Prevention and Control of Shiga-Toxigenic Escherichia in Livestock

Escherichia coli O157:H7 and related STEC exist in two distinct biological
compartments or ecological habitats. The primary STEC habitat is the nutrient-rich,
homeothermic and generally hospitable, warm, moist gastrointestinal (GI) tract, while
the secondary STEC habitat is the nutrient-poor, growth-limiting and thermally
unstable external agricultural environment. Each of these compartments represents a
unique ecological system, survival within which depends on the outcome of
interactions between STEC and the other biotic and abiotic components. The fitness
of STEC within each of these environments influences their ability to infect other
animals, including humans, directly or through contamination of external materials.
Understanding the key factors that influence the ability of STEC to survive and
thrive under these disparate conditions is critical to rational design of
intervention strategies to control these important zoonotic food-borne pathogens.
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Intensive pre-harvest research efforts over the past decade have failed to identify
any reliable evidence-based information or technology to significantly reduce STEC
prevalence in livestock. Much recent evidence suggests that STEC are not only common
but that they are essentially normal intestinal microflora of livestock. There is no
historical scientific precedent for successful control or elimination of normal flora
from any animal or plant species, so pre-harvest STEC control will be neither simple
nor easy to achieve. The emphasis of past research efforts has been to look for
modifiable risk factors (the epidemiologic approach) and to attempt intervention
trials of naturally-infected or artificially-challenged animals, using fecal STEC
O157 shedding as the primary outcome of interest. The role of the non-STEC
indigenous microbial communities in both the primary STEC habitat (ruminant GI tract)
and in the ambient agricultural environment (secondary STEC habitat) have been
relatively unstudied. Furthermore, the STEC infected animal has been the
intervention target of most pre-harvest STEC research over the past decade, while
interventions targeting the secondary STEC habitat have been relatively ignored.
Thus, to address these past research deficiencies, we have selected for emphasis in
this proposal studies aimed at (1) understanding the interaction of STEC with the
indigenous microbial communities in the primary and secondary habitat, and (2)
interventions focusing on STEC reduction in the secondary STEC habitat.