Calf-related environments are reservoirs of Salmonella enterica on northeastern United States dairy farms with a history of endemic Salmonella Dublin infection

Abstract Objective To identify calf-related environmental reservoirs of Salmonella Dublin on 25 dairy farms with a history of endemic infection in the northeastern US. We hypothesized that maternity pens and calf housing areas were reservoirs of S Dublin on such farms. Methods We used real-time PCR to detect Salmonella enterica in samples collected from dairy farm environments and subsequently cultured PCR-positive samples. All confirmed S Dublin isolates were subjected to antimicrobial susceptibility testing and whole-genome sequencing. A mixed-effects logistic regression model was used to evaluate the association between farm location and PCR positivity. Results Of the 678 environmental samples collected, 50.1% were PCR positive for S enterica . A mixed-effects logistic regression model revealed calf-related equipment (OR, 2.7; 95% CI, 1.4 to 3.7) and maternity pen areas (OR, 6.2; 95% CI, 4.0 to 9.8) to have increased odds of testing Salmonella PCR positive in comparison to calf housing areas. Additionally, we isolated and antigenically confirmed S Dublin from maternity pens and calf housing areas. Core genome variation assessment of these isolates revealed high genetic similarity to human isolates. Conclusions The results demonstrate that maternity pens and calf housing areas can harbor S Dublin. Additionally, phylogenetic analysis highlights the potential for this pathogen to spread among human, animal, and environmental reservoirs. Clinical Relevance Identifying maternity pens and calf housing areas as reservoirs of S Dublin can inform the development of targeted hygiene and biosecurity protocols for dairy herds with endemic infection.