Clonal dissemination of ST19 Salmonella Typhimurium within a Chinese poultry breeding pyramid and One-Health implications.

Salmonella poses a major threat to global poultry production and food safety. However, the transmission dynamics of Salmonella within poultry breeding hierarchies and their implications for the One Health remain poorly understood. This study bridges this knowledge gap by conducting epidemiological surveillance and genomic analysis of ST19 S. Typhimurium across a poultry breeding chain in China, augmented by comparative genomics of publicly available strains from diverse ecological sources. From 1,047 samples collected in a breeding system in Fujian Province, we recovered 37 ST19 S. Typhimurium isolates. Genomic comparison showed high clonality (≤2 SNPs) across them, revealing clonal dissemination of ST19 S. Typhimurium within flocks in the poultry breeding pyramid. Evolutionary analysis with 845 public Chinese ST19 S. Typhimurium genomes revealed close genetic links between the clone from this study and human clinical strains across multiple regions in China, providing evidence of cross-species transmission between poultry and humans. Furthermore, comparative genomic analysis elucidated the significant role of IncHI2 plasmids in facilitating the dissemination of antimicrobial resistance (AMR). In conclusion, this study underscores the clonal spread of ST19 S. Typhimurium within the poultry breeding pyramid and highlights potential One-Health risks, providing a scientific reference for designing targeted interventions to mitigate Salmonella transmission across poultry production systems and human populations.