Abstract

Background:
Salmonella enterica serovar Tumodi (S. Tumodi) is an emerging multidrug resistance (MDR) pathogen with significant zoonotic potential. Despite its low global prevalence, it demonstrates a concerning ability to colonize diverse hosts, including poultry, swine, racehorses and humans.

Aim:
This study aimed to describe the MDR and virulence profiles in S. Tumodi isolated from food-chain sources by whole-genome sequencing (WGS).

Methods:
Three S. Tumodi strains were isolated from retail chicken meat (n=2) and a food handler (n=1) from 2019 to 2020 in Longhua District, Shenzhen, China. Antimicrobial susceptibility testing was performed using the broth microdilution method, and antimicrobial resistance genes (ARGs) and virulence profiles were analysed via WGS.

Results:
All three S. Tumodi strains exhibited extensive multidrug resistance, demonstrating resistance to 20-22 of the 26 antibiotics tested. The genome assemblies were of high quality, with an average genome size of 4.92 Mb, coverage depth of 263×, N50 of 15,687 bp and contig number of 105. Genomic analysis revealed a conserved resistome harboring blaCTX-M-55, sul1 and aminoglycoside-modifying enzyme genes, alongside strain-specific genes. Notably, one strain harbored the carbapenemase gene, blaNDM-5. Virulome profiling identified a highly conserved set of virulence determinants, including intact Salmonella pathogenicity islands SPI-1 and SPI-2, adhesion systems and flagellar motility genes. Plasmid analysis confirmed the absence of detectable plasmids in all three strains, suggesting the resistance and virulence genes were likely chromosomally integrated.

Conclusion:
These findings underscore S. Tumodi as a high-risk MDR serovar with adaptive virulence mechanisms enabling cross-species transmission. This highlights urgent needs for integrated One Health surveillance to curb zoonotic dissemination.

Key words: Antimicrobial resistance genes; Foodborne pathogen; Genomic surveillance; One Health; Virulence genes.