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/cm2 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/cm2 of light dose. Similarly, their bactericidal effect was stronger on resistant strain; 100 μg/mL ICG with 252 J/cm2 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.