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Zoonotic pathogens such as Salmonella enterica continue to be an important cause of illnesses in humans, and new genotypic variants of S. enterica continue to emerge as threats to public health. It is known that S.enterica cause asymptomatic persistent infections of livestock animals. These asymptomatic infections then pose a risk of food contamination and human disease. Also, there is a growing body of evidence that suggests that interactions between members of the gut microflora of livestock animals contribute to the health and well being of those animals. Furthermore, shifts in the gut microflora of livestock animals lead to a predisposition to become colonized with new microbes including zoonotic pathogens. Recent data support the hypothesis that as L. intracellularis induces lesions in the pig's ileum, these lesions result in an increase in the colonization of S. enterica leading to an increase in the quantity and duration in the shedding of S. enterica.
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The long-term goals of this project are to improve our understanding of the relationship between infectious diseases of livestock animals, the microflora changes associated with the disease, and the shedding of food-borne pathogens. Specifically we will investigate the relationship between Lawsonia intracellularis in pigs, the shedding of S. enterica, and the related microbiome changes associated with these infections.
NON-TECHNICAL SUMMARY: Food safety remains an important public health concern with an estimated greater than 76 million cases of food borne illnesses per year in the US. Most research on food safety has been directed toward the understanding of the interactions of single food borne pathogens with a single food animal host. Emerging data suggest that food safety issues are much more complex and are likely the combination of multiple factors and microbes (including food borne pathogens and bacteria that normally reside in the intestines). Furthermore, much evidences points to the naturally occurring bacteria in the intestinal tract of animals as a means to control food borne pathogens. In this study, we propose to begin to unravel the complex interactions between food borne pathogens and normal bacteria in the intestinal tract of food animals with the intent of identifying factors that predispose animals to become infected with food borne pathogens. We believe that this understanding will allow scientists to develop novel ways to prevent these infections in the first place by controlling the composition of the bacteria in the intestinal tract and in so doing, decrease the risk that the public will contract food borne illnesses.
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APPROACH: A controlled experimental field trial will be performed to elucidate the potential for L. intracellularis to increase S. enterica shedding levels in pigs. Pigs will be individually or dually challenged with L. intracellularis and S. Typhimurium and quantitative measurement of S. Typhimurium and L. intracellularis load measured using established culture protocols. This data will provide evidence that dual infection increases Salmonella load and therefore increases risk of food borne contamination for finished pork products. Microflora/microbiome shifts that occur between the different challenge groups will be determined using intestinal samples from singly or dually infected pigs using 16S rRNA gene detection. This detection will employ DNA extraction followed by PCR amplification of the 16S rRNA gene V3 region coupled with massively parallel pyrosequencing. Phylum through species determinations will be determined through bioinformatic analysis. In addition, we will include total metagenomic analysis of some samples as a means to determine whether selective pressure in vivo (infection with L. intracellularis) leads to metabolic changes in the microflora that contribute to changes in animal health associated with shedding of S. Typhimurium. A mathematical model will be developed that assesses the potential human health risks associated with L. intracellularis-induced disease and subsequent changes in S. enterica shedding and Salmonella contamination of meat. This approach is novel in that strict animal diseases are not typically considered human health risks. The model will use the data obtained in specific aims 1 and 2 as well as data that we have previously collected to determine the number of human cases of salmonellosis that can be attributed to pork, and the percentage of these cases that can be attributed to prior infection with L. intracellularis.