Antibacterial and antibiofilm efficacy of TMC647055 against methicillin-resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat to global health, necessitating the development of novel antimicrobial agents. In this study, we evaluated TMC647055, a previously described NS5B polymerase inhibitor, for its antibacterial and anti-biofilm activities against S. aureus. TMC647055 demonstrated potent activity against diverse S. aureus strains, with minimum inhibitory concentrations (MICs) ranging from 3.13 to 6.25 µM and minimum bactericidal concentrations (MBCs) of 12.5-25 µM. TMC647055 retained consistent efficacy across 10 clinical MRSA isolates representing different multilocus sequence types. Time-kill assays revealed rapid bactericidal action, with 8 × MIC achieving ≥ 3-log reduction within 6 h and near-complete eradication by 12 h. Serial passage experiments revealed only a modest increase in MIC (≤ 4-fold), indicating a low propensity for resistance development. Notably, TMC647055 exhibited strong anti-biofilm properties, reducing biofilm formation by > 80% at sub-inhibitory concentrations (0.25 × MIC) and effectively eradicating established biofilms with 4 × MIC treatment reducing viable cells by approximately two logarithmic units. Mechanistic investigations revealed that TMC647055 functions through total cellular ATPase inhibition, causing dose-dependent ATP accumulation without membrane disruption or oxidative stress induction. Importantly, the compound demonstrated good biocompatibility in mammalian cells and showed no acute toxicity in Galleria mellonella larvae. In a murine MRSA pneumonia model, TMC647055 treatment (10 mg/kg) achieved 80% survival and significantly reduced pulmonary bacterial burden, comparable to vancomycin efficacy. These findings demonstrate TMC647055 as a promising therapeutic candidate against MRSA infections, although further preclinical studies are required to confirm its potential for clinical application.