Skin Infection Pathogenicity Associated with a Canine Microbiome Resident: Polygenic Architecture of Virulence Factors in Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is a common opportunistic pathogen in companion animals and a leading cause of skin and soft tissue infections (SSTIs). Despite its clinical relevance, the genomic determinants underlying pathogenicity and the transition from commensal carriage to invasive infection remain poorly understood. This study aimed to identify the genomic determinants of SSTI pathogenic potential in S. pseudintermedius and to determine whether pathogenicity is driven by single, major-effect virulence genes or by polygenic genome-wide genetic architecture. Using accessory gene-based and unitig-based genome-wide association studies (GWASs), employing a linear mixed model, across a genetically diverse collection of S. pseudintermedius isolates spanning multiple phylogenetic clades, we found that disease and carriage isolates showed no phylogenetic clustering. SSTI pathogenicity exhibited high narrow-sense heritability. Surface-associated LPXTG-anchored proteins, particularly spsF, harbored the strongest associations, with additional signals in iron metabolism (narH, sufB) and oxidative stress tolerance (ahpC). Random Forest classification validated GWAS signals. SSTI pathogenicity in S. pseudintermedius reflects a polygenic architecture driven by cumulative variation across surface-associated, metabolic, and stress-response loci, shifting focus from single virulence genes to genome-wide genetic variation.