The prevalence and load of Salmonella, and key risk points of Salmonella contamination in a swine slaughterhouse in Jiangsu province, China

We investigated Salmonella contamination in a slaughterhouse in Jiangsu province (China) by analysing prevalences, loads, and serotypes of Salmonella isolates. In total, 480 samples were collected, with total prevalence of 25.4%. High Salmonella prevalence and load were observed at exsanguination and splitting stages (40.6% and 75.0%; 2.50 ± 0.94 and 2.24 ± 0.72 logMPN/m2, respectively), with low prevalence and load at dehairing, flaming, and chilling stages (2.5%, 5.0%, and 15.0%; 1.39 ± 0.42, 1.36 ± 0.31, and 1.38 ± 0.30 logMPN/m2, respectively). The Salmonella prevalence and load increased substantially from flaming to splitting stage. Six serovars were represented among 122 Salmonella isolates; S. Derby and S. Typhimurium were predominant and were subtyped using PFGE and CRISPR typing approaches. Fourteen PFGE clusters were identified, with discrimination indices (DI) of 0.929 and 0.976 for S. Derby and S. Typhimurium, respectively. Clusters A1, A2, B, C1, C3, C4, D1, F, I, J, L1, M2, and N2 indicated the isolates from same sampling visit were distributed in same cluster. Cluster D1 and K showed that the strains isolated from splitter and carcass swab-samples were highly resemble. Salmonella serovars with the same CRISPR type were mostly isolated after splitting (represented by Dercr 1, Dercr 2, Dercr 3, Tycr 1, Tycr 2, Tycr 3, Tycr 4, and Tycr 6). Our findings revealed that introduced Salmonella was the major source of swine carcass contamination; three slaughtering steps (polishing, rectal drilling, and evisceration) between flaming and splitting were important risk points for Salmonella release, post-splitting slaughtering processes were major contamination risk points, and the splitter was a contamination factor. Our data suggest routes for controlling Salmonella contamination in a swine slaughterhouse.