Population structure and antibiotic resistance of Salmonella isolates from diseased poultry in Jiangxi Province, China.

Salmonella poses a significant threat to human and animal health. However, the relationship among population diversity, antibiotic resistance, and infection risk remains largely unexplored. In this study, 69 Salmonella strains were isolated from diseased poultry in Jiangxi Province from 2021 to 2024. Using whole-genome sequencing, serotype prediction, MLST, virulence and resistance gene analysis, antibiotic susceptibility testing, and mobile genetic element annotation, we characterized the diversity, resistance profiles, and transmission mechanisms of these strains. The results showed high diversity, with Salmonella enterica subsp. enterica serovar Typhimurium (>60%) and ST19 (62.31%) as the dominant serovar and sequence type, respectively. Several avian isolates were genomically similar to human isolates, indicating potential zoonotic risk. All strains harbored conserved core virulence modules, whereas accessory modules (e.g., cdtB, astA, pefA) varied and may affect pathogenicity. The multidrug resistance rate was 97.1%, with 100% resistance to erythromycin, tilmicosin and tiamulin, and resistance rates of 91.3%, 84.1%, and 71.0% to sulfonamides, enrofloxacin, and ceftiofur, respectively. Sixty-eight resistance genes were identified. Highly conserved antimicrobial resistance gene (ARG) modules (e.g., sul2-aph(3″)-Ib-aph(6')-Id-tet(A)) were shared between chromosomes and plasmids and were flanked by mobile elements such as Tn3 and IS3. Genomic islands (GIs) and plasmids in some strains carried resistance gene clusters highly homologous to those in pathogens from humans, pigs, and chickens, suggesting active horizontal transfer of resistance genes across hosts. This study revealed high diversity, prevalent multidrug resistance, and active horizontal transfer of resistance genes in avian-derived Salmonella from Jiangxi Province, emphasizing the need for cross-host resistance monitoring and antibiotic management within the 'One Health' framework.