- Animals: bovine
- Animal Products: dairy
- Animal Production: animal protection and health
Salmonella Dublin is a bovine-adapted pathogen that poses a significant threat to the sustainability of dairy cattle and to human health. Clinical presentations can vary from asymptomatic carriers to a virtually untreatable respiratory syndrome in calves. Increased frequency of antimicrobial resistant clinical isolates, particular from livestock, has been reported and complicates treating these infections further. Because these presentations result in underdiagnosis, the prevalence of S. Dublin is under-researched and likely underestimated. Given Pennsylvania’s position as a national dairy producer, determining the prevalence of S. Dublin in the state is paramount for mitigation and risk management. To estimate the seroprevalence of S. Dublin in Pennsylvania, we will randomly sample 900 farms and test their raw milk for antibody against S. Dublin. We will follow-up with antibody-positive farms to collect environmental samples to confirm the active presence of S. Dublin. Given the increasing challenge of treating antimicrobial resistant infections, phage therapy has emerged as a promising sustainable intervention. To explore this, we will also isolate candidate bacteriophages for potential phage therapy use against S. Dublin from milkhouse wastewater and manure lagoons. These results will be synthesized with additional information about S. Dublin clinical presentation, its increasing risk to dairy herd health, and actions farmers can take to manage these risks and maintain their herds. Findings from bacteriophage isolation will be communicated with other researchers. Together, these approaches will provide short-term contributions to the sustainability of dairy cattle in Pennsylvania and long-term directions for infection management of this emerging pathogen.
Project objectives from proposal:
Objective 1: Determine prevalence of Salmonella Dublin on dairy farms in Pennsylvania
While the ideal scenario would be to repeatedly sample all PA dairy farms on three separate occasions for accurate determination of the prevalence of S. Dublin, such experimental design is beyond this project’s scope. Thus, we will perform ELISA antibody tests at 900 randomly selected PA dairy farms to estimate the seroprevalence of Salmonella Dublin in the state. This initial screen will yield multiple outcomes. First, it will confirm the presence of Salmonella Dublin in PA dairy operations. The number of positive farms will provide an estimate of prevalence in the state. This knowledge will inform dairy producers of the need to implement risk management intervention strategies as applicable. Finally, fulfilling this objective will allow us to streamline downstream environmental sampling to only those farms seropositive for Salmonella Dublin.
Objective 2: Confirm active presence of Salmonella Dublin on farms with antibody-positive milk
Given the challenging nature of culturing Salmonella Dublin from environmental samples, selective enrichment and PCR-based testing will be used to determine its prevalence on 10 seropositive dairy farms. Based on the work of Cummings et al. 20184 in New York, we expect 0.9% of farms to be seropositive; however, we are in communication with PSU extension team and Penn State Diagnostic laboratory concerning Salmonella Dublin and will target farms that previously tested positive for this pathogen for environmental sampling of manure and calving area. Fulfillment of this objective will confirm active presence of Salmonella Dublin on dairy farms in PA.
Objective 3: Isolate and screen bacteriophages for potential therapeutic intervention
Salmonella Dublin is bovine-adapted and largely, multidrug resistant to antibiotics. In fact, most S. Dublin isolates are resistant to all antimicrobials labeled for treatment of respiratory infections in bovines in the US.2 These characteristics, in combination with general trends toward antimicrobial resistance, justify the need for alternative therapeutic interventions. Phage therapy is increasingly appreciated for its efficacy against multidrug resistant infections in human and animal hosts. Given the resistance of Salmonella Dublin to traditional intervention and the limitations of current preventative measures, phage therapy has the potential to complement existing interventions and improve animal health and production outcomes. We will isolate phages from environmental reservoirs and perform screening for possible candidate phages. This screen will identify phages targeting Salmonella Dublin, providing a phage population that can be further narrowed based on established phage therapy criteria.