Photodynamic disinfection of SARS-CoV-2 clinical samples using a methylene blue formulation.

The amplitude of the coronavirus disease 2019 (COVID-19) pandemic motivated global efforts to find therapeutics that avert severe forms of this illness. The urgency of the medical needs privileged repositioning of approved medicines. Methylene blue (MB) has been in clinical use for a century and proved especially useful as a photosensitizer for photodynamic disinfection (PDI). We describe the use of MB to photo-inactivate SARS-CoV-2 in samples collected from COVID-19 patients. One minute of treatment can reduce the percentage inhibition of amplification by 99.99% under conditions of low cytotoxicity. We employed a pseudotyped lentiviral vector (LVs) encoding the luciferase reporter gene and exhibiting the S protein of SARS-CoV-2 at its surface, to infect human ACE2-expressing HEK293T cells. Pre-treatment of LVs with MB-PDI prevented infection at low micromolar MB concentrations and 1 min of illumination. These results reveal the potential of MB-PDI to reduce viral loads in the nasal cavity and oropharynx in the early stages of COVID-19, which may be employed to curb the transmission and severity of the disease.

Photodynamic disinfection and its role in controlling infectious diseases.

Photodynamic therapy is witnessing a revival of its origins as a response to the rise of multi-drug resistant infections and the shortage of new classes of antibiotics. Photodynamic disinfection (PDDI) of microorganisms is making progresses in preclinical models and in clinical cases, and the perception of its role in the clinical armamentarium for the management of infectious diseases is changing. We review the positioning of PDDI from the perspective of its ability to respond to clinical needs. Emphasis is placed on the pipeline of photosensitizers that proved effective to inactivate biofilms, showed efficacy in animal models of infectious diseases or reached clinical trials. Novel opportunities resulting from the COVID-19 pandemic are briefly discussed. The molecular features of promising photosensitizers are emphasized and contrasted with those of photosensitizers used in the treatment of solid tumors. The development of photosensitizers has been accompanied by the fabrication of a variety of affordable and customizable light sources. We critically discuss the combination between photosensitizer and light source properties that may leverage PDDI and expand its applications to wider markets. The success of PDDI in the management of infectious diseases will ultimately depend on the efficacy of photosensitizers, affordability of the light sources, simplicity of the procedures, and availability of fast and efficient treatments.

Photodynamic Inactivation of Foodborne Bacteria: Screening of 32 Potential Photosensitizers.

The development of novel antimicrobial technologies for the food industry represents an important strategy to improve food safety. Antimicrobial photodynamic disinfection (aPDD) is a method that can inactivate microbes without the use of harsh chemicals. aPDD involves the administration of a non-toxic, light-sensitive substance, known as a photosensitizer, followed by exposure to visible light at a specific wavelength. The objective of this study was to screen the antimicrobial photodynamic efficacy of 32 food-safe pigments tested as candidate photosensitizers (PSs) against pathogenic and food-spoilage bacterial suspensions as well as biofilms grown on relevant food contact surfaces. This screening evaluated the minimum bactericidal concentration (MBC), minimum biofilm eradication concentration (MBEC), and colony forming unit (CFU) reduction against Salmonella enterica, methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas fragi, and Brochothrix thermosphacta. Based on multiple characteristics, including solubility and the ability to reduce the biofilms by at least 3 log10 CFU/sample, 4 out of the 32 PSs were selected for further optimization against S. enterica and MRSA, including sunset yellow, curcumin, riboflavin-5'-phosphate (R-5-P), and erythrosin B. Optimized factors included the PS concentration, irradiance, and time of light exposure. Finally, 0.1% w/v R-5-P, irradiated with a 445 nm LED at 55.5 J/cm2, yielded a "max kill" (upwards of 3 to 7 log10 CFU/sample) against S. enterica and MRSA biofilms grown on metallic food contact surfaces, proving its potential for industrial applications. Overall, the aPDD method shows substantial promise as an alternative to existing disinfection technologies used in the food processing industry.

The Effectiveness of Laser Applications and Photodynamic Therapy on Relevant Periodontal Pathogens (Aggregatibacter actinomycetemcomitans) Associated with Immunomodulating Anti-rheumatic Drugs.

Considering the current context of the increasing resistance of bacterial species to antibiotics and other antimicrobial agents, a major objective is to develop other antimicrobial approaches, which would be able to inactivate pathogens with considerable effectiveness. Two such methods are photodynamic disinfection therapy and laser irradiation. In view of the immunocompromised status of some patients under immunosuppressive therapy and potential drug interactions that can be established between systemic antimicrobial agents, the research of local, minimally invasive methods of inactivating periodontal pathogens in the context of these systemic therapies with modifying drugs of the immune response is justified. This in vitro study evaluated the antimicrobial action of a diode laser, wavelength 940 nm, and photodisinfection therapy at 670 nm (photosensitizer, 3,7 dimethyl phenothiazine chloride) on a type strain of Aggregatibacter actinomycetemcomitans, a known periodontal pathogen, in the presence and absence of active substances used in autoimmune disease therapy (Etanercept, Infliximab, Metothrexate). The association of a conventional antirheumatic drug with anti-TNF-α therapy determined a significantly greater inhibition of the strain of A. actinomycetemcomitans compared to monotherapy, in vitro. Photodisinfection caused a significant reduction in bacterial burden after a 30 s exposure in vitro, regardless of the pharmaceutical associations of biological and conventional disease-modifying antirheumatic drugs (DMARDs). Irradiation with a diode laser for 30 s at a power of 5 W caused a greater reduction compared to irradiation with 1 W. The application of laser and photodisinfection induced a significant reduction in Aggregatibacter actinomycetemcomitans in vitro and could be considered important adjunctive measures for the eradication of this oral pathogen in the context of immunomodulating therapy.

Green phytoextracts as natural photosensitizers in LED-based photodynamic disinfection of multidrug-resistant bacteria in wastewater effluent.

The photodynamic treatment (PDT) process is a promising technology to control emerging pollutants and antimicrobial resistance problems in the water environment. The reactive oxygen species (ROS) produced when natural and nontoxic photosensitizers (PS) are exposed to light are the key functional components of the PDT process that can effectively achieve microbial inactivation with minimal negative impact. This study examined the application of green phytoextracts from two plants, Chamaecyparis obtusa and Moringa oleifera, as natural photosensitizers for the white light-emitting diode (LED) based photodynamic disinfection of multidrug-resistant (MDR) and total coliforms (TC) from secondary effluent in full-scale municipal wastewater treatment plants. Gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy showed that the phytoextracts contained 57 compounds, particularly aromatic and phenolic hydroxyl compounds. The phytoextracts showed an excellent activity as a PS compared to the intrinsic antibacterial effect. Under a light intensity of 17 mW/cm2, the complete inactivation (6.55 Log CFU/mL) was observed at an irradiation time of 100 min for Escherichia coli ART-2 and 80 min for Staphylococcus aureus, meaning that E. coli was resistant. The light intensity was an important factor influencing photodynamic disinfection. For the complete disinfection of TC satisfying the water reclamation regulation, the irradiation time requirement was 20 min under a light intensity of 80 mW/cm2. During the photodynamic reaction, a significant amount of ROS was generated from the phytoextracts as the light irradiation time was increased. The major ROS was singlet oxygen (1O2, Type II) during the initial 40 min of reaction time and hydroxyl radical (•OH, Type I) after 40 min until complete inactivation.

Photodynamic inactivation of multidrug-resistant bacteria in wastewater effluent using green phytochemicals as a natural photosensitizer.

The control of multidrug-resistant bacteria (MDRB) is a great challenge in the 21st century. Photodynamic treatment (PDT) is one of the promising approaches to control MDRB. In the process, powerful oxidants such as reactive oxygen species (ROS) are produced, which cause cytotoxic damage and cell death of bacteria. This study examined a new and environment-friendly strategy for the photodynamic inactivation of two MDRB (Escherichia coli and Staphylococcus aureus) and total coliform (TC) in wastewater effluent using two phytochemicals, pyrogallol (PGL) and terpinolene (TPN), along with white and blue light-emitting diode (LED) light. Fourier-transform infrared spectroscopy (FTIR) of the phytochemicals confirmed the presence of different phenolic and aromatic compounds, which can enhance the generation of ROS alongside inactivating the bacterial cells. In the PDT process, white LED light was more active in controlling MDRB than blue LED light. After 80 min irradiation with white LED light (17 mW/cm2), the MDRB bacteria were eradicated completely at a minimum inhibitory concentration (MIC) dose (0.156 mg/mL for E. coli and 0.078 mg/mL for S. aureus) of PGL. In addition, light intensity was an important parameter in photodynamic disinfection. The TC in the secondary effluent was inactivated completely by both phytochemicals after 60 min of exposure to white LED light with an intensity of 80 mW/cm2. The photosensitizing activity of phytochemicals was analyzed by a bactericidal and imidazole-RNO assay. These assays showed that PGL contributed to the generation of •OH radicals, whereas TPN produced 1O2 in the PDT process. Transmission electron microscopy (TEM) confirmed bacterial cell disruption after treatment. Overall, PDT using the phytochemicals as PS is a sustainable approach to control the MDRB and TC in wastewater successfully.

Evaluation of effect of two different functionalized nanoparticle photodynamic therapy on nanohardness of root dentin-An in vitro study.

INTRODUCTION: The aim of this study was to evaluate the effect of functionalized nanoparticle photodynamic therapy on Nano hardness of root dentin METHODOLOGY: Fifty single rooted lower premolars were decoronated and sectioned into two halves. Then the samples were embedded horizontally in to the acrylic resin to expose the dentin surface. Baseline nanohardness was done at midroot level using a Nanohardness tester. Exposed dentin surfaces were immersed in the following irrigating solutions Post treatment nanohardness testing was done and results were analyzed statistically RESULTS: In general, all the samples in their respective groups had significant change in nanohardness following immersion in irrigant solutions except in NaOCl + EDTA and saline group. CSRB-np and PLGA-MBnp showed increased nanohardness (P = 0.005 and P = 0.007 respectively). Whereas NaOCl + EDTA + CHX showed decrease in nanohardness (P = 0.04). With regards to Modulus of elasticity (MOE), CSRB-np showed significant difference (P = 0.002) compared to the other groups. MOE increased in CSRB-np and PLGA-MBnp while it decreased in all the other groups. CONCLUSION: In this study, the improvement of nanohardness and modulus of elasticity following the immersion of root dentin in CSRB-np solution was demonstrated.