Purpose: Biofilms significantly contribute to the persistence and antibiotic resistance of Staphylococcus aureus infections. However, the regulatory mechanisms governing biofilm formation of S. aureus remain not fully elucidated. This study aimed to investigate the function of the S. aureus lineage-specific two-component system, desKR, , in biofilm regulation and pathogenicity. Methods: Bioinformatic analysis was conducted to assess the prevalence of desKR across various S. aureus lineages and to examine its structural features. The impact of desKR on S. aureus pathogenicity was evaluated using in vivo mouse models, including skin abscess, bloodstream infection, and nasal colonization models. Crystal violet staining and confocal laser scanning microscopy were utilized to examine the impact of desKR on S. aureus biofilm formation. Mechanistic insights into desKR-mediated biofilm regulation were investigated by quantifying polysaccharide intercellular adhesin (PIA) production, extracellular DNA (eDNA) release, autolysis assays, and RT-qPCR. Results: The prevalence of desKR varied among different S. aureus lineages, with notably low carriage rates in ST398 and ST59 lineages. Deletion of desKR in NCTC8325 strain resulted in decreased susceptibility to beta-lactam and glycopeptide antibiotics. Although desKR did not significantly affect acute pathogenicity, the Delta desKR mutant exhibited significantly reduced nasal colonization and biofilm-forming ability. Overexpression of desKR in naturally desKR-lacking strains (ST398 and ST59) enhanced biofilm formation, suggesting a lineage-independent effect. Phenotypic assays further revealed that the Delta desKR mutant showed reduced PIA production, decreased eDNA release, and lower autolysis rates. RT-qPCR indicated significant downregulation of icaA, icaD, icaB, , and icaC genes, along with upregulation of icaR, , whereas autolysis-related genes remained unchanged. Conclusion: The desKR two-component system positively regulates S. aureus biofilm formation in a lineage-independent manner, primarily by modulating PIA synthesis via the ica operon. These findings provide new insights into the molecular mechanisms of biofilm formation in S. aureus and highlight desKR as a potential target for therapeutic strategies aimed at combating biofilmassociated infections.
