Genomic diversity, antimicrobial resistance, and virulence profiles of Salmonella from retail pork under different supply modes in Jilin, China.

Salmonella is a major foodborne pathogen, with retail pork serving as a primary reservoir. This study investigated how fresh and chilled retail supply modes influence the genomic, antimicrobial resistance, and virulence profiles of Salmonella contaminating retail pork. Among 250 samples, 60 strains were isolated (24.00%). The chilled supply isolation rate was higher than that of the fresh supply mode (56.00% vs. 20.44%, P < 0.05), suggesting that the compound stressors inherent to chilled processing and storage may facilitate the survival and persistence of Salmonella. Antimicrobial susceptibility testing revealed the highest resistance rates against tetracycline (66.67%), with 61.67% of isolates classified as multidrug-resistant (MDR; resistance to ≥3 antimicrobial classes), a rate exceeding the 57.79% MDR prevalence previously reported among retail meat-derived Salmonella in southern China. ARGs mediating β-lactam and aminoglycoside resistance exhibited the highest prevalence. Notably, an elevated trend of ARG frequency was observed in isolates derived from the chilled pork supply mode compared to fresh sources. In the fresh supply mode, ARG abundance exhibited significant positive correlations with biocide/metal resistance genes and insertion sequence elements. Further Nanopore sequencing of two representative S. I 4,[5],12:i:- strains (B602, B653) featuring the broadest resistance spectra uncovered IncHI2/HI2A plasmids that concentrate multiple ARGs, suggesting a potential risk for the horizontal dissemination of multidrug resistance. The enrichment of Salmonella and ARGs within the chilled supply mode presents a substantial public health risk, emphasizing the urgent necessity for upgraded biocontrol and supply-mode-integrated measures, encompassing abattoir-level sanitation and cold-chain management to curb pathogen dissemination.