Photodynamic Versus Sonodynamic Therapy In Vitro: AntimicrobialActivity of Liposomal Rose Bengal

PURPOSE: To compare the antimicrobial effect of Photodynamic (PT) and Sonodynamic Therapy (ST) applying Rose Bengal (RB) loaded in liposomes, intended for the treatment of skin infections. METHODS: Formulations with standard soy lecithin (TSRB) and water-soluble soy lecithin (TWRB) were prepared and characterized by: (i) FTIR-ATR and DSC, and measuring size, polydispersity index, and zeta potential; (ii) in vitro release and permeation tests, visualizing the distribution of RB in the skin by confocal laser microscopy; (iii) stability tests under different conditions; (iv) occlusion capacity tests; (v) determination of antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa; and (vi) cytotoxicity tests with HaCaT keratinocytes. RESULTS: Both formulations exhibited encapsulation rates > 93% and particle sizes < 100 nm. TWRB was more stable, delaying RB release (12.8 % at 8h) and facilitating its penetration into the skin. MRSA was inhibited with PT and ST. P. aeruginosa was inhibited with TWRB/ST. Viability was >80% in HaCaT keratinocytes treated with TWRB/PT; however, acoustic cavitation caused significant cell detachment, precluding cytotoxicity assessment in ST assays. DISCUSSION: TWRB exhibited good technological and stability properties, capable of delaying RB release while enhancing its penetration into the skin. Although MRSA (Gram-positive) was inhibited, the most interesting results were obtained with P. aeruginosa (a Gram-negative bacterium, difficult to eradicate), as TWRB/ST completely inhibited it at a lower concentration than the RB solution. CONCLUSION: The results, particularly with P. aeruginosa, provide a basis for further studies using this system.