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.