In vitro photoinactivation of Pseudomonas aeruginosa and Staphylococcus aureus biofilm by a novel multi-dose LED-based illumination method

recently, an aerosolized light source has been proposed to photo-inactivate pathogens responsible for multidrug-resistant chronic lung infections. To maximize the light source in vivo photokilling efficacy, its emission spectrum was predicted by a semi-theoretical model. To confirm and upgrade the model with experiments, biofilm photoinactivation studies were performed. in vitro biofilms of P. aeruginosa and S. aureus (reference and clinical strains) were photo-inactivated by LED sources at 415, 445, 525 and 623nm. Non-uniform illumination protocol was employed to deliver different doses (10 to 110 J/cm2) in a single experiment. Photokilling efficacy was quantified by CFU counting. 415nm-peaked light was associated with the maximum photokilling efficacy for all the considered strains. Other wavelengths have a minor or scant effect. biofilm photoinactivation was studied as a function of both dose and illumination wavelength. Results are compatible with expected presence of endogenous photosensitizers (porphyrins) in the bacteria.