Molecular Epidemiology of Salmonella enterica Serotype Dublin Isolated from 2011 to 2022 from Veal and Dairy Cattle in Pennsylvania

The emergence of Salmonella enterica serotype Dublin (S. Dublin) presents significant challenges to animal and human health. We analyzed 109 S. Dublin isolates from bovine submissions to the Penn State Animal Diagnostic Laboratory between 2011 and 2022. Using whole genome sequencing, we assessed their phenotypic and genotypic resistance patterns and correlated these traits with case histories and pathology reports. Core-genome analysis identified cgSTs with similar allelic profiles between our isolates and those from the U.S. and Canada, while some cgSTs were unique to our study. Histopathologic findings suggest a predominance of respiratory and gastroenteric/hepatic lesions, aligning with the histopathological case definition for S. Dublin infection. Critically, all isolates were multidrug-resistant, particularly to ampicillin (87%), ceftiofur (89%), chlortetracycline (94%), oxytetracycline (94%), enrofloxacin (17%), florfenicol (94%), sulfadimethoxine (97%), and trimethoprim (20%). Plasmid genomic analysis unveiled distinct plasmid types including virulence, resistance, and hybrid plasmids, carrying unique compositions of virulence genes and antimicrobial resistance. These findings underscore the importance of managing calf movement to control the introduction and dissemination of new cgSTs in Pennsylvania and potentially nationwide. Furthermore, they emphasize the urgent need to mitigate S. Dublin transmission, combat antimicrobial resistance, and enhance surveillance efforts to effectively protect animal and human health.