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This study investigated the epidemiology of Salmonella in a large-scale broiler slaughterhouse in Guangdong， China， and characterized the genomic features and potential transmission risks of the predominant serovar S.Infantis， providing evidence for targeted control. Comprehensive sampling was performed across all processing stages of the slaughterhouse， yielding Salmonella isolates that were tested for resistance to 12 antimicrobials using the agar dilution method. Thirty-four representative isolates were subjected to whole-genome sequencing （WGS） for analyses of serotype， multilocus sequence typing （MLST）， plasmid content， and resistance determinants， followed by construction of a single nucleotide polymorphism （SNP）-based phylogeny. In addition， 10 389 publicly available S.Infantis genomes were retrieved from NCBI to clarify the potential transmission risks using whole-genome multilocus sequence typing （cgMLST） and SNP pairwise distance matrix analysis. A total of 96 isolates were recovered， with an overall prevalence of 55.49% （96/173），and the highest prevalence observed in the evisceration stage （79.25%）. All isolates exhibited multidrug resistance （MDR） with highly similar resistance profiles， showing 100% resistance to ampicillin， ceftiofur， nalidixic acid， florfenicol， and sulfamethoxazole， and over 90% resistance to chloramphenicol and tetracycline. WGS revealed S.Infantis as the predominant serovar （32/34）， dominated by ST32 （30/32）. All S.Infantis isolates harbored the large IncFIB-type pESI megaplasmid， carrying diverse resistance， virulence， metal， and disinfectant resistance genes. Comparative genomic analyses indicated that the slaughterhouse isolates clustered closely with 15 global S.Infantis strains， 12 of which originated from human infections. These findings demonstrate extensive cross-contamination of Salmonella across slaughterhouse stages， with MDR S.Infantis strains harboring a wide repertoire of resistance and virulence determinants. The close phylogenetic relationship with international human-derived isolates underscores their strong transmission potential and public health threat. Enhanced monitoring and targeted control of MDR S.Infantis， particularly within poultry slaughterhouses， should be prioritized to protect food safety and public health.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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