SNP matrix.

Salmonella Dublin is a serovar that causes severe infections and cattle. Despite the importance of this agent, research on achieving its elimination from dairy farms is limited, which complicates risk mitigation and control efforts. This study thus aimed to assess the prevalence of S. Dublin on a farm with a history of outbreaks, to understand the dynamics of the infection, characterize the antimicrobial resistance of the isolates, and evaluate their genetic similarity. Multiparous cows in the postpartum phase are nearly five times more likely to shed Salmonella sp. A total of 39 cases of fatal septicemic salmonellosis caused by S. Dublin were confirmed in calves aged 3–5 months. Antimicrobial susceptibility was evaluated in 45 strains of S. Dublin, with 48.9% of the isolates classified as multidrug resistant, including resistance to penicillin (48.9%), tetracyclines (42.2%), and fluoroquinolones (33.3%). Seven multidrug-resistant isolates were selected for genomic sequencing. Among the resistance determinants identified, a mutation in the gyrA gene, present in all sequenced isolates, was notable. Analyses of cgMLST and SNPs revealed that the isolates from healthy animals were closely related to those found in animals with confirmed cases of S. Dublin, confirming that the agent was circulating among healthy animals across various categories. A high similarity was also found between the isolates in this study and strains causing salmonellosis in humans in Brazil, thus reinforcing the zoonotic nature and possible epidemiological link between cattle, and the occurrence of this disease in humans.

都柏林沙门氏菌（Salmonella Dublin）是一种可引发牛严重感染的血清型。尽管该病原菌具有重要研究价值，但针对奶牛场清除该菌的相关研究仍较为匮乏，这使得风险防控工作的开展更为复杂。因此本研究旨在对具有暴发史的牧场中都柏林沙门氏菌的流行情况进行评估，解析该感染的传播动态，对分离菌株的耐药性进行特征分析，并评价其遗传相似性。处于产后阶段的经产母牛，其沙门氏菌（Salmonella）排毒概率几乎是其他牛只的五倍。在3至5月龄的犊牛中，共确诊39例由都柏林沙门氏菌引发的致死性败血症型沙门氏菌病病例。研究对45株都柏林沙门氏菌进行了药敏试验，其中48.9%的分离株被判定为多重耐药，包括对青霉素（48.9%）、四环素类（42.2%）以及氟喹诺酮类（33.3%）的耐药性。研究选取了7株多重耐药分离株进行基因组测序。在鉴定出的耐药决定因子中，所有测序分离株均携带的gyrA基因突变尤为值得关注。核心基因组多位点序列分型（core genome multilocus sequence typing，cgMLST）和单核苷酸多态性（single nucleotide polymorphisms，SNPs）分析结果显示，健康动物体内的分离株与确诊都柏林沙门氏菌感染动物的分离株具有高度亲缘关系，证实该病原菌在不同类别的健康动物群体中持续传播。本研究中的分离株与巴西引发人类沙门氏菌病的菌株也呈现出高度相似性，这进一步证实了该病原菌的人畜共患特性，以及牛群与人类该疾病发生之间潜在的流行病学关联。