Antimicrobial Photodynamic Therapy of Resistant Bacterial Strains by Indocyanine Green and 809-nm Diode Laser

Objective: This research aimed to investigate the bactericidal effect of indocyanine green (ICG) with 809-diode laser on wild type and resistant strains of Staphylococcus aureus and Pseudomonas aeruginosa in vitro . Background data: ICG and 809 nm combination can be a powerful tool for the treatment of wound-infecting, antibiotic-resistant bacteria. Methods: The effect of ICG and 809 nm laser light on wild type and resistant strains of S. aureus and P. aeruginosa was examined in vitro . ICG concentrations and laser doses were initially optimized for wild type S. aureus and P. aeruginosa . After determining the most effective ICG concentrations with specified light dose, they were applied on resistant strains. Viable bacterial cells were counted by serial dilution method. Results: Photodynamic therapy (PDT) with ICG was totally efficient to kill all of these bacterial strains, and light/ICG alone did not cause any lethal effect on any of the strains. Optimum ICG laser doses varied with respect to the bacteria type: 84 J/cm 2 of light dose with 6 μg/mL of ICG concentration caused more than 95% killing of wild type S. aureus strains. The same bactericidal effect was achieved with a lower amount of ICG (4 μg/mL) on resistant strain S. aureus . Optimum parameters for 99% killing of wild type P. aeruginosa were 125 μg/mL ICG and 252 J/cm 2 of light dose. Similarly, their bactericidal effect was stronger on resistant strain; 100 μg/mL ICG with 252 J/cm 2 was enough to cause a 99% decrease in viable cells. Conclusions: The combination of ICG and 809 nm laser light was found as an effective antibacterial method to destroy antibiotic-resistant strains of gram-positive and gram-negative bacteria.