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Cattle are considered to be an important reservoir for E. coli O157:H7. E. coli O157:H7
resides in the intestine of cattle, which intermittently shed this pathogen in their feces. Fecal
contamination of meats during processing of cattle causes significant economic losses to the cattle
industry and accounts for numerous outbreaks of severe diarrheal illness in humans. Moreover,
release of E. coli O157:H7-contaminated manure into the environment carries a potential risk for
contaminating ground water, fruits and vegetables. Several disease outbreaks have resulted from
consumption of vegetables (5), fruits/fruit juices (3), and drinking water (1) which presumably
become contaminated with E. coli O157:H7- containing manure. Reducing valence and shedding of
E. coli O157:H7 in cattle, therefore, may prove an effective pre-harvest strategy for reducing postharvest contamination of meats and for protecting water and agricultural products from E. coli
O157:H7 contamination.<P>
The objectives for this work is to use a modified strain of E. coli O157:H7 as a vaccine against E. coli O157:H7.
Findings: The major objective of our study was to test a modified strain of E. coli O157:H7 as a vaccine for reducing colonization of cattle intestine by E. coli O157:H7. The rational for this study was that vaccinating cattle with the modified strains would generate a stronger immune response against multiple virulence factors that enable E. coli O157:H7 to colonize cattle intestine. In the current study, weaned calves were administered the vaccine three times over a 6-week period. Following vaccination, calves were orally infected with a large dose of live E. coli O157:H7 and feces from these calves were monitored for shedding of E. coli O157:H7 for two weeks. Results of fecal monitoring showed that the vaccinated calves stopped shedding E. coli O157:H7 after 1 � 2 days of oral infection while the unvaccinated controls continued shedding O157:H7 for most of the test period. This research provides preliminary but useful information pertaining to the development of a vaccine strain for reducing E. coli O157:H7 colonization in cattle in controlled studies and provides a basis for evaluating the effectiveness of this vaccine in reducing E. coli O157:H7 contamination in cattle herds in natural settings.