Violet 405 nm light: A novel therapeutic agent against β-lactam-resistant Escherichia coli

Hospital, Catheter, Peritoneal Dialysis Acquired Infections: Visible Light as a New Solution to Reduce Risk and Incidence

Healthcare-associated infections, often identified as hospital-acquired infections (HAIs), are typically not present during patient contact or admission. Healthcare-associated infections cause longer lengths of stay, increasing costs and mortality. HAI occurring in trauma patients increases the risk for length of stay and higher inpatient costs. Many HAIs are preventable. Antibiotic resistance has increased to a high level making proper treatment increasingly difficult due to organisms resistant to common antibiotics. Therefore, there is a need for alternate forms of attack against these pathogens. Currently, the application of light for the treatment of topical infections has been used. Ultraviolet (UV) light has well-documented antimicrobial properties. UV is damaging to DNA and causes the degradation of plastics, etc., so its use for medical purposes is limited. Using visible light may be more promising. 405-nm light sterilization has been shown to be highly efficacious in reducing bacteria. Light Line Medical, Inc.'s (LLM) patented visible-light platform technology for infection prevention may create a global shift in the prevention of healthcare-associated infections. LLM has developed a proprietary method of delivering light to prevent catheter-associated infections. This technology uses non-UV visible light and can kill both bacteria and prevent biofilm inside and outside a luminal catheter. This is significant as prevention is key. Independent analysis of the prototype system showed the application of the device met the acceptance criterion of 4 x 109-10 reduction in Candida albicans, Staphylococcus aureus, Pseudomonas aeruginosa, and other bacteria and fungal species. Further design evolution for this technology continues, and the FDA submission process is underway.

Phototherapy of Pseudomonas aeruginosa-Infected Wounds: Preclinical Evaluation of Antimicrobial Blue Light (450-460 nm) Using In Vitro Assays and a Human Wound Skin Model

Objective: To determine effective treatment strategies against bacterial infections of burn wounds with Pseudomonas aeruginosa, we tested different treatment regimens with antibacterial blue light (BL). Background: Infections of burn wounds are serious complications and require effective and pathogen-specific therapy. Hereby, infections caused by P. aeruginosa pose a particular challenge in clinical practice due to its resistance to many antibiotics and topical antiseptics. Methods: LED-based light sources (450-460 nm) with different intensities and treatment times were used. Antibacterial effects against P. aeruginosa were determined by colony-forming unit (CFU) assays, human skin wound models, and fluorescence imaging. Results: In suspension assays, BL (2 h, 40 mW/cm², 288 J/cm²) reduced bacterial number (>5 log₁₀ CFU/mL). Applying 144 J/cm², using 40 mW/cm² for 1 h was more effective (>4 log₁₀ CFU) than using 20 mW/cm² for 2 h (>1.5 log₁₀ CFU). BL with low irradiance (24 h, 3.5 mW/cm², 300 J/cm²) only revealed bacterial reduction in thin bacteria-containing medium layers. In infected in vitro skin wounds only BL irradiation (2 h, 40 mW/cm², 288 J/cm²) exerted a significant antimicrobial efficacy (2.94 log₁₀ CFU/mL). Conclusions: BL treatment may be an effective therapy for P. aeruginosa-infected wounds to avoid radical surgical debridement. However, a significant antibacterial efficacy can only be achieved with higher irradiances and longer treatment times (min. 40 mW/cm²; >1 h), which cannot be easily integrated into regular clinical treatment protocols, for example, during a dressing change. Further studies are necessary to establish BL therapy for infected burns among tissue compatibility and interactions with previous therapeutic agents.

Cavity Disinfection With a 445 nm Diode Laser Within the Scope of Restorative Therapy - A Pilot Study

Introduction: Cavity disinfection is necessary to prevent a progressive infection of the crown dentin and pulp. Increasing intolerance and resistance to antiseptics and antibiotics as well as the controversy over the effects of those on the dental hard tissue and composite have prompted the investigation of alternative treatment options. The objective of this pilot study is to evaluate the antibacterial potential of a diode laser with a wavelength of 445 nm in the cavity preparation using the bacterium Streptococcus salivarius associated with caries in conjunction with the characteristics and influences of dentin on light transmission. Methods: The bactericidal effect of the laser irradiation was determined in culture experiments by using caries-free human dentin samples on bacteria-inoculated agar. For this, dentin discs (horizontally cut coronal dentin) of 500 µm and 1000 µm thicknesses were produced and irradiated with the laser with irradiation parameters of 0.7-1 W in a cw-mode and exposure times of between 5-30 s. Based on the different sample thicknesses, the penetration depth effect of the irradiation was ascertained after the subsequent incubation of the bacteria-inoculated agar. Additional influential parameters on the irradiation transmission were investigated, including surface moisture, tooth color as well as the presence of a smear layer on the dentin surface. Results: The optical transmission values of the laser radiation for dentin were significantly dependent on the sample thickness (P = 0.006) as well as its moisture content (P = 0.013) and were independent of the presence of a smear layer. There was a 40% reduction in bacteria after the radiography of the 500-µm-thick dentin samples, which was shown as the lowest laser dose (443 J/cm²). Conclusion: These findings indicate that the diode laser with light emission at a wavelength of 445 nm is interesting for the supportive cavity disinfection within the scope of caries therapy and show potential for clinical applications.

Trends, Epidemiology, and Management of Multi-Drug Resistant Gram-Negative Bacterial Infections in the Hospitalized Setting

The increasing prevalence of antibiotic resistance is a threat to human health, particularly within vulnerable populations in the hospital and acute care settings. This leads to increasing healthcare costs, morbidity, and mortality. Bacteria rapidly evolve novel mechanisms of resistance and methods of antimicrobial evasion. Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii have all been identified as pathogens with particularly high rates of resistance to antibiotics, resulting in a reducing pool of available treatments for these organisms. Effectively combating this issue requires both preventative and reactive measures. Reducing the spread of resistant pathogens, as well as reducing the rate of evolution of resistance is complex. Such a task requires a more judicious use of antibiotics through a better understanding of infection epidemiology, resistance patterns, and guidelines for treatment. These goals can best be achieved through the implementation of antimicrobial stewardship programs and the development and introduction of new drugs capable of eradicating multi-drug resistant Gram-negative pathogens (MDR GNB). The purpose of this article is to review current trends in MDR Gram-negative bacterial infections in the hospitalized setting, as well as current guidelines for management. Finally, new and emerging antimicrobials, as well as future considerations for combating antibiotic resistance on a global scale are discussed.

Antimicrobial blue light for decontamination of platelets during storage

Platelet (PLT) storage is currently limited to 5 days in clinics in the United States, in part, due to an increasing risk for microbial contamination over time. In light of well-documented antimicrobial activity of blue light (405-470 nm), we investigated potentials to decontaminate microbes during PLT storage by antimicrobial blue light (aBL). We found that PLTs produced no detectable levels of porphyrins or their derivatives, the chromophores that specifically absorb blue light, in marked contrast to microbes that generated porphyrins abundantly. The difference formed a basis with which aBL selectively inactivated contaminated microbes prior to and during the storage, without incurring any harm to PLTs. In accordance with this, when contamination with representative microbes was simulated in PLT concentrates supplemented with 65% of PLT additive solution in a standard storage bag, all "contaminated" microbes tested were completely inactivated after exposure of the bag to 405 nm aBL at 75 J/cm2 only once. While killing microbes efficiently, this dose of aBL irradiation exerted no adverse effects on the viability, activation or aggregation of PLTs ex vivo and could be used repeatedly during PLT storage. PLT survival in vivo was also unaltered by aBL irradiation after infusion of aBL-irradiated mouse PLTs into mice. The study provides proof-of-concept evidence for a potential of aBL to decontaminate PLTs during storage.

Can light-based approaches overcome antimicrobial resistance?

The relentless rise of antibiotic resistance is considered one of the most serious problems facing mankind. This mini-review will cover three cutting-edge approaches that use light-based techniques to kill antibiotic-resistant microbial species, and treat localized infections. First, we will discuss antimicrobial photodynamic inactivation using rationally designed photosensitizes combined with visible light, with the added possibility of strong potentiation by inorganic salts such as potassium iodide. Second, the use of blue and violet light alone that activates endogenous photoactive porphyrins within the microbial cells. Third, it is used for "safe UVC" at wavelengths between 200 nm and 230 nm that can kill microbial cells without damaging host mammalian cells. We have gained evidence that all these approaches can kill multidrug resistant bacteria in vitro, and they do not induce themselves any resistance, and moreover can treat animal models of localized infections caused by resistant species that can be monitored by noninvasive bioluminescence imaging. Light-based antimicrobial approaches are becoming a growing translational part of anti-infective treatments in the current age of resistance.

Porphyrins and flavins as endogenous acceptors of optical radiation of blue spectral region determining photoinactivation of microbial cells

It is shown that exposure of suspensions of gram-positive Staphylococcus aureus, gram-negative Escherichia coli and yeast-like fungi Candida albicans to laser radiation of blue spectral region with 405 and 445 nm causes their growth inhibition without prior addition of exogenous photosensitizers. It is experimentally confirmed that compounds of flavin type capable of sensitizing the formation of reactive oxygen species can act as acceptors of optical radiation of blue spectral region determining its antimicrobial effect along with endogenous metal-free porphyrins (the role of endogenous porphyrins has been confirmed earlier by a number of researchers). The participation of these compounds in the antimicrobial effect of laser radiation is supported by the registration of porphyrin and flavin fluorescence in extracts of microbial cells upon excitation by radiation used to inactivate the pathogens. In addition, the intensity of the porphyrin fluorescence in extracts of microbial cells in the transition from radiation with λ = 405 nm to radiation with λ = 445 nm decreases by 15-30 times, whereas the photosensitivity of the cells under study in this transition decreases only 3.7-6.2 times. The contribution of porphyrin photosensitizers is most pronounced upon exposure to radiation with λ = 405 nm (absorption maximum of the Soret band of porphyrins), and flavins - upon exposure to radiation with λ = 445 nm (maximum in the flavin absorption spectrum and minimum in the absorption spectrum of porphyrins). The ratio between the intensity of the porphyrin and flavin components in the fluorescence spectrum of extracts depends on the type of microbial cells.

Antimicrobial blue light inactivation of pathogenic microbes: State of the art

As an innovative non-antibiotic approach, antimicrobial blue light in the spectrum of 400-470nm has demonstrated its intrinsic antimicrobial properties resulting from the presence of endogenous photosensitizing chromophores in pathogenic microbes and, subsequently, its promise as a counteracter of antibiotic resistance. Since we published our last review of antimicrobial blue light in 2012, there have been a substantial number of new studies reported in this area. Here we provide an updated overview of the findings from the new studies over the past 5 years, including the efficacy of antimicrobial blue light inactivation of different microbes, its mechanism of action, synergism of antimicrobial blue light with other angents, its effect on host cells and tissues, the potential development of resistance to antimicrobial blue light by microbes, and a novel interstitial delivery approach of antimicrobial blue light. The potential new applications of antimicrobial blue light are also discussed.

Photoinactivation of bacteria by endogenous photosensitizers and exposure to visible light of different wavelengths - a review on existing data

Visible light has strong disinfectant properties, a fact that is not well known in comparison to the antibacterial properties of UV light. This review compiles the published data on bacterial inactivation caused by visible light and endogenous photosensitizers. It evaluates more than 50 published studies containing information on about 40 different bacterial species irradiated within the spectral range from 380 to 780 nm. In the available data a high variability of photoinactivation sensitivity is observed, which may be caused by undefined illumination conditions. Under aerobic conditions almost all bacteria except spores should be reduced by at least three log-levels with a dose of about 500 J cm^-2 of 405 nm irradiation, including both Gram-positive as well as Gram-negative microorganisms. Irradiation of 470 nm is also appropriate for photoinactivating all bacteria species investigated so far but compared to 405 nm illumination it is less effective by a factor between 2 and 5. The spectral dependence of the observed photoinactivation sensitivities gives reason to the assumption that a so far unknown photosensitizer may be involved at 470 nm photoinactivation.