The risk of E. coli infections in human beings could be vastly reduced by a simple change in the diets of cattle during the five days before slaughter, researchers say.
If confirmed in wide-scale testing, the results could help ease the concerns of the nation's hamburger devotees and fast-food makers.
In recent years, E. coli contamination of hamburgers and other products, from fruit juice to alfalfa sprouts, has led to many illnesses and deaths and prompted a number of product recalls. Last year, Hudson Foods Inc. exited the raw ground beef business after it was forced to withdraw a record 25 million pounds of suspect hamburger patties.
Researchers noted that this new strategy should not be viewed as a substitute for safe practices at beef-processing plants or wise handling and preparation of meat.
Starchy, grain-based cattle diets, which have become prevalent since World War II as producers sought to bring fatter cattle to market, promote the growth of Escherichia coli bacteria that can withstand the acidity of the human stomach and cause intestinal illness.
Researcher James B. Russell, a U.S. Department of Agriculture microbiologist stationed at Cornell University, said his research could offer an easy solution to that problem. By switching cattle to a diet of hay for a few days before the animals are killed, he said, feedlot operators could dramatically reduce the number of harmful, resistant bacteria.
Cattle producers and feeders said they were intrigued by the research, published today in the journal Science, but they cautioned that such a drastic change in diet could upset animals' systems, leading to illness or an aversion to eating that could result in weight loss just before slaughter.
If not, said Mike Engler, vice president of Cactus Feeders Inc. in Amarillo, Texas, "this could be just a revolution."
Exposure to disease-causing variations of these bugs--notably, lethal strains of E. coli O157:H7--accounts for more than 20,000 infections and 200 deaths annually in the United States, the researchers said.
The deadly O157:H7 burst into the limelight in 1993 when four children died after eating contaminated Jack in the Box burgers.
Since then, the meat industry, fast-food restaurants and epidemiologists have struggled to find ways to keep dangerous bacteria out of the food system.
Cattle are fed starchy grain because it is cheaper and more fattening than hay. However, the animals digest starch poorly. Some undigested grain reaches the colon, where it ferments. That process, Russell said, produces a high proportion of E. coli that can survive stomach acid.
The carbohydrates of hay, on the other hand, are not so easily fermented. In tests on 64 beef and dairy cows, Russell and a team of Cornell colleagues found high numbers of acid-resistant E. coli in grain-fed animals and much lower quantities in cattle fed with hay or grass. Bacteria in the hay-fed cattle were destroyed by an "acid shock" that mimicked the workings of the human stomach.
"We were surprised by the magnitude of the difference and the speed with which we could reduce the effect," said Russell, who earned his doctorate at UC Davis.
One Cornell scientist said the dietary switch should not prove problematic for cattle. A brief period of hay feeding immediately before slaughter "should not affect either carcass size or meat quality," said Donald H. Beermann, a professor of animal science.
Gary L. Cowman, the aptly named executive director of quality assurance with the National Cattlemen's Beef Assn. in Denver, noted that Russell's team did not identify any E. coli O157:H7 specifically in the tested cattle. However, Cowman said, the thinking is that "most likely you could impact O157" along with generic E. coli.
Cowman said feeds other than hay, such as brewer's grains, might offer hope because they would not cause so abrupt a change. He said he expects "all kinds of projects to spring up" once the industry analyzes the Cornell work.
"We didn't have much science to give us clues at the production level" for how to handle the threat, Cowman said. "[This is] very sound science and gives us some focus. We're very encouraged."
Under a federal directive, processors have been implementing science-based testing procedures to bolster inspectors' traditional method of determining bacterial problems through sight and smell.
Some meat plants are using steam pasteurization; others are considering low-level radiation, but that method has met with concerns from the public.
So far, the most reliable way of ensuring safety in hamburgers is to cook them thoroughly at 160 degrees. Heat kills the bacteria, but refrigeration does not.
Most types of E. coli are not harmful. The bacteria normally live in the gastrointestinal tracts of people and cattle. However, some strains produce toxins and can cause illnesses in human beings, ranging from bloody diarrhea to kidney failure or even death.
Only a small percentage of cattle in the United States carry E. coli O157:H7, and mature cattle are unaffected by it. But they can shed bacteria in their feces.
When beef carcasses are accidentally contaminated by feces at slaughter, dangerous bacteria can enter the food supply.