Enhancing Photodynamic Therapy: Reserpine-Mediated Efflux Pump Inhibition for Improved Pathogen Deactivation with Methylene Blue and Nanoparticles

Efflux pumps are crucial membrane proteins in bacteria that actively expel toxic substances, including antibiotics. This study evaluated reserpine, an efflux pump inhibitor (EPI), in combination with silver nanoparticles (Ag NPs) and methylene blue (MB) to enhance photodeactivation of pathogens. Our results showed that reserpine significantly increased pathogen deactivation, achieving a 40% greater reduction in colony-forming units (CFUs) when used with MB alone, and a 90% reduction when combined with Ag NPs/MB. This indicates that reserpine disrupts bacterial mechanisms for expelling toxic agents.

We also investigated singlet oxygen production, finding that reserpine did not affect it. Different sizes of Ag NPs consistently showed improved deactivation rates with reserpine. Molecular docking calculations revealed that reserpine binds more strongly to the AcrB protein of the AcrAB-TolC efflux pump, with a binding energy of -9.4 kcal/mol, compared to MB's -7.2 kcal/mol. These findings suggest that reserpine effectively enhances photodynamic therapy (PDT) by blocking efflux pumps. Future research will explore its use with other nanoparticles and photosensitizers to combat multidrug-resistant infections.