Poultry Processing Interventions Reduce Salmonella Serovar Complexity on Postchill Young Chicken Carcasses as Determined by Deep Serotyping

Abstract

Nearly 20% of salmonellosis cases are attributed to broilers, with renewed efforts to reduce Salmonella during broiler production and processing. A limitation to Salmonella culture is that often a single colony is picked for characterization, favoring isolation of the most abundant serovar found in a sample, while low abundance serovars can remain undetected. We used a deep serotyping approach, CRISPR-SeroSeq (serotyping by sequencing the clustered regularly interspaced palindromic repeats), to assess Salmonella serovar complexity during broiler processing and to determine the impact of antimicrobial interventions upon serovar population dynamics. Paired hot rehang and postchill young chicken carcasses were collected from establishments across the United States from August to November 2022. CRISPR-SeroSeq was performed on Salmonella culture-positive hot rehang (n = 153) and postchill (n = 38) samples, including 31 paired hot rehang and postchill samples. Multiple serovars were detected in 48.4% (74/153) and 7.9% (3/38) of hot rehang and postchill samples, respectively. On average, hot rehang carcasses contained 1.6 serovars, compared to 1.1 serovars at postchill (Mann Whitney U, p = 0.00018). Nineteen serovars were identified with serovar Kentucky the most common at hot rehang (72.5%; 111/153) and postchill (73.7%; 28/38). Serovar Infantis prevalence was higher at hot rehang (39.9%; 61/153) than in postchill (7.9%; 3/38). At hot rehang, serovar Enteritidis was outnumbered by other serovars 81.3% (13/16) of the time but was always the single or most abundant serovar detected when it was present at postchill (n = 5). We observed 98.4% (188/191) concordance between traditional isolation with serotyping and CRISPR-SeroSeq. Deep serotyping was able to explain serovar discrepancies between paired hot rehang and postchill samples when only traditional isolation and serotyping methods were used. These data demonstrate that processing interventions are effective in reducing Salmonella serovar complexity.