Bi-functional Caulis polygoni multiflori inhibits Staphylococcus aureus and potentiates the activity of erythromycin in vitro

Staphylococcus aureus (SA), particularly methicillin-resistant Staphylococcus aureus (MRSA), represents a major clinical challenge due to its ability to form biofilms, which contribute to treatment failure and recurrent infections. This study evaluated the antibacterial and anti-biofilm activity of the water extract of Caulis Polygoni Multiflori (CPM) against clinical and standard strains of SA. CPM exhibited consistent bacteriostatic and bactericidal effects, with time-kill assays confirming rapid elimination of planktonic bacteria at 2×MIC. Mechanistically, CPM dose-dependently inhibited bacterial adhesion to fibrin and suppressed biofilm formation, though it did not disrupt pre-formed biofilms, likely due to poor penetration into the biofilm matrix. In combination studies, CPM showed clear synergistic or additive effects with erythromycin in broth microdilution assays, but not in disk diffusion tests, possibly reflecting limited diffusion of CPM components in solid media. Importantly, CPM’s activity was independent of bacterial resistance profiles. These findings indicate that CPM acts through both direct bactericidal activity and anti-virulence mechanisms, and represents a promising candidate for topical combination therapy against MRSA skin and wound infections. Further studies are needed to elucidate its molecular mechanisms.