Repurposed bunamidine disrupts envelope energetics and induces ROS-mediated non-lytic killing.

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major public health threat due to its multidrug resistance, biofilm formation, and persistence, which collectively limit the effectiveness of current antibiotics. Here we characterize bunamidine hydrochloride (BUN), a repurposed benzimidazole derivative, as a potent anti-MRSA candidate. Across clinical and reference isolates, BUN displayed low MIC/MBC values (4–8 μg/mL), rapid bactericidal activity, and consistent efficacy in both planktonic and biofilm-associated populations. BUN eradicated persister cells within hours, while exhibiting a markedly reduced propensity for resistance development compared with ciprofloxacin. Mechanistic analyses revealed that BUN disrupts envelope energetics—causing membrane depolarization, collapse of the proton motive force, ATP depletion, and lipid disorder—without pore formation. These events triggered amplification of reactive oxygen species (ROS), which acted as critical execution factors for bacterial killing. Hemolysis assays confirmed selective compatibility with mammalian membranes, consistent with a non-lytic mode of action. In murine abscess and wound infection models, which represent early acute infection stages rather than established biofilm or chronic conditions, topical BUN treatment reduced bacterial burden, accelerated wound closure, and alleviated inflammation without apparent toxicity. These results demonstrate early therapeutic efficacy, tissue-protective, and anti-inflammatory effects in acute infection settings. While the current in vivo models support antibacterial efficacy during early infection, evaluation in established biofilm or chronic infection models will be an important direction for future studies.