Progress 12/15/00 to 12/31/04
Outputs
We determined that intimin is an important colonization factor in the ruminant gastrointestinal tract. Significantly more sheep inoculated with the wild type strain or a complemented mutant, were still colonized after 2 months compared to those inoculated with an intimin mutant. When both sheep and cattle were dually inoculated with the wild type strain and the intimin mutant, significantly more animals of both species shed the wild type strain at 2 months post inoculation. Contrary to our hypothesis, the presence of Shiga toxin did not appear to influence the magnitude or duration of E. coli O157:H7 colonization in ruminants. Sheep inoculated with the wild type strain, an isogenic Stx mutant or a stx-phage mutant did not consistently demonstrate a different shedding pattern from one another. The mean competitive index (mutant/wt) was >0.5 at all 4 time points tested (1 wk, 2 wk, 1 m, and 2 m) in animals dually inoculated with an isogenic phage negative mutant and the
wild type parent strain.
Impacts
These conclusions are significant because the attaching and effacing lesions associated with intimin in pathogenesis models are rarely seen in mature ruminants. Our data suggests that they probably occur, but in numbers that are too low to detect microscopically. In addition these experiments validate the use of sheep as a model for the carrier-shedder state of E. coli O157:H7 in cattle. We did not detect any consistent differences in colonization (magnitude or duration) by E. coli O157:H7 between mature sheep and cattle.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Sheep were dually inocualted with the wild type E. coli O157:H7 and an isogenic stx-phage deletion mutant and monitored for intestinal colonization for 2 months post inoculation. There were no consistent statistical differences in either the magnitude or duration of intestinal colonization between the wild type strain and the phage deletion mutant.
Impacts
These results suggest that the presence of the stx-converting phage in the E. coli O157:H7 genome does not enhance or inhibit colonization of the organim in the ruminant gastrointestinal tract.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
Groups of sheep were inoculated with either wild type strain of E. coli O157:H7, an isogenic Stx mutant (inactivated toxin), or an isogenic strain with the entire stx-converting phage deleted. Preliminary results suggest that the strain missing the lysogenized phage may not colonize sheep to the same extent as the wild type strain. Trials are currently in progress to verify these results.
Impacts
If these preliminary data are confirmed this would suggest that the lysogenized Stx-producing phage somehow contributes to the fitness of the bacterial host.
Publications
- Cornick, NA, V Sharma, and HW Moon. 2002. Role of the Shiga toxin in the ecology of Escherichia coli O157:H7. 3rd Joint RRI-INRA Gastrointestinal Tract Microbiology Symposium, P-38.
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Progress 01/01/01 to 12/31/01
Outputs
Trials were conducted in which 3 groups of sheep were inoculated with either wild type E. coli O157:H7, an isogenic intimin mutant or the mutant complemented with the eae (intimin) gene on a plasmid. The magnitude and duration of fecal shedding of the strains was compared. During the initial post inoculation (pi) period and at 2 weeks pi the wild type E. coli O157:H7 was recovered in significantly greater numbers than was the intimin mutant. At 2 months pi the wild type strain was recovered from several sheep but the mutant was not. The colonizing ability of the mutant was partially restored by complementation with a plasmid carrying the gene for intimin. In a second series of trials we inoculated cattle and sheep with both the wild type E. coli O157:H7 and the intimin mutant. Once again the wild type strain was recovered in significantly greater numbers and for a longer period of time than was the mutant. These results indicate that intimin facilitates colonization
by E. coli O157:H7 in ruminants and suggest that fecal shedding of the organism is not the result of continuous ingestion from an environmental source.
Impacts
These conclusions are significant because the attaching and effacing lesions that are associated with intimin mediated mechanisms in pathogenic models of E. coli O157:H7 disease have not been detected in mature, asymptomatic ruminants. Our results suggest that these lesions probably occur in numbers that are too low to detect using light microscopy. This work also validates the use of sheep as an experimental model for the carrier-shedder state of E. coli O157:H7 in cattle. Fecal shedding of both the wild type strain and the intimin mutant were not significantly different between cattle and sheep. This is important for practical reasons since sheep are generally easier to handle, require less space and are less expensive. These data provide rationale in support of targeting intimin as a potential vaccine candidate or other anti-intimin strategies directed towards decreasing E. coli O157:H7 colonization in ruminants. Studies suggest that for a given reduction of E.
coli O157:H7, such a reduction in live cattle would contribute more to the overall decrease of human exposure to E. coli O157:H7 than would a similar reduction of the organism on chilled carcasses or in ground beef.
Publications
- Cornick, NA, SL Booher and HW Moon. 2002. Intimin facilitates colonization by Escherichia coli O157:H7 in ruminants. Infect. Immun. (accepted)
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