Antimicrobial photodynamic therapy – what we know and what we don’t

Abstract

Considering increasing number of pathogens resistant towards commonly used antibiotics as well as antiseptics, there is a pressing need for antimicrobial approaches that are capable of inactivating pathogens efficiently without the risk of inducing resistances. In this regard, an alternative approach is the antimicrobial photodynamic therapy (aPDT). The antimicrobial effect of aPDT is based on the principle that visible light activates a per se non-toxic molecule, the so-called photosensitizer (PS), resulting in generation of reactive oxygen species that kill bacteria unselectively via an oxidative burst. During the last 10-20 years, there has been extensive in vitro research on novel PS as well as light sources, which is now to be translated into clinics. In this review, we aim to provide an overview about the history of aPDT, its fundamental photochemical and photophysical mechanisms as well as photosensitizers and light sources that are currently applied for aPDT in vitro. Furthermore, the potential of resistances towards aPDT is extensively discussed and implications for proper comparison of in vitro studies regarding aPDT as well as for potential application fields in clinical practice are given. Overall, this review shall provide an outlook on future research directions needed for successful translation of promising in vitro results in aPDT towards clinical practice.

Nanomedicine Fight against Antibacterial Resistance: An Overview of the Recent Pharmaceutical Innovations

“…The unique advantage of this technique over other conventional ones is the dual selectivity behavior. The photosensitizer only accumulates in the rapidly growing bacterial cells and application of light leads to the photo-destructive effect limited to the area where the light is delivered, criteria that prevent the recurrence of infection [194]. Sanjana Ghosh et al [195] investigated the loading of ciprofloxacin into photoactivatable liposomes that were made of porphyrin-phospholipid.…”

Application of Teeth Whitening LED for Prevention of Dental Caries : Antimicrobial Photodynamic Therapy Approach

“…Photoactivated reactive oxygen species (singlet oxygen and toxic radicals) begin oxidizing organic molecules, resulting in localized photodamage and death of microorganisms [6]. In dentistry, aPDT has been proven to be very effective in the reduction of microbial load in the oral biofilms on teeth and soft tissue surfaces [7][8][9]. Therefore, aPDT can be a useful tool for controlling biofilms and preventing the risk of caries.…”

Metal Complexes, an Untapped Source of Antibiotic Potential?

“…The propensity of these complexes to bind DNA/RNA makes these likely targets for this class of ruthenium compounds. The potential for aPDT is particularly promising for localized infections, where conventionally a systemic antibiotic would be administered [75]. Traditional targets include skin and wound infections but thanks to advances in endoscopes and fiber optic devices, most body areas e.g., ear, nose oral cavity, gastrointestinal tract, urogenital tract, and lungs are now accessible to localized light irradiation for aPDT [76].…”

“…Since the ROS generated in aPDT treatments has many possible targets, it is difficult for bacteria to develop resistance mechanisms against this therapy. Indeed, no conclusive evidence of resistance against aPDT has been reported to date [75,77]. In general, further work is required to probe the capability of bacteria to develop resistance against metal complex-based treatments.…”