Dual charge metallo-catanionic formulation to fight acquired infections with antimicrobial photodynamic therapy using visible light

Abstract

The rising incidence of hospital-acquired infections and the increasing antibiotic resistance in bacteria are among the foremost challenges in the field of public health. Antibacterial Photodynamic Therapy (aPDT) has emerged as a promising alternative method for eradicating bacterial biofilms. Nonetheless, the limited ability of photosensitizers (PS) to penetrate bacterial cell walls and bacterial biofilms reduces their effectiveness in combating microbial activity. To address these limitations, we suggest formulations that incorporate common dyes such as Rose Bengal (RB) and Toluidine Blue (TB) as photosensitizers within vesicles. The self-assembled structures are formed from an aqueous mixture of two oppositely charged surfactants, creating metallo-catanionic vesicles. The innovative aspect here lies in the inclusion of a double-chain copper based metallosurfactant (bishexadecyltrimethyl ammonium copper tetrachloride (CuC II)) as a cationic component with anionic sodium dodecyl sulphate (SDS). The formation, stability and aggregation behaviour of the synthesized metallo-catanionic vesicles were estimated in the presence of cationic and anionic photosensitizers i.e. TB and RB, respectively. The confocal fluorescence microscopy confirmed the PS encapsulation into selected fractions SDS:CuC II (30:70) and (70:30). Further, in-situ singlet oxygen quantification was done using chemical trapping method which supports enhanced singlet oxygen quantum yields in the presence of metallo-catanionic vesicles. PS-loaded metallo-catanionic vesicles were further used in antimicrobial Photodynamic Therapy against Gram-negative bacteria Escherichia coli (E. coli). A tremendous decrease in bacterial growth was observed after applying a dose of PS (TB and RB) loaded metallo-catanionic vesicles in the presence of laser light irradiation. The colony forming unit (CFU) value decreases from 5.84 × 106 CFU/mL to nil with metallo-catanionic vesicles (SDS:CuC II) encapsulated with both TB and RB PS (light dose 40 mins). Hence, our current research demonstrates that these dual-charge metallo-catanionic vesicles can serve as effective delivery vehicles for photosensitizers in photodynamic therapy to combat bacterial infections. Furthermore, these vesicles have potential applications in the field of photomedicine.