Photo by Terry Arthur. Though you can’t tell just by looking at them, some of the cattle grazing in a pasture, or noshing high-energy rations in a feedlot pen, may be “supershedders”—meaning they shed high levels of pathogenic Escherichia coli—such as E. coli O157:H7—in their manure.
Supershedding could increase the amount of E. coli O157 that makes its way from pasture or feedlot pen into packinghouses where steaks, roasts, ground round, or other in-demand beef products are prepared.
Often referred to simply as “O157,” this bacterium is apparently harmless to cattle. But in people, it can cause vomiting, severe stomach cramps, diarrhea, or other illness, such as hemolytic uremic syndrome—a sometimes deadly form of kidney failure.
In the United States, O157 is associated with about 95,000 infections every year, according to estimates from the U.S. Centers for Disease Control and Prevention. Some of these infections are attributed to eating O157-contaminated ground beef that was not properly cooked. Findings from studies led by Agricultural Research Service microbiologist Terry Arthur may help keep beef safe to eat by adding to our knowledge of supershedding. Arthur is with the agency’s Roman L. Hruska U.S. Meat Animal Research Center in Clay Center, Nebraska.
The investigations may provide a scientifically sound basis for new and effective strategies to curb supershedding. What’s more, the studies are a step toward a longer term goal—shared by public health officials, food safety researchers, and beef producers, processors, and purveyors alike—of ensuring that no harmful E. coli occurs in any link of the beef-production chain—from ranch to fork.
What defines a supershedder?
Scientists generally agree that a supershedder is any animal that sheds 10,000 pathogenic organisms per gram of manure. “It isn’t the amount of manure that’s shed,” Arthur emphasizes. “It’s the amount of the pathogen in the manure.”
Supershedding is a transitory condition that researchers currently think lasts less than a month. Regardless of duration, the basic problem with supershedding is the same: the copious amounts of O157 in the manure don’t necessarily stay where the manure was deposited.
Instead, shedding may lead to spreading.
An animal that takes a soothing dust bath, for instance, may inadvertently roll over some E. coli-contaminated manure on the feedlot floor and end up with O157 cells stuck to its hide. Later, some of that manure-borne E. coli may spread to pen mates during the usual milling about. Or the microbes could be ingested during mutual grooming, another normal, everyday behavior of pastured or penned cattle.