Heightened variability observed in resistance and virulence genes across salmonella Kentucky isolates from poultry environments in British Columbia, Canada

Abstract

Many niche-dependent barriers along the poultry production continuum favour the survival of certain Salmonella serovars over others. Historically, the presence of particular serovars has been determined by niche-specific genes which encode resistance to selective pressures such as host defenses and industrial antimicrobial practices. Over the past decade, Canada has witnessed unexplained shifts in the Salmonella landscape in the poultry sector. Several formerly minor Salmonella serovars, including S. Kentucky and S. Reading, have recently increased in prevalence in live chickens and turkeys, respectively, in British Columbia (BC). The purpose of this research was to investigate the genomic features of the top poultry-associated Salmonella spp. in BC, to probe for serovar-specific characteristics that could address the recently shifting balance of serovars along the poultry continuum. By examining the quantity and diversity of antimicrobial resistance (AMR) genes, virulence factors (VFs), Salmonella Pathogenicity Islands (SPIs), and plasmids across 50 poultry-associated S. enterica isolates using whole genome sequencing and antimicrobial resistance profiling, we have identified serovar-specific differences that likely influence niche survival. Specifically, isolates in our collection from predominantly human pathogenic serovars (S. I 4, [5], 12:i: , S. Typhimurium, and S. Enteritidis) were found to share the IncFIB(S) and IncFII(S) plasmids which carry important VFs known to aid in human host infection. Additionally, these strains held the lowest number of AMR genes, and the highest number of unique SPIs which also facilitate virulence. However, other serovars containing a greater diversity and abundance of resistance genes have been increasing across the poultry sector. S. Kentucky was found to carry unique AMR genes, VFs, SPIs, and plasmids that could bolster persistence in farm and processing environments. Overall, S. Kentucky also had comparatively high levels of intra-serovar genetic variability when compared to other prominent serovars from our collection. In addition, one of our two S. Reading isolates had high carriage of both AMR genes and VFs relative to other isolates in our collection. As the poultry-associated Salmonella landscape continues to evolve in Canada, future studies should monitor the genetic composition of prominent serovars across poultry production to maintain up-to-date risk assessments of these foodborne pathogens to consumers.