Washington D.C. - The old maxim "you are what you eat" appears to apply to cows too, according to a new study which indicates that cattle diets may bear a great deal of responsibility for infection of humans with harmful strains of E. coli.
There are approximately 30 million cases of food-borne illness each year in the United States. In particular, scientists have been trying to understand why infections by certain harmful strains of the bacteria Escherichia coli (E. coli), which can be fatal, appear to be on the rise. In a study to be published in the 11 September issue of Science, a group of researchers from Cornell University show that cows fed grain instead of hay may be more likely to transmit dangerous strains of E. coli to humans.
Beef cattle are natural candidates for investigating the spread of pathogenic E. coli. The bacteria inhabit cows' gastrointestinal tracts (as well as our own), and are present in cattle feces. Feces are often thought to be the culprit behind infected hamburger meat as well as produce, since it is virtually impossible to prevent all fecal contamination of meat at slaughter, and fruits and vegetables can be contaminated when fertilized with cattle manure. In their study, Francisco Diaz-Gonzalez and his colleagues found that diet significantly affects the overall quantity of E. coli in cattle feces as well as the proportion of different strains of the bacteria, providing an improved environment for the harmful, or "pathogenic" variety.
Since World War II beef cattle have been fed large amounts of starchy grain and
very little hay. But since cattle don't have enough of a starch-digesting enzyme
to fully process this diet, the starch makes it all the way through the
digestive process to the colon, where it ferments. This acidifies the colon
environment, which E. coli inhabits. And, if E. coli is grown
under these acidic conditions, it can develop the extreme
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Contact: Diane Dondershine
ddonders@aaas.org
(202) 326-6421
American Association for the Advancement of Science
11-Sep-1998