Intimin Is Vaccine's Key Ingredient
The key ingredient of the oral vaccinedeveloped at the Bethesda
university's Department of Microbiology and Immunologyis intimin,
a protein on the outer membrane of the O157:H7 strain. The bacteria
need intimin to attach themselves to intestinal tissue.
Nystrom assisted with this study early on by showing that calves injected
with purified bacterial intimin would develop antibodies against it.
"This confirmed previous studies in mice that showed that intimin-specific
responses reduced adherence of E. coli O157:H7 bacteria to both
cultured tissue cells and to intestinal cells in the intact animal,"
Nystrom's work also revealed that intimin-fighting antibodies interfere
with E. coli O157:H7 colonization and lessen intestinal damage
in newborn pigs. Earlier studies found that pregnant pigs vaccinated
against bacterial intimin developed antibodies against it in their sera
and colostrum. Also, newborn piglets experimentally challenged with
a Shiga toxin-negative E. coli O157:H7 strain, and who ingested
colostrum from intimin-vaccinated pigs, had fewer of the inoculated
bacteria in their intestines than did piglets nursed by nonvaccinated
Microbiologist Alison O'Brien, who chairs the university department,
is working closely with Nystrom in efforts to prove that the vaccine
is effective in cattle and to develop a plant containing the vaccine
that cattle will eat. "We want an inexpensive, effective, easily
administered vaccine to prevent cattle from becoming infected with E.
coli O157:H7, thus blocking transmission of these organisms to humans,"
O'Brien says. Corn is a potential candidate for development into an
intimin-producing edible plant for livestock, she adds.
Nystrom says a vaccine directed against intimin will not affect colonization
by beneficial, non-disease-causing E. coli bacteria because these
bacteria do not produce intimin.
The vaccine was developed by Nicole A. Judge, a graduate student in
O'Brien's laboratory who transferred the gene that encodes for intimin
into a non-nicotine tobacco cell line. Tobacco cells are the standard
ones used to determine whether plants can express a foreign antigen.
In the lab, the cell line was freeze-dried into powder that was then
rehydrated with buffer, mixed with milk, and given to calves.
Nystrom explains that the vaccine as first created could not be produced
in sufficient quantities to make enough intimin to be effective in cattle.
Wayne Curtis, a Pennsylvania State University professor, was contracted
to address this problem. He successfully scaled up production of intimin-expressing
tobacco cells so that a vaccine could be effective for calves.
"E. coli O157:H7 is a very dangerous infection, and cattle
are an important source of it," says Nystrom. "One way to
reduce the risk of infections in humans is to reduce the level of these
bacteria at the source point. Through vaccines such as this one and
by pinpointing where the bacteria hide in cattle, we can contribute
greatly to making beef an even safer consumer product."By
Agricultural Research Service Information Staff.
This research is part of Food Safety (Animal and Plant Products),
an ARS National Program (#304) described on the World Wide Web at www.nps.ars.usda.gov.
Evelyn A. Dean-Nystrom
and William C. Stoffregen
are at the USDA-ARS National
Animal Disease Center, 2300 Dayton Ave., Ames, IA 50010-0070; phone
(515) 663-7376 [Nystrom], (515) 663-7844 [Stoffregen], fax (515) 663-7458.
"Targeting E. coli Infections at Their Source"
was published in the August
2004 issue of Agricultural Research magazine.