Photodynamic inactivation of pathogenic bacteria on human skin by applying a potent photosensitizer in a hydrogel

Abstract

The antibiotic crisis increasingly threatens the health systems world-wide. Especially as there is an innovation gap in the development of novel antibiotics, treatment options for bacterial infections become fewer. The photodynamic inactivation (PDI) of bacteria appears to be a potent, new technology that may support the treatment of colonized or infected skin. In photodynamic inactivation, a dye - called photosensitizer - absorbs light and generates reactive singlet oxygen. This singlet oxygen is then capable of killing bacteria independent of species or strain and their antibiotic resistance profile. In order to provide a practical application for the skin surface, the photosensitizer was included in an aqueous hydrogel (photodynamically active hydrogel). The efficacy of this gel was initially tested on an inanimate surface and then on the human skin ex vivo. NBTC staining and TUNEL assays were carried out on skin biopsies to investigate potential harmful effects of the surface PDI to the underlying skin cells. The photosensitizer in the gel sufficiently produced singlet oxygen while showing only little photobleaching. On inanimate surfaces as well as on the human skin, the number of viable bacteria was reduced by over or nearly up to 4 log10 steps, equal to 99.99% reduction or even more. Furthermore, histological staining showed no harmful effects of the gel towards the tissue. The application of this hydrogel represents a valuable method in decolonizing human skin including the potential to act against superficial skin infections. The presented results are promising and should lead to further investigation in a clinical study to check the effectivity of the photodynamically active hydrogel on patients.

Photosensitizer‐loaded hydrogels: A new antibacterial dressing

“…In addition, its effectiveness and safety have been demonstrated on infected pig ear skin 28 . Research also shows that these PS‐loaded hydrogels eliminate in vitro 99% of viable bacteria in human abdominal skin 28 . Thus, PS‐loaded hydrogels offer significant therapeutic effects and security in treating bacteria‐infected wounds both under both in vitro and in vivo conditions.…”

“…In vitro experiments ascribed the antibacterial activity mainly to the appropriate ROS production and photostability under visible light 27 . In addition, its effectiveness and safety have been demonstrated on infected pig ear skin 28 . Research also shows that these PS‐loaded hydrogels eliminate in vitro 99% of viable bacteria in human abdominal skin 28 .…”

“…26 Further research measured the antibacterial efficacy of PS-loaded hydrogels in in vitro infection models. 27,28 In 2009, PSs such as methylene blue and porphyrin derivatives were loaded into crosslinked polyvinyl alcohol hydrogels to produce PS-loaded hydrogels with powerful antibacterial activity against methicillinresistant S. aureus. In vitro experiments ascribed the antibacterial activity mainly to the appropriate ROS production and photostability under visible light.…”

“…In vivo experiments have shown that the application of such PS‐loaded hydrogels significantly reduces the bacterial survival rate in infected wounds 26 . Further research measured the antibacterial efficacy of PS‐loaded hydrogels in in vitro infection models 27,28 . In 2009, PSs such as methylene blue and porphyrin derivatives were loaded into crosslinked polyvinyl alcohol hydrogels to produce PS‐loaded hydrogels with powerful antibacterial activity against methicillin‐resistant S. aureus .…”