New Vaccines May Help Thwart E. coli
By Marcia Wood
December 17, 2009
Immunizing calves with either of
two forms of a vaccine newly developed by Agricultural Research Service (ARS)
scientists might reduce the spread of sometimes deadly Escherichia coli
O157:H7 bacteria. The microbe can flourish in the animals' digestive tracts,
yet doesn't cause them to show clinical symptoms of illness.
In humans, however, E. coli can cause bouts of diarrhea and,
sometimes, life-threatening hemolytic uremic syndrome.
K. Sharma and
A. Casey developed the novel vaccines in their laboratories at the agency's
Animal Disease Center in Ames, Iowa and are seeking a patent for it.
Preventing E. coli O157:H7 from proliferating inside cattle helps
limit contamination of meat at the packinghouse, and reduces shedding of the
microbe into the animals' manure. Manure-borne E. coli can be moved by
rainfall into drinking water. What's more, it can end up in irrigation water,
and can contaminate fruits, vegetables or other crops, increasing risk of an
outbreak of foodborne illness.
One form of the vaccine is comprised of cells of a strain of E. coli
O157:H7 that is lacking a gene known as hha. A second form of the vaccine
contains an E. coli strain lacking both hha and a second gene, sepB. In
either vaccine, the E. coli strain produces a large quantity of what are
known as immunogenic proteins. These proteins trigger the immune system
response that prevents E. coli O157:H7 from successfully colonizing
In preliminary tests, Holstein calves were immunized at age 3 months with
a placebo or either form of the vaccine. Six weeks later, the animals
were given a dose of E. coli O157:H7, and, for the next 18 days, their
manure was tested for evidence of the microbe. Calves that received either
vaccine had reduced or non-detectable levels of E. coli in their manure
within only a few days after being inoculated with the bacteria, Sharma and
Some of the scientists' earliest work with the hha gene is documented in the
journal FEMS Microbiology
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture. The E.
coli investigations help ensure food safety, a USDA top priority.