Researchers link E. coli, ethanol by-productby Mark Steil, Minnesota Public Radio
The number of E. coli-related beef recalls jumped last year. And now federal researchers are investigating whether cattle feed made from a by-product of ethanol production promotes E. coli growth in cows. Prior research has established a link between E. coli and distillers grain, an ethanol leftover that's a popular source of cattle feed.
Worthington, Minn. — E. coli 0157 is the third leading cause of food-borne illness in the U.S. E. coli can cause vomiting, bloody diarrhea and, in rare cases, death. Most E. coli linked to illness starts in the digestive tract of cattle. It spreads to humans when manure contaminates food products or water sources. Leafy vegetables and ground beef are the most common food sources of the bug.
About three years ago researchers in Kansas found evidence that feeding cattle distillers grain promotes the growth of E. coli. A team at Kansas State University was studying the types of bacteria living in the feces of cattle. Kansas State microbiology professor T.G. Nagaraja was part of the group.
"And we happened to isolate E. coli 0157 from the feces of these cattle," said Nagaraja.
That in itself was not surprising. It's not uncommon to find these bacteria in cattle digestive tracts. But the results did contain a surprise. Some cows were more likely to have E. coli than others. Half of the test cattle were fed distillers grain, half were not.
"There were a significantly higher number of animals in the distillers grain group that were positive for E. coli 0157 compared to the control," said Nagaraja.
There was no obvious reason for this finding. Distillers grain itself does not contain E. coli. It's just part of the corn kernel. Ethanol production uses only the starch from corn. The rest of the kernel, generically called distillers grain, can be fed to cattle. Nagaraja said the connection between distillers grain and E. coli instantly seemed important to the research team.
"We were intrigued and I thought it was worth following," he said.
It's possible the distillers grain helps produce an environment in the cow's digestive tract that promotes E. coli development. So the Kansas State group did three more studies. Two of them again showed elevated E. coli levels in the distillers grain group. But a third study showed no link at all.
Even so, Nagaraja believes there is "some connection" between distillers grain and higher E. coli prevalence. He said the study that showed no link may underscore an important fact about the livestock feed.
"The distillers grain product is not a uniform product," said Nagaraja. "And it could vary from plant to plant, from batch to batch. And so some of the inconsistencies that we have observed may, in fact, be due to the product being not consistent."
Nagaraja said some distillers grain contains more nutrients than others, things like sugars, amino acids and vitamins. The differing components may explain why sometimes it seems to promote E. coli growth and sometimes it doesn't.
A later study at the University of Nebraska may indicate how much distillers grain is too much. The research found that low levels of distillers grain are not a problem. But the researchers found higher E. coli levels when the feed composed 40 percent or more of the animals' diet.
Some experts have raised the possibility that widespread use of distillers grain as feed contributed to a sharp jump in E. coli-related ground beef recalls last year. The recalls came as U.S. distillers grain production increased by more than 25 percent. Kansas State University researcher T.G. Nagaraja said right now there's no evidence that distillers grain played any role in the recalls.
But the issue has caught the attention of U.S. public health officials, who are monitoring research developments. Epidemiologist Anandi Sheth with the U.S. Centers for Disease Control and Prevention said last year's E. coli jump reversed a general decline in E. coli meat contamination.
"We need to investigate that area further to see what we can do to have that level of contamination keep decreasing instead of going up," said Sheth.
The federal government can restrict livestock feed, such as in the late 1990s when certain feeds were banned to head off "mad cow" disease.
At least one high-ranking U.S. Agriculture Department official, though, has said there are no plans to restrict distillers grain use, no matter what the department's ongoing research reveals. Undersecretary for Food Safety, Richard Raymond told the Des Moines Register newspaper that if there is a problem, it'll be up to the beef industry to solve it.
- Morning Edition, 06/10/2008, 6:50 a.m.