This study demonstrated that three important periopathogens are susceptible to aPDT-mediated killing, regardless of whether they are present in planktonic or biofilm form. Furthermore, a clear energy dose-dependence exists with this treatment that should to be taken into account when determining optimal treatment times in clinical application.

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Photodynamic disinfection (PDD) is a nonantibiotic approach to treating drug-resistant bacterial infections. Pseudomonas aeruginosa, an opportunistic pathogen, is problematic because of its propensity to develop antibiotic resistance and its ability to secrete a protective biofilm matrix. This study examined the ability of PDD to eradicate planktonic and biofilm cultures of P. aeruginosa in vitro. Planktonic P. aeruginosa cultures were briefly exposed to a methylene blue-based photosensitizer formulation and subjected to energy doses ranging from 1.7 to 20.6 J cm )2 using a 670 nm nonthermal diode laser. Biofilms were grown for 24 and 48 h and exposed to photosensitizer for 30 s before illumination with 13.2 or 26.4 J of energy. A single exposure of planktonic P. aeruginosa to photosensitizer at >15.5 J cm )2 resulted in 100% eradication (>7 log 10 reduction from control), an effect that could be decreased significantly in the presence of the singlet oxygen quenchers L L-tryptophan and sodium azide. Decreasing the energy dose below this threshold by varying both power density and illumination duration resulted in a dose-dependent decrease in bacterial kill. In addition, 24 h biofilm viability was reduced by 99% with single exposure and 99.9% with double exposure, while 48 h biofilm viability was reduced by >99.999% with both single and double exposures. This study shows that PDD is effective in eradicating planktonic and biofilm cultures of P. aeruginosa, supporting the concept that translation into clinical practice for indications such as otitis externa and wound disinfection is a viable option.

Background Chronic rhinosinusitis (CRS) is one of the most common chronic conditions in the United States. There is a significant subpopulation of CRS patients who remain resistant to cure despite rigorous treatment regimens including surgery, allergy therapy and prolonged antibiotic therapy. Antimicrobial photodynamic therapy (aPDT) is a non-invasive non-antibiotic broad spectrum antimicrobial treatment. Our previous in vitro studies demonstrated that aPDT reduced CRS polymicrobial planktonic bacteria and fungi by >99.9% after a single treatment. However, prior to human treatment, the effectiveness of aPDT to eradicate polymicrobial biofilms in a maxillary sinus cavity must be demonstrated. Objective The objective of this study was to demonstrate the effectiveness of a non-invasive aPDT treatment of antibiotic resistant biofilms known to cause CRS in a novel anatomically correct maxillary sinus in vitro model using an enhanced photosensitizer solution. Methods Antibiotic resistant polymicrobial biofilms of Pseudomonas aeruginosa and MRSA were grown in an anatomically correct novel maxillary sinus model and treated with a methylene blue/EDTA photosensitizer and 670nm non-thermal activating light. Cultures of the biofilms were obtained before and after light treatment to determine efficacy of biofilm reduction. Results The in vitro maxillary sinus CRS biofilm study demonstrated that aPDT reduced the CRS polymicrobial biofilm by >99.99% after a single treatment. Conclusions aPDT can effectively treat CRS polymicrobial antibiotic resistant Pseudomonas aeruginosa and MRSA biofilms in a maxillary sinus cavity model.

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