Phylogenetics, Comparative genomics, and Knowledge Centralization of Salmonella Serovars
Salmonella is a major foodborne pathogen, responsible for a substantial burden of illness and mortality worldwide. While advances in whole genome sequencing have provided unprecedented resolution for studying Salmonella, traditional serovar-based classification remains widely used in epidemiology, surveillance, and industry. However, emerging evidence indicates that many serovars are polyphyletic, consisting of multiple independently evolved lineages with distinct ecological and epidemiological characteristics. This raises fundamental questions about how Salmonella serovars should be defined and tracked in the genomics era, as well as how such information can be effectively communicated to public health, academic, and industry stakeholders. Thus, in this dissertation, we present three studies that aim to improve our understanding of Salmonella serovars by characterizing their phylogeny, identifying genetic features associated with hypervirulence, and developing a centralized resource. Broadly, this work includes: (i) a comprehensive phylogenetic analysis of the 100 most common Salmonella serovars in the NCBI Pathogen Detection database, (ii) genomic and phenotypic characterization of a multidrug-resistant (MDR) clade of Salmonella Dublin linked to human clinical cases, and (iii) development of the Salmonella Serovar Wiki, a curated digital platform consolidating serovar-specific information for academia, industry, and public health. A key finding from the first study is that polyphyly is far more common among Salmonella serovars than previously identified. These results highlight the limitations of relying solely on serotyping for Salmonella surveillance, particularly in outbreak investigations where different lineages within a given serovar may differ in host range, virulence, or epidemiological significance. Meanwhile, to investigate the potential mechanisms of virulence in a clinically important lineage, we focused on Salmonella Dublin, a cattle-adapted serovar that disproportionately causes invasive infections in humans. Comparative genomics revealed that the human-associated group within the recently emerged MDR clade of Salmonella Dublin harbors distinctive genetic features in contrast to the non-human-associated group. These findings may facilitate future research on Salmonella Dublin’s enhanced pathogenicity in humans, such as using identified genetic markers in animal studies. Finally, we developed the Salmonella Serovar Wiki, an openly available, curated platform that aggregates key information on over 100 serovars, including their genomic traits, outbreak history, animal reservoirs, and geographic distribution. This tool provides researchers, public health officials, and industry professionals with a centralized knowledge base, aiding hypothesis generation, while addressing the need for transparent, continuously updated serovar-specific resources. Together, the three studies in this dissertation, ranging from understanding serovar phylogeny to characterize human-associated group in the recently emerged clade of Salmonella Dublin, provide benefits for Salmonella control (e.g., lineage-based surveillance), advance precision food safety, and ultimately improve public health. Beyond Salmonella, the methods and digital frameworks developed here may serve as models for addressing similar challenges in the characterization and communication of other foodborne pathogens (e.g., pathogenic Escherichia coli, Listeria monocytogenes).