Grappling With E. coli
Only 8 years ago, a killer foodborne bacterial disease was relatively
unknown in the United States.
In fact, when USDA's Economic Research Service published a report on the
economic impact of major U.S. foodbome diseases in 1987, Escherichia
coli O157:H7 was not even included.
Then, in January 1993, four children died and dozens of children and adults
became ill from eating undercooked hamburgers contaminated with E. coli
O157:H7 bacteria at a fast-food restaurant in Seattle, Washington. It wasn't
the first time food scientists recognized O157:H7 infections, but the incident
focused research attention on the problem.
In March of 1993, a team of ARS scientists at the National Animal Disease
Center (NADC) in Ames, Iowa, began studying the relationship between E.
coli O157:H7 and other microbes that normally live in a cow's first
stomach, or rumen. Their findings will provide the basis for future studies on
the impact of pre-slaughter livestock feeding schedules on the presence of
pathogenic microbes such as E. coli O157:H7.
The members of this ARS teammicrobiologist Mark A. Rasmussen,
veterinary medical officer Brad T. Bosworth, and microbiologists William C.
Cray, Jr., and Thomas Caseyhave translated their research findings into
recommendations for livestock producers and marketers.
"We used data collected by Australian scientists who have studied the
effect of rumen fermentation on Salmonella bacteria and applied this
information to the O157:H7 problem," says Rasmussen. "Poorly managed
cattle that are subjected to dietary stress during transport and marketing
represent a high-risk group and may carry an unusually high number of
This stress occurs when cattle refuse feed or the feed is offered only
"In animals deprived of feed, the normal rumen microorganisms aren't as
active as they would be under everyday conditions of digestion," says
Rasmussen. "The normal microbial activity is what keeps the bad bugs at
He presented these findings and recommendations to the National Livestock
and Meat Board's blue-ribbon task force on E. coli O157:H7 in Atlanta in
Rasmussen recommends that producers and marketers minimize pre-slaughter
fasting stress by feeding animals regularly. This practice could do a lot to
maintain the normal balance of rumen microbes and suppress bacteria like E.
In other NADC studies, ARS microbiologist William C. Cray, Jr., has
developed an experimental model to study E. coli O157:H7 in healthy
cattle. In the last 2 years, he has established the pattern and duration of
fecal shedding of O157:H7 from cattle.
Cray's research has shown that O157:H7 doesn't make cattle sick and that
calves can shed more bacteria for longer periods of time than mature cows.
"The potential for calves to serve as reservoirs of E. coli
O157:H7 needs to be studied more thoroughly," says Cray.
Meanwhile, to quickly identify O157:H7, Bosworth and Casey are using
molecular biology to develop a PCR (polymerase chain reaction) method. PCR has
already been proved a useful tool in identifying several viruses, viroids, and
mycoplasma-like organisms directly from nucleic acid extracts. The method could
be useful in checking several samples simultaneously and in differentiating
O157:H7 from other E. coli strains. -- By Linda Cooke, ARS
Rasmussen are in the ARS-USDA
Food Safety and Enteric Diseases Research Unit , National Animal Disease
Center, Ames, Iowa 50010.
"Grappling With E. coli" was published
in the July 1995
issue of Agricultural Research magazine.