The dynamic interplay between Staphylococcus pseudintermedius and canine immunity: mechanisms of pathogenesis,...

Staphylococcus pseudintermedius is a common commensal bacterium of dogs. It becomes an opportunistic pathogen when it evades the immune and exogenous antimicrobial control to cause pyoderma, otitis, and postoperative infections in dogs. The shift from colonization to invasive disease illustrates an interplay between bacterial virulence and host immune defense. S. pseudintermedius encodes adhesins, exoenzymes, and cytotoxins that facilitate attachment to epithelial surfaces, biofilm formation, and tissue invasion. The bacterium evades the host immune system through IgG-binding proteins, complement inhibition, NET degradation, and modulation of cytokine signaling therefore enabling persistent infection or recurrence, particularly in atopic or immunocompromised hosts. Given that mobile elements found in the genome of S. pseudintermedius may encode resistance and virulence genes, these factors may influence selection for lineages that are virulent and methicillin resistant. The animal host defends itself against S. pseudintermedius by keratinocyte inflammasome activation, neutrophil recruitment, and Th1/Th17 responses. Although these mechanisms drive bacterial clearance, they can cause tissue injury because of inflammation. Despite increased understanding of S. pseudintermedius pathogenesis, effective immunoprophylaxis remains elusive because of bacterial antigenic diversity. Recent research has identified conserved surface proteins and secreted toxins which can serve as candidate antigens for robust vaccine design. This review synthesizes current knowledge on S. pseudintermedius-host interactions, highlighting mechanisms of bacterial defense and evasion. Furthermore, we suggest gaps that warrant further research and outline strategies for immunotherapeutics and vaccines against canine staphylococcal infections.