Phenalen-1-one-Mediated Antimicrobial Photodynamic Therapy: Antimicrobial Efficacy in a Periodontal Biofilm Model and Flow Cytometric Evaluation of Cytoplasmic Membrane Damage

Abstract

In light of increasing resistance toward conventional antibiotics and antiseptics, antimicrobial photodynamic therapy (aPDT) may be a valuable alternative, especially for use in dentistry. In this regard, photosensitizers (PS) based on a phenalen-1-one structure seem to be especially favorable due to their high singlet oxygen quantum yield. However, the actual target structures of phenalen-1-one-mediated aPDT are still unclear. The aim of the present study was to investigate the antimicrobial efficacy of aPDT mediated by phenalen-1-one derivatives SAPYR and SAGUA for inactivation of a polymicrobial biofilm consisting of three putative periodontal pathogens in vitro and to get first insights in the mechanism of action of phenalen-1-one-mediated aPDT by assessing damage of cytoplasmic membranes. aPDT with SAPYR exhibited identical antimicrobial efficacy as compared to chlorhexidine (CHX) [4.4–6.1 log10 reduction of colony forming units (CFUs) depending on bacterial species] while aPDT with SAGUA was less effective (2.0–2.8 log10). Flow cytometric analysis combined with propidium iodide (PI) staining revealed no damage of cytoplasmic membranes after aPDT with both phenalen-1-one derivatives, which was confirmed by spectroscopic measurements for release of nucleic acids after treatment. Spectrophotometric PS-uptake measurements showed no uptake of SAPYR by bacterial cells. Despite the inability to pinpoint the actual target of phenalen-1-one-mediated aPDT, this study shows the high antimicrobial potential of phenalen-1-on mediated aPDT (especially when using SAPYR) and represents a first step for getting insights in the mechanism and damage patterns of aPDT with this class of PS.

Antimicrobial efficacy of alternative compounds for use in oral care toward biofilms from caries‐associated bacteria in vitro

“…() reported signs of cell lysis from their SEM examination of microcosm biofilms inoculated from subgingival plaque and treated with CHX 2% for 10 min. In contrast, SEM visualization of a polymicrobial biofilm comprising putative periodontal pathogens A. naeslundii , Fusobacterium nucleatum, and Porphyromonas gingivalis showed no suchlike vesicles, but cellular debris only after treatment with CHX 0.2% for 20 min (Cieplik et al., ). While Vitkov et al.…”

“…Both, CHX and CPC, revealed high percentages of PI‐positive or double‐stained bacterial cells, indicating membrane damage, which is in line with the SEM visualization. Furthermore, in the literature the mechanism of antimicrobial action of CHX and CPC is described as damage of bacterial membranes and subsequent leakage of cytoplasmic constituents (Cieplik et al., ; Jones, ; McDonnell & Russell, ). Citrus extract also led to an increase in PI‐positive cells as compared to the untreated control group and therefore may also target on bacterial membranes, as it is known from other essential oils and flavonoids (Paparella et al., ).…”

Killing mechanism of bacteria within multi-species biofilm by blue light

“…Gram-positive bacteria implicated in periodontitis include oral streptococci of the Mitis group and Actinomyces naeslundii. The streptococci once considered strict commensals in the oral cavity [6,24] do not cause significant pathological changes [6,20,21]. However, mixed infections (for example, with P. gingivalis) may result in increased disease severity [6].…”

“…However, mechanical debridement does not always lead to major clinical improvement which sometimes can be ameliorated considerably by the adjunctive use of antibiotics [24]. Yet, antibiotics have side effects, and when overused may contribute to antibiotic resistance [20,21,[25][26][27]. An alternative antimicrobial approach to the treatment of periodontitis is lethal photosensitization or antimicrobial photodynamic therapy (aPDT).…”

“…However, the use of dyes is associated with two main problems: the inability of the dye to diffuse throughout the biofilm and the compromised esthetic results owing to staining of the oral tissues. Despite the development of stain-free Phenalen-1-one photosensitizers (PS), such agents have not been approved for clinical use [21,34].…”