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Background The persistence of infectious organisms on hospital surfaces presents a significant challenge to healthcare environments. Low irradiance visible 405-nm light has recently been developed as a method for environmental decontamination, with studies demonstrating successful reductions of environmental bacteria in wards and operating theatres. This study investigates the antimicrobial efficacy of 405-nm light for decontamination of surfaces, and how the dose-response kinetics are affected by use of differing light irradiances. Methods Surface-seeded Staphylococcus aureus and Pseudomonas aeruginosa (selected as model Gram-positive and Gram-negative species) were exposed to increasing doses of 405-nm light (≤ 90 Jcm-2) at three discrete irradiances (0.5, 5 and 50 mWcm-2). For both species, inactivation kinetics at each respective irradiance was established and susceptibility at equivalent light doses compared. Results Results demonstrate increased bacterial susceptibility to 405-nm light inactivation when exposed at lower irradiance treatments. For both species, 3 Jcm-2 was required when exposed using 0.5 mWcm-2 irradiance to achieve significant bacterial inactivation (P < 0.05; 26.7-73.7% reduction). When exposed at 5 mWcm-2, double the energy (6 Jcm-2) was required to achieve similar reductions. Exposure at the highest irradiance (50 mWcm-2) required 3-5 times greater dose (9-15 Jcm-2) to achieve similar reductions to the lowest irradiance tested (0.5 mWcm-2). Conclusion This study provides evidence of the enhanced germicidal efficiency of low irradiance 405-nm light, highlighting its efficacy for continuous environmental decontamination applications. Further investigation into the photo-chemical inactivation mechanisms will be crucial for its optimisation for a range of infection control applications.

The introduction of risk prevention measures, such as blood screening and donor deferrals have dramatically reduced the incidence of transfusion-transmitted viral infections. Nevertheless, bacterial contamination of blood transfusion products remains a concern to patient health, and a range of pathogen reduction technologies have been developed to reduce this risk. Visible violet-blue light, in the region of 405-nm, has recently demonstrated potential for in situ treatment of ex vivo stored plasma and platelet products, without the need for additional photosensitizers. This study assessed the broad-spectrum efficacy of 405-nm light against a range of bacteria implicated in transfusion-transmitted infections: Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniaeandYersinia enterocolitica. Plasma was seeded with clinically-relevant low-level bacterial contamination (102-103CFUmL-1) and exposed to a 405-nm light dose of 360 Jcm-2 (1-hr at 100mWcm-2) using a small-scale exposure system. Broad spectrum antibacterial efficacy was observed, with 99.0 – 100% inactivation achieved for all bacterial species tested. Bacterial inactivation tests were then scaled-up to expose large volumes of prebagged plasma seeded with S. aureusat ~103 CFUmL-1, to 22mWcm-2 405-nm light, under agitation, (≤396 Jcm-2). Successful bacterial inactivation was observed using the large-scale exposure system, with a dose of 238 Jcm-2 (3-hr at ~22mWcm-2) achieving complete (3.5-log10) reductions in prebagged bacterial-seeded plasma (P=0.001). Results from this study support further development of visible 405-nm light technology as a bactericidal tool for application in transfusion medicine. This abstract reflects the views of the author and should not be construed to represent FDA’s views or policies.

Transfusion-related sepsis is the most frequent infectious complication of blood transfusion. With millions of units transfused per year, product safety is key to public health but currently relies upon donor deferral and product testing. Pathogen reduction technologies can also be used, with several systems CE marked or FDA approved for platelet and plasma use, but only one CE marked for whole blood. 405 nm violet-blue light has recently demonstrated potential for in situ bacterial reduction of ex vivo stored plasma and platelet products, along with preliminary antiviral potential in plasma. This study assesses the potential compatibility of 405 nm antimicrobial light with red blood cell (RBC) components. Sheep RBC were analysed, showing light transmissibility and absorption characteristics over wavelengths of 220-1100 nm using neat–1000X dilutions. Irradiances of 10-100 mW/cm2 405 nm light were then applied to red cell samples with ∼1.3 & 7.8 mm depths over 10-60 minutes, giving doses of 9-360 J/cm2. Treatment effects on cell integrity were demonstrated by microscopy and photometric detection of leaked haemoglobin using the Harboe method. RBC transmission analysis highlighted the high opacity of RBC suspension at 18% haematocrit with 1 cm depths, with peak absorption found to be at 417 nm. Results suggested the requirement of sample depths

Microbial surface attachment negatively impacts a wide range of devices from water purification membranes to biomedical implants. Mimics of antimicrobial peptides (AMPs) constituted from poly(N-substituted glycine) "peptoids" are of great interest as they resist proteolysis and can inhibit a wide spectrum of microbes. We investigate how terminal modification of a peptoid AMP-mimic and its surface immobilization affect antimicrobial activity. We also demonstrate a convenient surface modification strategy for enabling alkyne-azide "click" coupling on amino-functionalized surfaces. Our results verified that the N- and C-terminal peptoid structures are not required for antimicrobial activity. Moreover, our peptoid immobilization density and choice of PEG tether resulted in a "volumetric" spatial separation between AMPs that, compared to past studies, enabled the highest AMP surface activity relative to bacterial attachment. Our analysis suggests the importance of spatial flexibility for membrane activity and that AMP separation may be a controlling parameter for optimizing surface anti-biofouling.

Airborne transmission of infectious organisms is a major public health concern, particularly within healthcare and communal public environments. Methods of environmental decontamination utilising pulsed ultraviolet (UV) light are currently available, however it is important that germicidal efficacy against airborne contamination is established. This study demonstrates evidence of the dose-response kinetics of airborne bacterial contamination when exposed to pulsed UV-rich (PUV) light. Bacterial aerosols (Staphylococcus epidermidis) were generated using a 6-Jet Collison nebuliser, and introduced into a custom-designed aerosol chamber which enabled prolonged airborne suspension and circulation. Bacterial aerosols were exposed to short duration pulses (~20 µs) of UV-rich light emitted from a xenon-filled flashlamp. The lamp was operated using a 1 kV solid–state pulsed power source, with a pulse frequency of 1 Hz, and output energy of 20 J/pulse. Post-treatment, air samples were extracted from the chamber using a BioSampler liquid impinger, and the surviving fraction was enumerated using standard microbiological culture methods. Results demonstrate successful aerosol inactivation, with a 66.4% reduction achieved with only 10 pulses of UV-rich light (P=

Airborne transmission of infectious organisms is a major concern within the healthcare environment. A number of methods for 'whole room' decontamination, such as antimicrobial 405nm light, are being developed, and it is important that efficacy against airborne, as well as surface-deposited contamination is established. This study demonstrates evidence of the dose-response kinetics of airborne bacterial contamination when exposed to 405nm light. Aerosols of Staphylococcus epidermids, generated using a 6-Jet Collison nebuliser, were introduced into an aerosol chamber designed to maintain prolonged airborne suspension and circulation. Aerosolized bacteria were exposed to increasing doses of 405nm light, and air samples were extracted from the chamber using a BioSampler liquid impinger, with viability analysed using pour plate culture. Initial results have demonstrated successful aerosol inactivation, with a 98.4% reduction (1.8 log10 reduction) achieved with 1-hour exposure to low irradiance 405nm light (P=

Objective: This study investigates possible advantages in pulsed over continuous 405-nm LED-light for bacterial inactivation and energy efficiency. Background: Alternative non-antibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm light-emitting diodes for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds. Methods: Liquid suspensions of 103 CFU/ml populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles and intensities, and for different lengths of time. Results: Pulsed exposures with the same average irradiance of 16 mWcm2 and varying duty cycle (25%, 50%, 75%), showed very similar performance compared with continuous exposures, with 95-98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz - 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency. Conclusions: These results suggest that under pulsed conditions a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection-control applications without compromising antimicrobial efficacy.

Pulsed electric fields (PEF) can cause irreversible damage to bio-membranes and may result in inactivation of microorganisms. The aim of this paper is to investigate the PEF treatment of the yeast Saccharomyces cerevisiae, using a novel treatment cell with parallel-plane electrodes coated with a 2 µm thin TiO2 film. Two different PEF waveforms, square and exponential, with magnitudes of 67 kV/cm and 80 kV/cm, were used in this study. The efficacy of the PEF treatment was assessed by comparison of the surviving treated and untreated yeast populations, and it was shown that a treatment cell with TiO2-coated electrodes can be successfully used for the PEF treatment of microorganisms: 3-log10 reduction in the yeast population was achieved with 100 impulses. The energy efficacy of the PEF process in the proposed treatment cell has been compared with the energy losses in the PEF treatment cell with uncoated, conductive electrodes. It is shown that the electrodes coated with TiO2 provide better performance as compared with the traditional uncoated electrodes.

The ability of C. difficile to form spores which can survive for prolonged periods causes significant environmental contamination problems. 405nm light has wide antimicrobial activity against vegetative bacteria, and is being developed for environmental decontamination within hospitals. As expected, spores are more resilient to inactivation. This study aims to establish whether spore susceptibility can be enhanced by combining 405nm light with low concentration chlorinated disinfectants: sodium hypochlorite, Actichlor and Tristel. Spore suspensions were seeded onto surfaces including PVC, stainless steel and vinyl flooring. Disinfectant was added to the surface, and the samples were then exposed to 405nm light at irradiances of ~0.2-225 mWcm-2. Control samples were exposed to 405nm light alone, and disinfectants alone, to establish the sporicidal activity of each agent, and to demonstrate the synergistic effect when combined. Results demonstrated increased sporicidal activity of 405nm light and low-concentration sodium hypochlorite and Actichlor against C. difficile seeded on vinyl flooring and PVC surfaces, with approximately 3-log10 reductions achieved with up to 66% lower doses than achieved with light alone. Tristel demonstrated limited synergy on vinyl and PVC, whilst all three disinfectants demonstrated minimal synergy on stainless steel. Results are also reported for lower intensity light, as used in the clinical environment. In conclusion, the sporicidal efficacy of 405nm light is enhanced when used alongside chlorinated disinfectants. Further research could potentially lead to the use of lower strength chlorinated disinfectants in combination with 405nm light to provide enhanced decontamination of C. difficile spores in the clinical environment.

The ability of Clostridium difficile to form highly resilient spores which can survive in the environment for prolonged periods causes major contamination problems. Antimicrobial 405 nm light is being developed for environmental decontamination within hospitals, however further information relating to its sporicidal efficacy is required. This study aims to establish the efficacy of 405 nm light for inactivation of C. difficile vegetative cells and spores, and to establish whether spore susceptibility can be enhanced by the combined use of 405 nm light with low concentration chlorinated disinfectants. Vegetative cells and spore suspensions were exposed to increasing doses of 405 nm light (at 70–225 mW/cm2) to establish sensitivity. A 99.9% reduction in vegetative cell population was demonstrated with a dose of 252 J/cm2, however spores demonstrated higher resilience, with a 10-fold increase in required dose. Exposures were repeated with spores suspended in the hospital disinfectants sodium hypochlorite, Actichlor and Tristel at non-lethal concentrations (0.1%, 0.001% and 0.0001%, respectively). Enhanced sporicidal activity was achieved when spores were exposed to 405 nm light in the presence of the disinfectants, with a 99.9% reduction achieved following exposure to 33% less light dose than required when exposed to 405 nm light alone. In conclusion, C. difficile vegetative cells and spores can be successfully inactivated using 405 nm light, the sporicidal efficacy can be significantly enhanced when exposed in the presence of low concentration chlorinated disinfectants. Further research may lead to the potential use of 405 nm light decontamination in combination with selected hospital disinfectants to enhance C. difficile cleaning and infection control procedures.

Infection rates following orthopaedic arthroplasty surgery are as high as 4%, while the infection rates are even higher after revision surgery. The duration of routine arthroplasty surgeries is typically between 1 and 2 hours. 405nm High-Intensity Narrow-Spectrum Light (HINS-light) has bactericidal activity against Hospital Acquired Infection (HAI) related bacterial pathogens including MRSA and hence may aid in reducing the incidence of infections that arise from environmental contamination during arthroplasty surgery.

Exposure to narrowband violet-blue light around 405 nm wavelength can induce lethal oxidative damage to bacteria and fungi, however effects on viruses are unknown. As photosensitive porphyrin molecules are involved in the microbicidal inactivation mechanism, and since porphyrins are absent in viruses, then any damaging effects of 405 nm light on viruses might appear unlikely. This study used the bacteriophage ɸC31, as a surrogate for non-enveloped double-stranded DNA viruses, to establish whether 405 nm light can induce virucidal effects. Exposure of ɸC31 suspended in minimal media, nutrient-rich media, and porphyrin solution, demonstrated differing sensitivity of the phage. Significant reductions in phage titer occurred when exposed in nutrient-rich media, with ~3-, 5- and 7-log10 reductions achieved after exposure to doses of 0.3, 0.5 and 1.4 kJ/cm2, respectively. When suspended in minimal media a 0.3-log10 reduction (P = 0.012) occurred after exposure to 306 J/cm2: much lower than the 2.7- and > 2.5-log10 reductions achieved with the same dose in nutrient-rich, and porphyrin-supplemented media, suggesting inactivation is accelerated by the photo-activation of light-sensitive components in the media. This study provides the first evidence of the interaction of narrowband 405 nm light with viruses, and demonstrates that viral susceptibility to 405 nm light can be significantly enhanced by involvement of exogenous photosensitive components. The reduced susceptibility of viruses in minimal media, compared with that of other microorganisms, provides further evidence that the antimicrobial action of 405 nm light is predominantly due to the photo-excitation of endogenous photosensitive molecules such as porphyrins within susceptible microorganisms.

This poster discusses using 405nm HINS-light to make Clostridium difficile cells and spores inactive.

A significant portion of medical devices fail due to acquired infection, with infection rates after arthroplasty surgery between 1-4%, and considerably higher after revision surgery. To reduce the associated costs of infection, a new preventative method is required. High intensity narrow spectrum (HINS) 405 nm light is a new technology shown to have bactericidal effects on a range of medically important bacteria[1]. The effect of HINS-light on osteoblasts and bacteria were investigated to determine the potential of this technology to contribute to infection prevention in operating theatres, during surgery and postoperative dressing changes.