Salmonella Dublin outbreaks in Brazilian cattle: clinical-epidemiological aspects, antimicrobial resistance, and comparative genomic analysis

ABSTRACT Salmonella enterica serotype Dublin is a major concern for livestock, particularly due to its high morbidity and mortality rates in cattle herds. In Brazil, limited research has explored the epidemiology of this serovar, including outbreak characterization, antimicrobial susceptibility profiles, and genetic similarity of isolates. This study aimed to describe the clinical and epidemiological features of confirmed S. Dublin outbreaks across multiple Brazilian cattle herds, as well as to assess antimicrobial resistance profiles, identify resistance genes, and evaluate genetic similarity among isolates. Between 2018 and 2025, S. Dublin outbreaks were confirmed on 19 farms, most of which (84.2%) were dairy facilities involving calves. In 57.9% of the outbreaks, calves aged 90–180 days were affected. Notably, 68.4% of the farms reported S. Dublin outbreaks following or coinciding with an increase in cases of bovine tick fever (babesiosis and/or anaplasmosis). The majority of isolates (79.5%) were resistant to at least one antimicrobial, and 20.5% were classified as multidrug-resistant. Among the resistance determinants identified, a point mutation in gyrA, detected in more than a quarter of the sequenced isolates, was particularly notable. Single-nucleotide polymorphism (SNP) and core genome multilocus sequence typing (cgMLST) analyses revealed marked genetic similarity among isolates from related outbreaks, highlighting the risk of introducing S. Dublin through the purchase of untested animals. A high similarity was also observed between outbreak isolates and strains previously associated with human infections in Brazil, underscoring the zoonotic potential of S. Dublin. IMPORTANCE Salmonella Dublin is a cattle-adapted serovar capable of causing disease and substantial economic losses in the livestock sector. In humans, this serotype is also associated with serious illness and has the highest reported fatality rate among Salmonella enterica serotypes. In this study, we aimed to describe 19 outbreaks of S. Dublin in cattle herds and to characterize the clinical and epidemiological features of the disease in cattle, given the scarcity of information in the literature. Alongside this, we sequenced at least one isolate per farm to investigate antimicrobial resistance genes, mobile genetic elements, and the similarity between our strains and those from bovine and human sources in Brazil and elsewhere. Overall, this is the first study to assess the clinical aspects of S. Dublin in cattle herds from tropical regions, accompanied by the antimicrobial profiles of these isolates and their genomic relatedness to strains isolated from human clinical infections.