Proanthocyanidins inhibit methicillin-resistant Staphylococcus aureus by disrupting membrane integrity and reprogramming transcriptional pathways.

Proanthocyanidins (PACs) are promising antimicrobial agents due to their broad-spectrum biological activities and confirmed safety profile. However, their mechanisms of action against methicillin-resistant Staphylococcus aureus (MRSA) remain unclear. Therefore, this study aimed to systematically investigate the antibacterial effects and potential molecular mechanisms of PACs against MRSA using microbiological assays, membrane integrity and oxidative stress analyses, transcriptomic profiling, RT-qPCR, molecular docking, surface plasmon resonance (SPR) validation, and protein expression analysis. PACs inhibited MRSA growth (MIC 156-312 μg/mL), disrupted membrane integrity, and altered the expression of genes involved in fatty-acid biosynthesis and oxidative stress responses. The involvement of membrane damage and oxidative stress was further supported by rescue experiments using vitamin E and N-acetyl-L-cysteine. Transcriptomic and RT-qPCR analyses revealed significant changes in genes associated with fatty-acid biosynthesis, oxidative stress responses, antibiotic resistance, and virulence regulation. Moreover, PACs enhanced the susceptibility of MRSA to β-lactam antibiotics, reduced mecA expression, and decreased the protein levels of PBP2a, SarA, and MgrA. SPR analysis further supported a direct interaction between PACs and SarA. Overall, these findings suggest that PACs exert anti-MRSA activity through multiple mechanisms involving membrane disruption, oxidative stress induction, and modulation of resistance- and virulence-related pathways. PACs may therefore represent a promising natural antimicrobial agent or antibiotic adjuvant for the control of MRSA infections.