Staphyloxanthin-enriched extracts promote biofilm formation and oxidative stress resistance in <i>Staphylococcus aureus</i>

<i>Staphylococcus aureus</i>, an opportunistic pathogen of global health concern, presents a significant clinical challenge due to its escalating antibiotic resistance and biofilm-forming capacity. The biofilm matrix of <i>S. aureus</i> is enriched with carotenoids, primarily staphyloxanthin (STX), which function as virulence factors by scavenging reactive oxygen species and inhibiting antimicrobial peptides. In this study, we examined the impact of the methanol extract of <i>S. aureus</i> (MES) on biofilm formation. Our findings revealed that MES enhanced biofilm formation in <i>S. aureus</i> strains with inherently weak biofilm-forming ability by upregulating key adhesion genes (fibronectin-binding protein A<i>/fnbB</i>, serine-aspartate repeat-containing protein D, clumping factors A/B, elastin-binding protein, and <i>fib</i>) and downregulating autolysis-associated genes (<i>lytR</i> and <i>lrgA</i>). Furthermore, MES augmented the resistance of these strains to whole blood-mediated killing and improved their antioxidant capacity. To elucidate the role of STX, methanolic extracts were prepared from <i>crtM</i> and <i>crtN</i> mutants of the USA300 LAC strain and applied to biofilm-impaired strains. These experiments provided indirect evidence that STX in the methanolic extract is a critical mediator of biofilm promotion <i>in vitro</i>. Collectively, our results suggest a potential mechanistic link between STX in <i>S. aureus</i> methanolic extract and biofilm formation, offering novel insights for therapeutic strategies against <i>S. aureus</i> infections.IMPORTANCEOur findings demonstrate that the methanolic extract of <i>S. aureus</i>, predominantly comprising STX, augments biofilm formation and antioxidant capacity <i>in vitro</i>. These results not only offer novel insights into potential therapeutic strategies for <i>S. aureus</i> infections but also underscore the potential role of microbial secondary metabolites in interstrain interactions.