Objective To understand the serotype distribution, drug resistance, and drug resistance gene carriage of human-sourced Salmonella isolates in Deyang, Sichuan province, and provide evidence for the epidemiological surveillance, effective prevention and control of Salmonella infection, and rational use of antibiotics in clinical treatment of the infections.

Methods A total of 76 human-sourced Salmonella isolates, which were collected by Chinese Pathogen Identification Net in Deyang from 2023 to 2024, were used for serological identification, drug susceptibility testing, and whole-genome sequencing. The multilocus sequence typing (MLST) was performed by using PubMLST database, the drug resistance genes were analyzed by using ResFinder 4.7.2, and the whole-genome single nucleotide polymorphism (SNP)-based phylogenetic trees were constructed by using KSNP 4.1.

Results The 76 Salmonella isolates belonged to 11 serotypes, with the predominant serotypes being S. Typhimurium (59.21%) and S. Enteritidis (18.42%). The highest resistance rate was observed to ampicillin (65.79%), followed by streptomycin (57.89%) and tetracycline (50.00%). The most common resistance phenotype was chloramphenicol–sulfamethoxazole/trimethoprim–tetracycline–streptomycin–ampicillin (10.53%). The MLST identified 13 sequence types (STs), predominated by ST34 (31.58%), ST19 (26.32%), and ST11 (18.42%). ST8333 Salmonella was detected in Deyang for the first time. Whole-genome sequencing analysis revealed that the 76 isolates carried 66 drug resistance genes belonging to 13 categories. The predominant genes included aminoglycoside resistance genes aac(6')-Iaa (100.00%), aph(3'')-Ib (55.26%), and aph(6)-Id (53.95%), β-lactam resistance gene bla_TEM-1B (56.58%), and sulfonamide resistance gene sul2 (47.37%).

Conclusion S. Typhimurium and S. Enteritidis were the predominant serotypes of human-sourced Salmonella in Deyang, with ST34, ST19, and ST11 as the main STs. The isolates carried diverse resistance genes and exhibited multi-drug resistance, which warrants close attention in future prevention and control. Whole-genome sequencing can be used to accurately track resistance genes of Salmonella in Deyang for the effective improvement of the precise drug resistance surveillance and the development of targeted and scientific prevention and control strategies.