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Abstract
Salmonella enterica is a leading cause of bacterial foodborne illness. Ubiquitous in nature, this pathogen is well characterized in food animals; however, the prevalence, diversity, and dynamics of Salmonella in the environment are understudied. This introduces concern of food safety threat spillover from environmental reservoirs such as wild birds and surface water. Recent outbreaks linked to wild birds and surface water demonstrate the need to identify sources of Salmonella in our food systems to reduce the incidence and severity of illnesses from environmental contamination. To better understand routes of Salmonella transmission at the environment agriculture interface, three studies were completed that aimed to assess prevalence and characterize Salmonella populations within environmental reservoirs. First, wild bird feces were collected from produce fields in the southeastern United States, identifying a low prevalence of Salmonella and a strong association of viable pathogen with fresh feces. Results of this study suggest, for the first time in this region, a limited food safety risk attributed to wild birds compared to studies on the West Coast finding a more significant risk. This led to identifying more likely routes of produce contamination, including surface water. Second, a two-year longitudinal surveillance study of four surface watersheds determined high Salmonella prevalence and serovar complexity, where modeling showed a positive correlation between both prevalence complexity to weather variables such as precipitation and humidity. The incidence of antimicrobial resistance and clinically relevant serovars within complex populations supports the need for consistent monitoring of surface water sources. Finally, a comparative study between two rivers in Pichincha, Ecuador found higher prevalence and complexity in the river within an urban environment compared to a river embedded in animal agriculture. This data highlights potential human health risks associated with contaminated surface water and suggests a need for continued surveillance. Overall, these studies have significantly improved our understanding of Salmonella ecology in various environmental reservoirs. Considerable knowledge gaps remain, such as more fully elucidating the complex influence of weather and physiochemical variables on Salmonella presence in surface water. Additionally, many wildlife reservoirs remain understudied, limiting our understanding of Salmonella ecology and transmission outside humans and food systems.