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

Significance 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. Approach 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. Results 415nm-peaked light was associated with the maximum photokilling efficacy for all the considered strains. Other wavelengths have a minor or scant effect. Conclusions 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.