title: The impact of absorbed photons on antimicrobial photodynamic efficacy.
abstract: Due to increasing resistance of pathogens toward standard antimicrobial procedures, alternative approaches that are capable of inactivating pathogens are necessary in support of regular modalities. In this instance, the photodynamic inactivation of bacteria (PIB) may be a promising alternative. For clinical application of PIB it is essential to ensure appropriate comparison of given photosensitizer (PS)-light source systems, which is complicated by distinct absorption and emission characteristics of given PS and their corresponding light sources, respectively. Consequently, in the present study two strategies for adjustment of irradiation parameters were evaluated: (i) matching energy doses applied by respective light sources (common practice) and (ii) by development and application of a formula for adjusting the numbers of photons absorbed by PS upon irradiation by their corresponding light sources. Since according to the photodynamic principle one PS molecule is excited by the absorption of one photon, this formula allows comparison of photodynamic efficacy of distinct PS per excited molecule. In light of this, the antimicrobial photodynamic efficacy of recently developed PS SAPYR was compared to that of clinical standard PS Methylene Blue (MB) regarding inactivation of monospecies biofilms formed by Enterococcus faecalis and Actinomyces naeslundii whereby evaluating both adjustment strategies. PIB with SAPYR exhibited CFU-reductions of 5.1 log10 and 6.5 log10 against E. faecalis and A. naeslundii, respectively, which is declared as a disinfectant efficacy. In contrast, the effect of PIB with MB was smaller when the applied energy dose was adjusted compared to SAPYR (CFU-reductions of 3.4 log10 and 4.2 log10 against E. faecalis and A. naeslundii), or there was even no effect at all when the number of absorbed photons was adjusted compared to SAPYR. Since adjusting the numbers of absorbed photons is the more precise and adequate method from a photophysical point of view, this strategy should be considered in further studies when antimicrobial efficacy rates of distinct PS-light source systems are compared.
authors.affiliation: Department of Conservative Dentistry and Periodontology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Cieplik
authors.affiliation: Department of Conservative Dentistry and Periodontology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Pummer
authors.affiliation: Department of Dermatology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Regensburger
authors.affiliation: Department of Conservative Dentistry and Periodontology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Karl-Anton
authors.initials: KA
authors.lastname: Hiller
authors.affiliation: Department of Organic Chemistry, University of Regensburg Regensburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Späth
authors.affiliation: Department of Conservative Dentistry and Periodontology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Tabenski
authors.affiliation: Department of Conservative Dentistry and Periodontology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Buchalla
authors.affiliation: Department of Dermatology, University Medical Center Regensburg Regensburg, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Maisch
keywords: Methylene Blue; SAPYR; absorbed photons; antimicrobial resistance; biofilm; photodynamic