Pteryxin disarms MRSA by suppressing the CrtN-staphyloxanthin axis and mitigates osteomyelitis-associated bone damage

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major public health concern because of its resistance to commonly used antibiotics and its association with severe infections. Staphyloxanthin (STX), a membrane-associated carotenoid pigment, contributes to MRSA virulence by protecting bacterial cells against reactive oxygen species and host immune clearance. CrtN, a dehydrosqualene desaturase, catalyzes an essential step in STX biosynthesis and represents a potential antivirulence target. In this study, an STX inhibition assay identified pteryxin (PTX), a natural coumarin derivative, as an inhibitor of STX production, with an IC₅₀ of 4.826 µg/mL (12.49 µM). At concentrations that did not measurably affect bacterial growth, PTX reduced STX-associated pigmentation, increased susceptibility to oxidative stress and whole-blood killing and altered membrane-associated properties of USA300. Biophysical analyses, including surface plasmon resonance, thermal shift assay, cellular thermal shift assay, and intrinsic fluorescence quenching, supported an interaction between PTX and CrtN. Molecular docking predicted a possible binding mode involving Arg330 and Ser349. PTX also improved survival in a Galleria mellonella infection model and attenuated bacterial burden and bone damage in an early-treatment rat model of MRSA-associated bone infection. These findings support PTX as a potential antivirulence agent that suppresses STX biosynthesis through a CrtN-associated mechanism.