Sequence Types and Antimicrobial Resistance Profiles of Salmonella Typhimurium in the Food Chain in Singapore

<i>Salmonella</i> remains a significant foodborne pathogen globally with <i>S</i>. Typhimurium presenting as a frequently occurring serovar. This study aimed to characterize 67 <i>S</i>. Typhimurium isolates from humans, food, farms, and slaughterhouses collected in Singapore from 2016 to 2017. Using whole-genome sequencing analysis, the isolates were found to belong to either ST19 (<i>n</i> = 33) or ST36 (<i>n</i> = 34). ST36 predominated in human intestinal and chicken isolates, while human extra-intestinal and non-chicken food isolates belonged to ST19. Plasmids were predicted in 88.1% (<i>n</i> = 59) of the isolates with the most common incompatibility group profiles being IncFIB(S), IncFII(S) and IncQ1. IncFIB(S) (adjusted <i>p</i>-value < 0.05) and IncFII(S) (adjusted <i>p</i>-value < 0.05) were significantly more prevalent in ST19 isolates, while Col156 (adjusted <i>p</i>-value < 0.05) was more significantly found in ST36 isolates. ST36 isolates exhibited higher resistance to multiple antibiotic classes such as penicillins, phenicols, folate pathway inhibitors, aminoglycosides, β-lactam/β-lactamase inhibitor combinations, tetracyclines, and fluoroquinolones. Phylogenetics analysis suggested potential shared routes of transmission among human, chicken, farm and slaughterhouse environments. Taken together, this study offers a cross-sectional epidemiological insight into the genomic epidemiology and antimicrobial landscape of <i>S</i>. Typhimurium isolates in Singapore, informing strategies for future public health and food safety surveillance.