Investigating the Dynamics of Salmonella Contamination During Commercial Pork Harvest Using Qualitative and Quantitative Detection Methods

Animals can be reservoirs for pathogens such as Salmonella, creating the potential for cross-contamination during harvest. Antimicrobials are used to limit this risk, but validation of interventions in commercial settings can be challenging. The objective of this study was to develop a bio-map to evaluate the presence and concentration of Salmonella during harvest in commercial market hog facilities. Carcass swabs were collected from three commercial market hog facilities, five times a day for five days, at nine locations throughout harvest from exsanguination to chilling (N = 675). At each sampling interval, a single carcass was tracked through harvest by swabbing the ham, shoulder, and jowl. Samples were analyzed for quantitative and qualitative Salmonella using Gene-Up Quant (log₁₀ CFU/swab; limit of quantification (LOQ) = 1 log₁₀ CFU/swab) and Gene-Up SLM2 (present/absent; limit of detection (LOD) = 1 CFU/swab), respectively. Prevalence data were analyzed in R Studio using linear mixed effect models, with carcass as a repeated measure, and ANOVA with means separated by Tukey's HSD (p ≤ 0.05). Due to the limited number of quantitative results above the LOQ (n = 7; 1.15-1.56 log₁₀ CFU/swab), statistical analyses were not performed. Salmonella prevalence was impacted by facility (p = 0.006), location (p < 0.001), and the interaction between facility and location (p = 0.004). Across all facilities, Salmonella prevalence was highest on incoming pigs and decreased most significantly after external decontamination. These results indicate that while concentrations may be low, Salmonella contamination is prevalent throughout the pork harvest process, highlighting the need for effective detection systems to develop and evaluate process control strategies.