Photodynamic therapy (PDT) is an alternative antimicrobial treatment method. Different wavelengths of light sources
mostly in the visible spectrum have been investigated for antimicrobial Photodynamic Therapy. Even though the
wavelengths in near infrared spectrum have the advantage of higher penetration capability in biological tissue, they have
not been preferred for PDT because of their possible photothermal effect in biological tissues. In our previous studies,
the desired PDT effect was achieved with 809-nm diode laser and indocyanine green (ICG) on drug resistant pathogens.
In this study, it was aimed to investigate the influence of different output powers during PDT applications with 809-nm
diode laser to clarify whether there is a photothermal effect to kill the pathogens or only the photochemical effect of
photodynamic therapy. 4 different output powers (500 mW, 745 mW, 1000 mW, 1500 mW) were examined in Laseronly
and PDT groups of P. aeruginosa ATCC 27853 in vitro. In the PDT groups, a non-phototoxic ICG concentration
(50 μl/ml) has been chosen to eliminate the toxic effect of ICG and evaluate only the thermal effect of laser. Applied
energy dose (252 J/cm2) was kept constant by increasing the exposure duration (300, 240, 180 and 120 seconds
respectively). These output powers in Laser-only or PDT groups did not seem to cause photothermal effect. There was
not any significant decrease or increase on bacterial load after the applications with different output powers. Higher
output powers in PDT groups with the same ICG concentration did not cause any higher killing effect.