Millions of people use public transportation daily worldwide and frequently touch surfaces, thereby producing a reservoir of microorganisms on surfaces increasing the risk of transmission. Constant occupation makes sufficient cleaning difficult to achieve. Thus, an autonomous, permanent, antimicrobial coating (AMC) could keep down the microbial burden on such surfaces. A photodynamic AMC was applied to frequently touched surfaces in buses. The microbial burden (colony forming units, cfu) was determined weekly and compared to equivalent surfaces in buses without AMC (references). The microbial burden ranged from 0–209 cfu/cm2 on references and from 0–54 cfu/cm2 on AMC. The means were 13.4 ± 29.6 cfu/cm2 on references and 4.5 ± 8.4 cfu/cm2 on AMC (p < 0.001). The difference in microbial burden on AMC and references was almost constant throughout the study. Considering a hygiene benchmark of 5 cfu/cm2, the data yield an absolute risk reduction of 22.6% and a relative risk reduction of 50.7%. In conclusion, photodynamic AMC kept down the microbial burden, reducing the risk of transmission of microorganisms. AMC permanently and autonomously contributes to hygienic conditions on surfaces in public transportation. Photodynamic AMC therefore are suitable for reducing the microbial load and closing hygiene gaps in public transportation.

No 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.

No abstract

Background The colonization of skin with pathogenic, partially antibiotic‐resistant bacteria is frequently a severe problem in dermatological therapies. For instance, skin colonization with Staphylococcus aureus is even a disease‐promoting factor in atopic dermatitis. The photodynamic inactivation (PDI) of bacteria could be a new antibacterial procedure. Upon irradiation with visible light, a special photosensitizer exclusively generates singlet oxygen. This reactive oxygen species kills bacteria via oxidation independent of species or strain and their antibiotic resistance profile causing no bacterial resistance on its part. Objective To investigate the antibacterial potential of a photosensitizer, formulated in a new hydrogel, on human skin ex vivo. Methods The photochemical stability of the photosensitizer and its ability to generate singlet oxygen in the hydrogel was studied. Antimicrobial efficacy of this hydrogel was tested step by step, firstly on inanimate surfaces and then on human skin ex vivo against S. aureus and Pseudomonas aeruginosa using standard colony counting. NBTC staining and TUNEL assays were performed on skin biopsies to investigate potential necrosis and apoptosis effects in skin cells possibly caused by PDI. Results None of the hydrogel components affected the photochemical stability and the life time of singlet oxygen. On inanimate surfaces as well as on the human skin, the number of viable bacteria was reduced by up to 4.8 log10 being more effective than most other antibacterial topical agents. Histology and assays showed that PDI against bacteria on the skin surface caused no harmful effects on the underlying skin cells. Conclusion Photodynamic inactivation hydrogel proved to be effective for decolonization of human skin including the potential to act against superficial skin infections. Being a water‐based formulation, the hydrogel should be also suitable for the mucosa. The results of the present ex vivo study form a good basis for conducting clinical studies in vivo.