Comparison of Antimicrobial Resistance Profiles in Salmonella spp. from Swine Upon Arrival and Postslaughter at the Abattoir

Abstract

Antimicrobial resistance (AMR) developed by Salmonella within animals used for food products is a major global issue. Monitoring AMR in animals destined for slaughter is, therefore, critical. Abattoirs may serve as potential candidate checkpoints for monitoring resistance patterns on farms. A complicating factor, however, is the impact of lairage on Salmonella detected in pigs at slaughter. This study sought to compare AMR patterns in Salmonella spp. in swine collected upon arrival (fecal samples) at the abattoir with those at postslaughter (cecal samples) and evaluate the feasibility of using slaughterhouse samples for surveillance of prevailing AMR Salmonella on farms. Eighty-four Salmonella isolates were recovered from a large, midwestern U.S. abattoir between September and November 2013. Isolates were tested for phenotypic AMR to 12 antimicrobials using the broth microdilution assay. Whole-genome sequencing identified the AMR genes harbored by the strains. Significant differences were observed in the isolate phenotypes and genotypes; however, no significant difference was observed in genotypic resistance patterns. Hence, the AMR profiles of Salmonella spp. postslaughter cannot be predicted from preslaughter samples. Further research considering the genetic diversity of isolates and statistical power of the genotypic analysis is warranted to improve the performance of WGS-inferred antimicrobial susceptibility.

Keywords: Salmonella; antibiotic resistance; foodborne pathogen; swine; whole-genome sequencing.