Distinct transmission routes of Salmonella enterica serovars during pig growth on farms

Non-typhoidal Salmonella enterica is a major foodborne pathogen, with pigs and pig-derived products serving as key transmission sources of human infection. In this study, we applied whole-genome sequencing (WGS) to investigate the prevalence, transmission dynamics and antimicrobial resistance of Salmonella throughout the pig growing process on four closely related pig farms in China. Core-genome single nucleotide polymorphism (cgSNP) analysis has been widely used to determine the genetic relationships among Salmonella isolates from animals and animal-derived foods. To our knowledge, this is the first study to apply cgSNP analysis for epidemiological tracing of Salmonella transmission across interconnected pig farms in China. A total of 1,211 samples were collected from one breeding farm and three commercial farms in China, yielding 249 Salmonella isolates with an overall prevalence rate of 20.6%. Serotyping and genomic analysis determined five serovars, primarily S. Rissen, S. Derby, and S. 1,4,[5],12:i:-. cgSNP analysis further classified S. Rissen, S. Derby, and S. 1,4,[5],12:i:- into different clusters and revealed different transmission routes. Antimicrobial susceptibility test (AST) showed that all major serovars exhibited similar multidrug resistance to ampicillin, tetracycline, and sulfamethoxazole-trimethoprim. These findings demonstrate that different Salmonella serovars spread via distinct transmission routes but share common antimicrobial resistance patterns in pigs, emphasizing the need for targeted control measures across pig production chain to reduce the public health risks associated with antimicrobial-resistant Salmonella.