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.

The photodynamic inactivation (PDI) uses molecules (photosensitizers) that absorb visible light (385-450 nm) energy, transfer it to adjacent molecular oxygen and thereby generating the biocidal singlet oxygen and other reactive oxygen species in situ. Efficacy of PDI was tested against Listeria monocytogenes and Salmonella enterica in three ways. Firstly, by adding the photosensitizer to bacterial suspensions. Secondly, bacteria were placed on inanimate surfaces and then sprayed with a photosensitizer suspension. Thirdly, bacteria were placed on coated inanimate surfaces, where the photosensitizer was permanently fixed in this coating (antimicrobial coating, AMC). Experiments were performed without and with soiling (albumin, sheep erythrocytes). In suspension, PDI reduced the number of viable Listeria monocytogenes and Salmonella enterica by more than 6 Log CFU/mL within seconds of light exposure. Photosensitizer spray suspension reduced the bacterial burden on surfaces with up to about 6 Log CFU/mL (5 s light exposure). PDI, even in the presence of high soiling, achieved a reduction of up to 5.1 +/- 1.2 Log CFU/mL. The AMC showed a bacterial reduction that decreased from 5.1 to 0.7 Log CFU/mL with increasing soiling. Depending on the soiling and the respective bacteria, the spray suspension or AMC achieved a bacterial reduction on the running conveyor belt demonstrator ranging from 2.9 to 5.3 or 0.5 to 4.5 Log CFU/mL, respectively. PDI used visible light, phenalene-1-one and curcumin photosensitizers, and oxygen from ambient air to reduce the bioburden on typical surfaces in food processing. The AMC acts slower than the spray suspension but enables a permanent, self-sanitizing effect.

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.

The photodynamic inactivation (PDI) uses molecules (photosensitizers) that absorb visible light energy, transfer it to adjacent molecular oxygen and thereby generating the biocidal singlet oxygen in situ . PDI was tested against Listeria monocytogenes and Salmonella enterica in suspensions, on inoculated surfaces using spray suspensions and antimicrobial coatings (AMC), without and with soiling. In suspension, PDI reduced the number of viable Listeria monocytogenes and Salmonella enterica with more than 6 log 10 steps within seconds or minutes of light exposure. The use of a photosensitizer spray suspension and five second light exposure reduced the bacterial burden on surfaces with up to about 6 log 10 steps, which was still more than 3 log 10 steps in the presence of high soiling. The AMC showed a bacterial reduction in a range of 0.7 to 5.1 log 10 steps depending on the soiling concentration using 10 minutes light exposure. PDI was also effective on a running conveyor belt demonstrator.PDI uses visible light, harmless photosensitizers and oxygen from ambient air to reduce effectively the bioburden on typical surfaces in food processing. The AMC acts a little slower but enables a permanent, self-sanitizing effect. Noteworthy, PDI is a modality that does not trigger resistance in bacteria.

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.

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

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.

ABSTRACT Many studies show that photodynamic inactivation (PDI) is a powerful tool for the fight against pathogenic, multiresistant bacteria and the closing of hygiene gaps. However, PDI studies have been frequently performed under standardized in vitro conditions comprising artificial laboratory settings. Under real‐life conditions, however, PDI encounters substances like ions, proteins, amino acids and fatty acids, potentially hampering the efficacy of PDI to an unpredictable extent. Thus, we investigated PDI with the phenalene‐1‐one‐based photosensitizer SAPYR against Escherichia coli and Staphylococcus aureus in the presence of calcium or magnesium ions, which are ubiquitous in potential fields of PDI applications like in tap water or on tissue surfaces. The addition of citrate should elucidate the potential as a chelator. The results indicate that PDI is clearly affected by such ubiquitous ions depending on its concentration and the type of bacteria. The application of citrate enhanced PDI, especially for Gram‐negative bacteria at certain ionic concentrations ( e.g. CaCl 2 or MgCl 2 : 7.5 to 75 mmol L −1 ). Citrate also improved PDI efficacy in tap water (especially for Gram‐negative bacteria) and synthetic sweat solution (especially for Gram‐positive bacteria). In conclusion, the use of chelating agents like citrate may facilitate the application of PDI under real‐life conditions.

Photodynamic inactivation (PDI) of pathogenic bacteria is a promising technology in different applications. Thereby, a photosensitizer (PS) absorbs visible light and transfers the energy to oxygen yielding reactive oxygen species (ROS). The produced ROS are then capable of killing microorganisms via oxidative damage of cellular constituents. Among other PS, some flavins are capable of producing ROS and cationic flavins are already successfully applied in PDI. When PDI is used for example on tap water, PS like flavins will encounter various ions and other small organic molecules which might hamper the efficacy of PDI. Thus, the impact of carbonate and phosphate ions on PDI using two different cationic flavins (FLASH-02a, FLASH-06a) was investigated using Staphylococcus aureus and Pseudomonas aeruginosa as model organisms. Both were inactivated in vitro at a low light exposure of 0.72 J cm - 2 . Upon irradiation, FLASH-02a reacts to single substances in the presence of carbonate or phosphate, whereas the photochemical reaction for FLASH-06a was more unspecific. DPBF-assays indicated that carbonate and phosphate ions decreased the generation of singlet oxygen of both flavins. Both microorganisms could be easily inactivated by at least one PS with up to 6 log 10 steps of cell counts in low ion concentrations. Using the constant radiation exposure of 0.72 J cm -2 , the inactivation efficacy decreased somewhat at medium ion concentrations but reached almost zero for high ion concentrations. Depending on the application of PDI, the presence of carbonate and phosphate ions is unavoidable. Only upon light irradiation such ions may attack the PS molecule and reduce the efficacy of PDI. Our results indicate concentrations for carbonate and phosphate, in which PDI can still lead to efficient reduction of bacterial cells when using flavin based PS.

Archaea are considered third, independent domain of living organisms besides eukaryotic and bacterial cells. To date, no report is available of photodynamic inactivation (PDI) of any archaeal cells. Two commercially available photosensitizers (SAPYR and TMPyP) were used to investigate photodynamic inactivation of Halobacterium salinarum. In addition, a novel high-throughput method was tested to evaluate microbial reduction in vitro. Due to the high salt content of the culture medium, the physical and chemical properties of photosensitizers were analyzed via spectroscopy and fluorescence-based DPBF assays. Attachment or uptake of photosensitizers to or in archaeal cells was investigated. The photodynamic inactivation of Halobacterium salinarum was evaluated via growth curve method allowing a high throughput of samples. The presented results indicate that the photodynamic mechanisms are working even in high salt environments. Either photosensitizer inactivated the archaeal cells with a reduction of 99.9% at least. The growth curves provided a fast and precise measurement of cell viability. The results show for the first time that PDI can kill not only bacterial cells but also robust archaea. The novel method for generating high-throughput growth curves provides benefits for future research regarding antimicrobial substances in general.

Background Near-patient surfaces are recognized as a source for hospital-acquired infections. Such surfaces act as reservoirs for microbial contamination by which pathogens can be transmitted from colonized or infected patients to susceptible patients. Routine disinfection of surfaces only results in a temporal elimination of pathogens, and recontamination inevitably occurs shortly between disinfections. Aim A novel antimicrobial coating based on photodynamics was tested under laboratory conditions and subsequently in a field study in two hospitals under real-life conditions. Methods Identical surfaces received a photodynamic or control coating. Bacterial counts [colony-forming units (cfu)/cm2) were assessed regularly for up to 6 months. Findings The laboratory study revealed a mean reduction of several human pathogens of up to 4.0 ± 0.3 log10. The field study in near-patient environments demonstrated mean bacterial values of 6.1 ± 24.7 cfu/cm2 on all control coatings. Photodynamic coatings showed a significantly lower mean value of 1.9 ± 2.8 cfu/cm2 (P<0.001). When considering benchmarks of 2.5 cfu/cm2 or 5 cfu/cm2, the relative risk for high bacterial counts on surfaces was reduced by 48% (odds ratio 0.38, P<0.001) or 67% (odds ratio 0.27, P<0.001), respectively. Conclusion Photodynamic coatings provide a significant and lasting reduction of bacterial counts on near-patient surfaces, particularly for high bacterial loads, in addition to routine hygiene. The promising results of this proof-of-concept study highlight the need for further studies to determine how this novel technology is correlated with the frequency of hospital-acquired infections.

Background To prevent infections that arise from the skin surface it is necessary to decolonize human skin prior to any proposed treatment or surgical intervention. Photodynamic inactivation of bacteria (PIB) uses cationic photosensitizers that attach to the surface of bacteria, generate reactive oxygen species on light irradiation and thereby kill bacteria via oxidative mechanisms. Objectives To evaluate the potential and the safety of PIB for decolonization of bacteria from skin. Methods PIB with the new photosensitizer SAPYR [2-((4-pyridinyl)methyl)-1H-phenalen-1-one chloride] was initially tested against different bacterial species in vitro. Then, ex vivo porcine skin samples were used as a model for decolonization of different bacteria species. The numbers of viable bacteria were quantified and the mitochondrial activity of skin cells was histologically analysed (using nitroblue tetrazolium chloride, NBTC). The same procedure was performed for human skin and meticillin-resistant Staphylococcus aureus (MRSA). Results The in vitro studies showed a 5 log(10) reduction of all tested bacterial species. On ex vivo porcine skin samples, PIB reduced the viability of all tested bacterial species by at least 3 log(10) steps. On human skin samples ex vivo, PIB reduced the number of viable MRSA by maximal 4 center dot 4 log(10) steps (1000 mu mol L-1 SAPYR, incubation time 10 min, 60 J cm(-2)). NBTC staining showed normal mitochondrial activity in skin cells after all PIB modalities. Conclusions The results of this study show that PIB can effectively and safely kill bacteria like MRSA on the skin surface and might have the potential of skin decolonization in vivo.

One of the sources of infections in hospitals is the presence of potentially harmful bacteria on the skin surface (carriage) of a patient without the development of an infection, but which can spread to other people under certain conditions. Bacteria living on the skin surface can also contribute to worsening of eczema. The current methods of ridding the skin of these microbes (bacteria) involves giving the patient either topical (on the skin) or oral (by mouth) antibiotics, a strategy which, over time, is thought to have caused antibiotic resistance, meaning the antibiotics can no longer kill the bacteria. The study described in this paper was carried out by a group from the University of Regensburg in Germany. They used excised pig and human skin samples to which they had added drug resistant bacteria, such as methicillin resistant staphylococci or MRSA, and then treated the skin with a chemical in solution that acts by increasing sensitivity to light. Skin samples were then exposed to a source of light, a process known as photodynamic activation. They found that this technique led to a large reduction in the numbers of bacteria, without damage to skin cells. The authors suggest that this process should now be investigated as a safer method of reducing surface bacterial carriage without increasing the risk of bacterial resistance and without damaging the skin.

作为医院感染的来源之一, 患者皮肤表面(载体)存在潜在有害细菌, 它们不会产生感染, 但在某些条件下可能传播给其他人。皮肤表面生活的细菌也会导致湿疹恶化。目前去除这些微生物(细菌)皮肤的方法包括给患者使用局部抗生素(皮肤上的)或口服抗生素(口服),但随着时间的推移, 这种策略被认为导致了抗生素耐药性, 这意味着抗生素不再能杀死细菌。本文中描述的是由德国雷根斯堡大学的一个小组进行的研究。他们使用切掉的猪和人体皮肤样本, 在样本中加入耐药细菌,如耐甲氧西林葡萄球菌或 MRSA, 然后用一种化学溶液对皮肤进行处理, 这种化学溶液的作用是增加对光的敏感性。皮肤样本随后暴露在光源下,这一过程被称为光动力激活。他们发现这种技术可以在不损害皮肤细胞的情况下, 大量减少细菌的数量。作者建议,这一过程现在应该作为一种更安全的方法来研究, 以减少表面细菌运输, 而不增加细菌耐药性的风险,也不损害皮肤。

Photodynamic inactivation of bacteria (PIB) is based on photosensitizers which absorb light and generate reactive oxygen species (ROS), killing cells via oxidation. PIB is evaluated by comparing viability with and without irradiation, where reduction of viability in the presence of the photosensitizer without irradiation is considered as dark toxicity. This effect is controversially discussed for photosensitizers like TMPyP (5,10,15,20-Tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluensulfonate). TMPyP shows a high absorption coefficient for blue light and a high yield of ROS production, especially singlet oxygen. Escherichia coli and Bacillus atrophaeus were incubated with TMPyP and irradiated with different light sources at low radiant exposures (μW per cm²), reflecting laboratory conditions of dark toxicity evaluation. Inactivation of E. coli occurs for blue light, while no effect was detectable for wavelengths >450 nm. Being more susceptible toward PIB, growth of B. atrophaeus is even reduced for light with emission >450 nm. Decreasing the light intensities to nW per cm² for B. atrophaeus, application of TMPyP still caused bacterial killing. Toxic effects of TMPyP disappeared after addition of histidine, quenching residual ROS. Our experiments demonstrate that the evaluation of dark toxicity of a powerful photosensitizer like TMPyP requires low light intensities and if necessary additional application of substances quenching any residual ROS.