ve spent a lot of money over the years trying to investigate feeds and management systems and manure handling systems,” he said. “Now that we know about these genotype differences, I want to go back and say, ‘Well, maybe some of those interventions that looked effective really aren’t very effective and we should write them off. Or maybe some of them that didn’t look very effective actually were much more effective than we thought.’ And I don’t think this is a far-fetched possibility. I think it’s quite possible.”

The three-year USDA grant will cover work in finding genetic markers that clearly define differences in the five strains. Researchers will then use the markers to take a new look at the effectiveness of different treatments and strategies. The grant will also involve an outreach program aimed at improving the accuracy of 0157 information going to industry, health professionals, the media and policy makers. — WLJ

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