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Four photosensitizers PS1a-PS4a consisting in multicationic ruthenium(II) phthalocyanines (RuPcs) have been evaluated in photodynamic inactivation (PDI) of multiresistant microorganisms. The RuPcs, bearing from 4 to 12 terminal ammonium salts, have been designed to target the microorganisms cytoplasmic cell membrane and display high singlet oxygen quantum yields. In addition, PS3a and PS4a were conceived to exhibit multi-target localization by endowing them with amphiphilic character, using two different structural approaches. Under low light regimes, the two hydrophilic PS1a and PS2a , as well as the amphiphilic PS3a show much stronger response against Gram-positive MRSA than that observed for the typical phthalocyanines designed for PDI, namely zinc(II) and palladium(II) complexes, as well as free-base Pcs. Besides, PS1a , PS2a and PS3a show remarkably high activity against the Gram-negative E. coli , although weak fungicidal character against fluconazole-resistant C. albicans . Contrasting, the structurally different, amphiphilic PS4a shows only slight activity for Gram-positive bacteria, despite its ability to cross cell membrane and reach internal organelles. Still, PS4a shows a positive synergistic effect against MRSA when combined with doxycycline, exhibiting an increased activity from about 1.5 to about 4.9 log reduction under the light dose of 30 J/cm 2 and the 0.125 mg/L subinhibitory dose of doxycycline. • Ruthenium Phthalocyanines show strong PDI response against multiresistant bacteria. • Multicationic PS1a , PS2a , PS3a RuPcs outperform other MPcs against MRSA and E. coli • Synergic activity with doxycycline enhances PS4a ′s limited PDI effect. • PS1a, PS2a, PS3a RuPcs show 5 log reduction in bacterial growth with low light dose.
Domínguez et al. (Fri,) studied this question.