Photodynamic Versus Sonodynamic Therapy In Vitro: Antimicrobial Activity of Liposomal Rose Bengal

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.

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.

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.

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.

The results, particularly with P. aeruginosa, provide a basis for further studies using this system.