Multicellular behavior and genomic characterization of Salmonella Typhimurium in animal-derived food chains in Xinjiang, China: Phenotypic resistance, biofilm formation, and sequence types.

Salmonella Typhimurium Is a globally significant foodborne pathogen that causes diseases in livestock and poultry, which can lead to human infections and fatalities through contaminated food. In this study, we investigated the prevalence of Salmonella Typhimurium in the animal-derived food chain in Xinjiang, China. Among 5075 samples, the detection rate of Salmonella was 8.26 % (419/5075). Of these isolates, 27.21 % (114/419) were identified as Salmonella Typhimurium. Phenotypic analysis revealed significant antibiotic resistance: 82.46 % (94/114) of the strains exhibited multidrug resistance (MDR), with high resistance rates to amoxicillin / clavulanic acid, ampicillin, and tetracycline. Congo red plate assays demonstrated that 62.28 % (71/114) of the strains exhibited multicellular behavior (RDAR morphotype). Biofilm formation assays indicated that 96.49 % (110/114) of the strains possessed biofilm-forming capabilities, with 18.18 % (20/110) showing strong biofilm formation. Notably, strains displaying multicellular behavior exhibited enhanced biofilm formation, and biofilm capability was positively correlated with antibiotic resistance phenotypes. Whole-genome sequencing of 40 representative strains identified four sequence types (ST19, ST34, ST99, ST128), with ST34 being the most predominant. Distinct host preferences were observed: ST34 strains originated exclusively from cattle and sheep, while ST19, ST99, and ST128 strains were isolated from geese and pigeons. Resistance gene profiling revealed that strains harboring resistance genes exhibited stronger resistance phenotypes, while ST99 and ST128 strains lacked detectable resistance genes. Plasmids R64, R478, and pKPC_CAV1321 were identified in cattle- and sheep-derived strains, whereas pSLT-BT and pSPCV plasmids were predicted in strains from geese and pigeons. Pan-genome analysis and phylogenetic reconstruction demonstrated distinct genetic clustering among ST types, with ST19 and ST128 showing closer evolutionary relationships. This study provides comprehensive insights into the prevalence, phenotypic characteristics, and genomic diversity of Salmonella Typhimurium in the animal-derived food chain in Xinjiang. Our findings contribute to region-specific pathogen control strategies, enhancing public health safety and consumer protection.