Biomapping salmonella serovar complexity in broiler carcasses and parts during processing

Salmonella contamination of poultry remains a food safety challenge for broiler processors. The objectives of this study were to measure the efficacy of antimicrobial interventions in commercial broiler processing plants to reduce Salmonella and to assess changes in the Salmonella serovars before and after the chilling process. Three commercial processing plants were visited during 2020-2021 and 660 carcass rinse samples collected at three locations (before and after the pre-chiller, and after the main chiller) plus 80 drumstick samples across eight independent visits were collected and screened for Salmonella. Overall, Salmonella was detected in carcass rinse samples collected at 66% (145/220) pre pre-chill, 13.2% (29/220) post pre-chill and 2.3% (5/220) post-chill locations. Serovars Typhimurium, Infantis, and Kentucky were most commonly identified. CRISPR-SeroSeq was used to assess serovar populations and approximately 40% of carcasses (41.2% pre pre-chill and 37.0% post pre-chill) contained more than one serovar (range 1-4 serovars per carcass). Two out of five post-chill carcasses also contained multiple serovars. The low Salmonella incidence post intervention limited any conclusions about survival of particular serovars. Our data shows that serovar presence varies between flocks, even within the same broiler complex and CRISPR-typing also reveals evidence of multiple strains of the same serovar within a flock processed on the same day. We also compared Salmonella serovar populations across 128 paired samples (256 total samples), encompassing samples enriched in both RV and TT broths and found high concordance (Bray-Curtis <0.3) in 93% of samples. This study shows that antimicrobial interventions significantly reduce Salmonella on the carcasses during chilling and demonstrates effective use of a novel deep serotyping technology to track Salmonella serovars through processing.