Antimicrobial Photodynamic Coatings Reduce the Microbial Burden on Environmental Surfaces in Public Transportation—A Field Study in Buses

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

Photodynamic inactivation of different pathogenic bacteria on human skin using a novel photosensitizer hydrogel

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

Inhibitory effects of calcium or magnesium ions on PDI

Photodynamic inactivation of microorganisms (PDI) finds use in a variety of applications. Several studies report on substances enhancing or inhibiting PDI. In this study, we analyzed the inhibitory potential of ubiquitous salts like CaCl2 and MgCl2 on PDI against Staphylococcus aureus and Pseudomonas aeruginosa cells using five cationic photosensitizers methylene blue, TMPyP, SAPYR, FLASH-02a and FLASH-06a. TMPyP changed its molecular structure when exposed to MgCl2, most likely due to complexation. CaCl2 substantially affected singlet oxygen generation by MB at small concentrations. Elevated concentrations of CaCl2 and MgCl2 impaired PDI up to a total loss of bacterial reduction, whereas CaCl2 is more detrimental for PDI than MgCl2. Binding assays cannot not explain the differences of PDI efficacy. It is assumed that divalent ions tightly bind to bacterial cells hindering close binding of the photosensitizers to the membranes. Consequently, photosensitizer binding might be shifted to outer compartments like teichoic acids in Gram-positives or outer sugar moieties of the LPS in Gram-negatives, attenuating the oxidative damage of susceptible cellular structures. In conclusion, CaCl2 and MgCl2 have an inhibitory potential at different phases in PDI. These effects should be considered when using PDI in an environment that contains such salts like in tap water or different fields of food industry

Photodynamic inactivation of different pathogenic bacteria on human skin using a novel photosensitizer hydrogel

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.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe