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.
Highlights
In a current assessment the Centers for Disease Control and Prevention of the United States of America stated that antibioticresistant bacteria are causative for at least two million illnesses and 23,000 deaths per year in the U.S alone (Centers for Disease Control and Prevention, 2013)
Irradiation parameters for SAPYR were determined to irradiation with photodynamic inactivation of bacteria (PIB) 3000 for 600 s obtaining irradiance at sample-level of 50 mW/cm2, which corresponds to an energy dose of 30 J/cm2 and a number of 6.78 × 1018 absorbed photons
A formula is presented for calculation of the number of photons absorbed by a given PS upon irradiation by its corresponding light source
Summary
In a current assessment the Centers for Disease Control and Prevention of the United States of America stated that antibioticresistant bacteria are causative for at least two million illnesses and 23,000 deaths per year in the U.S alone (Centers for Disease Control and Prevention, 2013). In September 2014, the White House published a strategy paper where the rise of antibiotic-resistant bacteria was declared as a serious threat to public health and economy. Some of the goals outlined in this strategy paper were to promote judicious use of antibiotics and to accelerate basic and applied research on and development of novel therapeutic tools for combating bacterial resistance (The White House, 2014). Dentists are increasingly faced with situations, where they have to deal with refractory progressions of periodontal or endodontic infections caused by antibioticresistant pathogens (Al-Ahmad et al, 2014; Rams et al, 2014)
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