Effect of antimicrobial photodynamic therapy with Radachlorin and a 660 nm diode laser on Pseudomonas aeruginosa: An in vitro study

•Photodynamic therapy with Radachlorin and 660 nm diode laser inhibits P. aeruginosa.•Energy density and rate of delivery interactions affect therapy efficacy.•Higher energy densities resulted in higher P. aeruginosa kill rates.•At a given energy density, low delivery rates were more effective than high rates. Pseudomonas aeruginosa is one of the most life-threatening pathogens in nosocomial environments. This study aimed to explore whether photodynamic therapy using a 660 nm diode laser and Radachlorin is an effective in vitro inhibitor of P. aeruginosa and determine what energy density and rate of delivery are the most impactful. Suspensions ofP. aeruginosa were obtained, inoculated in petri dishes with Radachlorin, and incubated for 30 min. Then, the laser light of a 660 nm diode laser was irradiated at varying energy densities and rates of delivery. Cell viability was evaluated after culturing. The combination of Radachlorin and the laser was more effective than Radachlorin or the laser alone (P < 0.05) in reducingP. aeruginosa and showed a killing rate of 95.8 % at an energy density of 5 J/cm2. In addition, the low rate of photodynamic therapy delivery group was more effective in inhibiting P. aeruginosa compared to the high rate of photodynamic therapy delivery group (P < 0.05). Within the limitations of thisin vitro study, we found that photodynamic therapy using a 660 nm diode laser and Radachlorin was effective for the inhibition of P. aeruginosa. In addition, energy density and rate of delivery are important factors to consider when using a 660 nm diode laser and Radachlorin to inhibit the growth of this organism.