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 acid resistance necessary to survive the attack of the stomach acids which are supposed to protect humans from food-borne pathogens.
Diaz-Gonzales and his colleagues compared what is delicately termed the "digesta" of cows fed grain and hay. They found that cows fed grain harbored a greater number of E. coli bacteria in their colon, and that the bacteria were more acid resistant.
Since grain is cheaper and more fattening than hay, it's unlikely that livestock owners will stop feeding it to their cattle. However, feeding hay to cows even for a short period of time seems to reduce the quantity and virulence of the E. coli in their feces. So "cattle could be given hay for a brief period of time immediately before slaughter to significantly reduce the risk of food-borne E. coli infection," the researchers write.
ORDER ARTICLE #17: "Grain Feeding and the Dissemination of Acid-Resistant Escherichia coli from Cattle," by F. Diaz-Gonzalez, T. R. Callaway, M. G. Kizoulis, and J. B. Russell at Cornell U. in Ithaca, NY. CONTACT: James B. Russell at 607-255-3086 (phone), 607-255-3904 (fax), or jbr8@cornell.edu (e-mail).
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