Effect of blue light at 410 and 455 nm on Pseudomonas aeruginosa biofilm.

Pseudomonas aeruginosa is an opportunistic pathogen resistant to many antibiotics, able to form biofilm and causes serious nosocomial infections. Among anti-Pseudomonas light-based approaches, the recent antimicrobial Blue Light (aBL) treatment seems very promising. The aim of this study was to evaluate the efficiency of blue light in inhibiting and/or eradicating P. aeruginosa biofilm. Light at 410 nm has been identified as successful in inhibiting biofilm formation not only of the model strain PAO1, but also of CAUTI (catheter-associated urinary tract infection) isolates characterized by their ability to form biofilm. Results of this work on 410 nm light also demonstrated that: i) at the lowest tested radiant exposure (75 J cm) prevents matrix formation; ii) higher radiant exposures (225 and 450 J cm) light impairs the cellular components of biofilm, adherent and planktonic ones; iii) light eradicates with a good rate young and older biofilms in a light dose dependent manner; iv) it is also efficient in inactivating catalase A, a virulence factor playing an important role in pathogenic mechanisms. Light at 455 nm, even if at a lower extent than 410 nm, showed a certain anti-Pseudomonas activity. Furthermore, light at 410 nm caused detrimental effects on enzyme activity of β-galactosidase and catalase A, and changes on plasmid DNA conformation and ortho-nitrophenyl-β-D-galactopyranoside structure. This study supports the potential of blue light for anti-infective and disinfection applications.