Whole genome sequencing of Salmonella in poultry from China reveals the presence of bla in different serotypes.

Salmonella is a significant zoonotic pathogen, which carries diverse antibiotic resistance genes (ARGs) and utilizes poultry as a major reservoir. It spreads along the farm-to-table continuum, posing risks of human salmonellosis and clinical infections. In this study, 144 Salmonella strains were isolated from 741 poultry samples across 23 provinces in China. Whole genome sequencing (WGS) identified 16 serotypes and 18 sequence types (STs); the main serotypes are S. Enteritidis, S. Kentucky, S. Indiana and S. Typhimurium. SNP analysis of S. Enteritidis and S. Kentucky revealed potential transmission events (SNPs < 10), which were concentrated in close provinces. Antimicrobial susceptibility testing provides information on antimicrobial resistance phenotype, with over 50 % exhibiting multidrug resistance (MDR). Bioinformatics analysis revealed 67 ARGs in all strains, including 6 bla-positive isolates. Nanopore sequencing revealed that bla genes in different isolates were located on IncHI2/ST3 plasmids or chromosomes. The ability of horizontal transfer was verified by inverse PCR and conjugation experiments. Notably, this is the first report of bla-positive S. Idikan. This study revealed Salmonella's current prevalence status in poultry from China and emphasized the transmission of bla in poultry, which can help guide the rational use of antibiotics and the formulation of relevant rules in poultry breeding.