Potentiation of photoinactivation of Gram-positive and Gram-negative bacteria mediated by six phenothiazinium dyes by addition of azide ion

Highly Efficient Quenching of Singlet Oxygen by DNA Origami Nanostructures

DNA origami nanostructures (DONs) are able to scavenge reactive oxygen species (ROS) and their scavenging efficiency toward ROS radicals was shown to be comparable to that of genomic DNA. Herein, we demonstrate that DONs are highly efficient singlet oxygen quenchers outperforming double-stranded (ds) DNA by several orders of magnitude. To this end, a ROS mixture rich in singlet oxygen is generated by light irradiation of the photosensitizer methylene blue and its cytotoxic effect on Escherichia coli cells is quantified in the presence and absence of DONs. DONs are found to be vastly superior to dsDNA in protecting the bacteria from ROS-induced damage and even surpass established ROS scavengers. At a concentration of 15 nM, DONs are about 50 000 times more efficient ROS scavengers than dsDNA at an equivalent concentration. This is attributed to the dominant role of singlet oxygen, which has a long diffusion length and reacts specifically with guanine. The dense packing of the available guanines into the small volume of the DON increases the overall quenching probability compared to a linear dsDNA with the same number of base pairs. DONs thus have great potential to alleviate oxidative stress caused by singlet oxygen in diverse therapeutic settings.

Kinetics of dye decolorization using heterogeneous catalytic system with immobilized Achromobacter xylosoxidans DDB6

Textile effluents containing toxic dyes must be treated effectively before discharge to prevent adverse environmental impacts. Traditional physical and chemical treatment methods are costly and generate secondary pollutants. In contrast, biological treatment is a more suitable, clean, versatile, eco-friendly, and cost-effective technique for treating textile effluent. It is well established that indigenous microbial populations present in effluents can effectively degrade toxic dyes. In this regard, Achromobacter xylosoxidans DDB6 was isolated from the effluent sample to decolorize crystal violet (CV), Coomassie brilliant blue (CBB), and alizarin red (AR) by 67.20%, 28.58%, and 20.41%, respectively. The growth parameters of A. xylosoxidans DDB6 in media supplemented with 100 ppm of various dyes were determined using the modified Gompertz growth model. The immobilized cells in calcium alginate beads showed apparent decolorization rate constant of 0.27, 0.18, and 0.13 h-1 for CV, CBB, and AR, respectively. The immobilized cells in a packed bed reactor with an optimum flow rate of 0.5 mL/min were used to treat 100 ppm of CV with a percentage decolorization of 79.47% after three cycles. Based on the findings, A. xylosoxidans DDB6 could be effectively used for decolorization of various dyes.

Antimicrobial photodynamic therapy against oral biofilm: influencing factors, mechanisms, and combined actions with other strategies

Oral biofilms are a prominent cause of a wide variety of oral infectious diseases which are still considered as growing public health problems worldwide. Oral biofilms harbor specific virulence factors that would aggravate the infectious process and present resistance to some traditional therapies. Antimicrobial photodynamic therapy (aPDT) has been proposed as a potential approach to eliminate oral biofilms via in situ-generated reactive oxygen species. Although numerous types of research have investigated the effectiveness of aPDT, few review articles have listed the antimicrobial mechanisms of aPDT on oral biofilms and new methods to improve the efficiency of aPDT. The review aims to summarize the virulence factors of oral biofilms, the progress of aPDT in various oral biofilm elimination, the mechanism mediated by aPDT, and combinatorial approaches of aPDT with other traditional agents.

Photodynamic therapy: Innovative approaches for antibacterial and anticancer treatments

Photodynamic therapy is an alternative treatment mainly for cancer but also for bacterial infections. This treatment dates back to 1900 when a German medical school graduate Oscar Raab found a photodynamic effect while doing research for his doctoral dissertation with Professor Hermann von Tappeiner. Unexpectedly, Raab revealed that the toxicity of acridine on paramecium depends on the intensity of light in his laboratory. Photodynamic therapy is therefore based on the administration of a photosensitizer with subsequent light irradiation within the absorption maxima of this substance followed by reactive oxygen species formation and finally cell death. Although this treatment is not a novelty, there is an endeavor for various modifications to the therapy. For example, selectivity and efficiency of the photosensitizer, as well as irradiation with various types of light sources are still being modified to improve final results of the photodynamic therapy. The main aim of this review is to summarize anticancer and antibacterial modifications, namely various compounds, approaches, and techniques, to enhance the effectiveness of photodynamic therapy.

Antimicrobial Photodynamic Effect of Cross-Kingdom Microorganisms with Toluidine Blue O and Potassium Iodide

Streptococcus mutans (S. mutans) and Candida albicans (C. albicans) are prominent microbes associated with rapid and aggressive caries. In the present study, we investigated the antimicrobial efficacy, cytotoxicity, and mechanism of toluidine blue O (TBO)-mediated antimicrobial photodynamic therapy (aPDT) and potassium iodide (KI). The dependence of KI concentration, TBO concentration and light dose on the antimicrobial effect of aPDT plus KI was determined. The cytotoxicity of TBO-mediated aPDT plus KI was analyzed by cell counting kit-8 (CCK-8) assay. A singlet oxygen (1O2) probe test, time-resolved 1O2 detection, and a 1O2 quencher experiment were performed to evaluate the role of 1O2 during aPDT plus KI. The generation of iodine and hydrogen peroxide (H2O2) were analyzed by an iodine starch test and Amplex red assay. The anti-biofilm effect of TBO-mediated aPDT plus KI was also evaluated by counting forming unit (CFU) assay. KI could potentiate TBO-mediated aPDT against S. mutans and C. albicans in planktonic and biofilm states, which was safe for human dental pulp cells. 1O2 measurement showed that KI could quench 1O2 signals, implicating that 1O2 may act as a principal mediator to oxidize excess iodide ions to form iodine and H2O2. KI could highly potentiate TBO-mediated aPDT in eradicating S. mutans and C. albicans due to the synergistic effect of molecular iodine and H2O2.

The evolution of clinical guidelines for antimicrobial photodynamic therapy of skin

Antimicrobial photodynamic therapy has become an important component in the treatment of human infection. This review considers historical guidelines, and the scientific literature to envisage what future clinical guidelines for treating skin infection might include. Antibiotic resistance, vertical and horizontal infection control strategies and a range of technologies effective in eradicating microbes without building up new resistance are described. The mechanism of action of these treatments and examples of their clinical use are also included. The research recommendations of NICE Guidelines on the dermatological manifestations of microbial infection were also reviewed to identify potential applications for PDT. The resistance of some microbes to antibiotics can be halted, or even reversed through the use of supplementary drugs, and so they are likely to persist as a treatment of infection. Conventional PDT will undoubtedly continue to be used for a range of skin conditions given existing healthcare infrastructure and a large evidence base. Daylight PDT may find broader antimicrobial applications than just Acne and Cutaneous Leishmaniasis, and Ambulatory PDT devices could become popular in regions where resources are limited or daylight exposure is not possible or inappropriate. Nanotheranostics were found to be highly relevant, and often include PDT, however, new treatments and novel applications and combinations of existing treatments will be subject to Clinical Trials.

In Vivo Potentiation of Antimicrobial Photodynamic Therapy in a Mouse Model of Fungal Infection by Addition of Potassium Iodide

Antimicrobial photodynamic inactivation (aPDI) involves the use of a nontoxic dye or photosensitizer excited with visible light to produce reactive oxygen species that can kill all classes of microorganisms. Antimicrobial photodynamic therapy (aPDT) can be used in vivo as an alternative therapeutic strategy to treat localized infections due to its ability to selectively kill microbes while preserving host mammalian cells. aPDI can be potentiated by the addition of the nontoxic inorganic salt potassium iodide (KI). KI is an approved drug for antifungal therapy. The mechanism of potentiation with iodide is likely to be singlet oxygen addition to iodide to form iodine radicals, hydrogen peroxide, and molecular iodine. A previous chapter in this volume described potentiation of aPDI in vitro by addition of KI, while in this chapter we address the ability of KI to potentiate aPDT in vivo using an animal model of localized fungal infection. We employed oral candidiasis in immunosuppressed mice caused by a bioluminescent strain of Candida albicans and monitored by bioluminescence imaging.

Contributions of photochemistry to bio-based antibacterial polymer materials

Surgical site infections constitute a major health concern that may be addressed by conferring antibacterial properties to surgical tools and medical devices via functional coatings. Bio-sourced polymers are particularly well-suited to prepare such coatings as they are usually safe and can exhibit intrinsic antibacterial properties or serve as hosts for bactericidal agents. The goal of this Review is to highlight the unique contribution of photochemistry as a green and mild methodology for the development of such bio-based antibacterial materials. Photo-generation and photo-activation of bactericidal materials are illustrated. Recent efforts and current challenges to optimize the sustainability of the process, improve the safety of the materials and extend these strategies to 3D biomaterials are also emphasized.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

A rapid antimicrobial photodynamic water treatment strategy utilizing a xanthene dye with subsequent removal by Goethite Nanoparticles

Although widely accepted as a water sterilisation technique, chlorination results in the production of potentially harmful by-products, mainly Trihalomethanes. Furthermore, the chlorination process requires specialised infrastructure, management and high costs. In this research paper a potential alternative sterilisation technique was investigated. This rapid three-step process utilized Goethite Nanoparticles and the photosensitising capabilities of a xanthene dye. Rose Bengal (RB) a compound primarily used as a stain to diagnose damaged tissue in the eye was utilized under visible light excitation to sterilise water containing gram-positive Staphylococcus aureus and Bacillus cereus. Bacterial reductions (cfu/ml) of up to 6log10 are reported at RB concentrations of 0.5 mg/L and 10 mg/L for S. aureus and B. cereus, respectively. Goethite Nanoparticles (GNP's), an iron oxyhydroxide, were synthesised by co-precipitation of iron salts and used to adsorb RB post-sterilisation. Poly-vinyl Alcohol (PVA) functionalised GNP's were synthesised to highlight the adsorbent capabilities of the GNP surface. The adsorption capacity for uncoated GNPs was 476.19 mg/g, this reduced to 170.4 mg/g for PVA-GNP's, highlighting the highly porous nature of the synthesised GNP surface. Adsorption was optimal in slightly acidic conditions (pH5-6). The adsorption parameters best followed Lagergens Pseudo-second order kinetics with correlation coefficients close to unity. At the highest envisaged RB concentration (10 mg/L) approximately 20 mg/L GNP's was required to remove the dye from solution post-treatment. Flame Atomic Absorption analysis of the water post-removal revealed Iron concentrations of 0.058 mg/L. This correlates to removal efficacy of 99.71% with residual iron levels below the EU recommended limit of 0.2 mg/L.

Antimicrobial Photodynamic Approach in the Inactivation of Viruses in Wastewater: Influence of Alternative Adjuvants

Pathogenic viruses are frequently present in marine and estuarine waters, due to poor wastewater (WW) treatments, which consequently affect water quality and human health. Chlorination, one of the most common methods used to ensure microbiological safety in tertiarily treated effluents, may lead to the formation of toxic chemical disinfection by-products on reaction with organic matter present in the effluents. Antimicrobial photodynamic therapy (aPDT) can be a promising disinfecting approach for the inactivation of pathogens, without the formation of known toxic by-products. Additionally, some studies have reported the potentiator effect on aPDT of some compounds, such as potassium iodide (KI) and hydrogen peroxide (H2O2). In the present study, the aPDT efficiency of a PS formulation constituted of five cationic porphyrins (Form) in the inactivation of E. coli T4-like bacteriophage, a model of mammalian viruses, in different aqueous matrices with different organic matter content, was evaluated. Photoinactivation studies were performed at different concentrations of Form and in the presence of the adjuvants KI and H2O2. The results showed that the efficiency of bacteriophage photoinactivation is correlated with the Form concentration, the amount of the organic matter in WW, and the adjuvant type. Form can be an effective alternative to controlling viruses in WW, particularly if combined with H2O2, allowing to significantly reduce PS concentration and treatment time. When combined with KI, the Form is less effective in inactivating T4-like bacteriophage in WW.

The photosensitiser azure A disrupts mitochondrial bioenergetics through intrinsic and photodynamic effects

Azure A (AA) is a cationic molecule of the class of phenothiazines that has been applied in vitro as a photosensitising agent in photodynamic antimicrobial chemotherapy. It is a di-demethylated analogue of methylene blue (MB), which has been demonstrated to be intrinsically and photodynamically highly active on mitochondrial bioenergetics. However, as far as we know, there are no studies about the photodynamic effects of AA on mammalian mitochondria. Therefore, this investigation aimed to characterise the intrinsic and photodynamic acute effects of AA (0.540 μM) on isolated rat liver mitochondria, isolated hepatocytes, and isolated perfused rat liver. The effects of AA were assessed by evaluating several parameters of mitochondrial bioenergetics, oxidative stress, cell viability, and hepatic energy metabolism. The photodynamic effects of AA were assessed under simulated hypoxic conditions, a suitable way for mimicking the microenvironment of hypoxic solid tumour cells. AA interacted with the mitochondria and, upon photostimulation (10 min of light exposure), produced toxic amounts of reactive oxygen species (ROS), which damaged the organelle, as demonstrated by the high levels of lipid peroxidation and protein carbonylation. The photostimulated AA also depleted the GSH pool, which could compromise the mitochondrial antioxidant defence. Bioenergetically, AA photoinactivated the complexes I, II, and IV of the mitochondrial respiratory chain and the F1FO-ATP synthase complex, sharply inhibiting the oxidative phosphorylation. Upon photostimulation (10 min of light exposure), AA reduced the efficiency of mitochondrial energy transduction and oxidatively damaged lipids in isolated hepatocytes but did not decrease the viability of cells. Despite the useful photobiological properties, AA presented noticeable dark toxicity on mitochondrial bioenergetics, functioning predominantly as an uncoupler of oxidative phosphorylation. This harmful effect of AA was evidenced in isolated hepatocytes, in which AA diminished the cellular ATP content. In this case, the cells exhibited signs of cell viability reduction in the presence of high AA concentrations, but only after a long time of incubation (at least 90 min). The impairments on mitochondrial bioenergetics were also clearly manifested in intact perfused rat liver, in which AA diminished the cellular ATP content and stimulated the oxygen uptake. Consequently, gluconeogenesis and ureogenesis were strongly inhibited, whereas glycogenolysis and glycolysis were stimulated. AA also promoted the release of cytosolic and mitochondrial enzymes into the perfusate concomitantly with inhibition of oxygen consumption. In general, the intrinsic and photodynamic effects of AA were similar to those of MB, but AA caused some distinct effects such as the photoinactivation of the complex IV of the mitochondrial respiratory chain and a diminution of the ATP levels in the liver. It is evident that AA has the potential to be used in mitochondria-targeted photodynamic therapy, even under low oxygen concentrations. However, the fact that AA directly disrupts mitochondrial bioenergetics and affects several hepatic pathways that are linked to ATP metabolism, along with its ability to perturb cellular membranes and its little potential to reduce cell viability, could result in significant adverse effects especially in long-term treatments.

A novel tricationic fullerene C60 as broad-spectrum antimicrobial photosensitizer: mechanisms of action and potentiation with potassium iodide

A novel amphiphilic photosensitizing agent based on a tricationic fullerene C₆₀ (DMC₆₀³⁺) was efficiently synthesized from its non-charged analogue MMC₆₀. These fullerenes presented strong UV absorptions, with a broad range of less intense absorption up to 710 nm. Both compounds showed low fluorescence emission and were able to photosensitize the production of reactive oxygen species. Furthermore, photodecomposition of L-tryptophan sensitized by both fullerenes indicated an involvement of type II pathway. DMC₆₀³⁺ was an effective agent to produce the photodynamic inactivation (PDI) of Staphylococcus aureus, Escherichia coli and Candida albicans. Mechanistic insight indicated that the photodynamic action sensitized by DMC₆₀³⁺ was mainly mediated by both photoprocesses in bacteria, while a greater preponderance of the type II pathway was found in C. albicans. In presence of potassium iodide, a potentiation of PDI was observed due to the formation of reactive iodine species. Therefore, the amphiphilic DMC₆₀³⁺ can be used as an effective potential broad-spectrum antimicrobial photosensitizer.

Antimicrobial and antibiofilm photodynamic therapy against vancomycin resistant Staphylococcus aureus (VRSA) induced infection in vitro and in vivo

Biofilm mediated infection caused by multi-drug resistant bacteria are difficult to treat since it protects the microorganisms by host defense system, making them resistant to antibiotics and other antimicrobial agents. Combating such type of nosocomial infection, especially in immunocompromised patients, is an urgent need and foremost challenge faced by clinicians. Therefore, antimicrobial photodynamic therapy (aPDT) has been intensely pursued as an alternative therapy for bacterial infections. aPDT leads to the generation of reactive oxygen species (ROS) that destroy bacterial cells in the presence of a photosensitizer, visible light and oxygen. Here, we elucidated a possibility of its clinical application by reducing the treatment time and exposing curcumin to 20 J/cm² of blue laser light, which corresponds to only 52 s to counteract vancomycin resistant Staphylococcus aureus (VRSA) both in vitro and in vivo. To understand the mechanism of action, the generation of total reactive oxygen species (ROS) was quantified by 2'-7'-dichlorofluorescein diacetate (DCFH-DA) and the type of phototoxicity was confirmed by fluorescence spectroscopic analysis. The data showed more production of singlet oxygen, indicating type-II phototoxicity. Different anti-biofilm assays (crystal violet and congo red assays) and microscopic studies were performed at sub-MIC concentration of curcumin followed by treatment with laser light against preformed biofilm of VRSA. The result showed significant reduction in the preformed biofilm formation. Finally, its therapeutic potential was validated in skin abrasion wistar rat model. The result showed significant inhibition of bacterial growth. Furthermore, immunomodulatory analysis with rat serum was performed. A significant reduction in expression of proinflammatory cytokines TNF-α and IL-6 were observed. Hence, we conclude that curcumin mediated aPDT with 20 J/cm² of blue laser treatment (for 52 s) could be used against multi-drug resistant bacterial infections and preformed biofilm formation as a potential therapeutic approach.

Photodynamic therapy to control microbial biofilms

Microorganisms thrive in well-organized biofilm ecosystems. Biofilm-associated cells typically show increased resistance to antibiotics and contribute significantly to treatment failure. This has prompted investigations aimed at developing advanced and novel antimicrobial approaches that could effectively overcome the shortcomings associated with conventional antibiotic therapy. Studies are ongoing to develop effective curative strategies ranging from the use of peptides, small molecules, nanoparticles to bacteriophages, sonic waves, and light energy targeting various structural and physiological aspects of biofilms. In photodynamic therapy, a light source of a specific wavelength is used to irradiate non-toxic photosensitizers such as tetrapyrroles, synthetic dyes or, naturally occurring compounds to generate reactive oxygen species that can exert a lethal effect on the microbe especially by disrupting the biofilm. The photosensitizer preferentially binds to and accumulates in the microbial cells without causing any damage to the host tissue. Currently, photodynamic therapy is increasingly being used for the treatment of oral caries and dental plaque, chronic wound infections, infected diabetic foot ulcers, cystic fibrosis, chronic sinusitis, implant device-associated infections, etc. This approach is recognized as safe, as it is non-toxic and minimally invasive, making it a reliable, realistic, and promising therapeutic strategy for reducing the microbial burden and biofilm formation in chronic infections. In this review article, we discuss the current and future potential strategies of utilizing photodynamic therapy to extend our ability to impede and eliminate biofilms in various medical conditions.

Photochemistry of the Organoselenium Compound Ebselen: Direct Photolysis and Reaction with Active Intermediates of Conventional Reactive Species Sensitizers and Quenchers

Ebselen (EBS), 2-phenyl-1,2-benzisoselenazol-3(2H)-one, is an organoselenium pharmaceutical with antioxidant and anti-inflammatory properties. Furthermore, EBS is an excellent scavenger of reactive oxygen species. This property complicates conventional protocols for sensitizing and quenching reactive species because of potential generation of active intermediates that quickly react with EBS. In this study, the photochemical reactivity of EBS was investigated in the presence of (1) ¹O₂ and ^•OH sensitizers [rose Bengal (RB), perinaphthanone, and H₂O₂] and (2) reactive species scavenging and quenching agents (sorbic acid, isopropanol, sodium azide, and tert-butanol) that are commonly employed to study photodegradation mechanisms and kinetics. The carbon analogue of EBS, namely, 2-phenyl-3H-isoindol-1-one, was included as a reference compound to confirm the impact of the selenium atom on EBS photochemical reactivity. EBS does not undergo acid dissociation, but pH-dependent kinetics were observed in RB-sensitized solutions, suggesting EBS reaction with active intermediates (³RB^2-*, O₂^•-, and H₂O₂) that are not kinetically relevant for other compounds. In addition, the observed rate constant of EBS increased in the presence of sorbic acid, isopropanol, and sodium azide. These findings suggest that conventional reactive species sensitizers, scavengers, and quenchers need to be carefully applied to highly reactive organoselenium compounds to account for reactions that are typically slow for other organic contaminants.

Fatty Acid Conjugates of Toluidine Blue O as Amphiphilic Photosensitizers: Synthesis, Solubility, Photophysics and Photochemical Properties†

Toluidine blue O (TBO) is a water-soluble photosensitizer that has been used in photodynamic antimicrobial and anticancer treatments, but suffers from limited solubility in hydrophobic media. In an effort to incrementally increase TBO's hydrophobicity, we describe the synthesis of hexanoic (TBOC6) and myristic (TBOC14) fatty acid derivatives of TBO formed in low to moderate percent yields by condensation with the free amine site. Covalently linking 6 and 14 carbon chains led to modifications of not only TBO's solubility, but also its photophysical and photochemical properties. TBOC6 and TBOC14 derivatives were more soluble in organic solvents and showed hypsochromic shifts in their absorption and emission bands. The solubility in phosphate buffer solution was low for both TBOC6 and TBOC14, but unexpectedly slightly greater in the latter. Both TBOC6 and TBOC14 showed decreased triplet excited-state lifetimes and singlet oxygen quantum yields in acetonitrile, which was attributed to heightened aggregation of these conjugates particularly at high concentrations due to the hydrophobic "tails." While in diluted aqueous buffer solution, indirect measurements showed similar efficiency in singlet oxygen generation for TBOC14 compared to TBO. This work demonstrates a facile synthesis of fatty acid TBO derivatives leading to amphiphilic compounds with a delocalized cationic "head" group and hydrophobic "tails" for potential to accumulate into biological membranes or membrane/aqueous interfaces in PDT applications.

π-Extended Donor-Acceptor Porphyrins and Metalloporphyrins for Antimicrobial Photodynamic Inactivation

Free base, zinc and palladium π‐extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in antimicrobial photodynamic therapy (aPDT). Their efficacy, assessed by photophysical and in vitro photobiological studies on Gram‐positive bacteria, was found to depend on metal coordination, showing a dramatic enhancement of photosensitizing activity for the palladium complex.

Curcumin induced photodynamic therapy mediated suppression of quorum sensing pathway of Pseudomonas aeruginosa: An approach to inhibit biofilm in vitro

OBJECTIVE

The objective of this study was to inhibit the Pseudomonas aeruginosa biofilm through curcumin-mediated antimicrobial photodynamic therapy (A-PDT).

BACKGROUND

The mechanism behind A-PDT mediated photoinactivation depend upon reactive oxygen species (ROS) production, like singlet oxygen and free radicals.

METHODS

To evaluate the antibacterial efficacy of curcumin induced A-PDT on P. aeruginosa by colony forming unit (CFU) while antibiofilm action was determined by the use of crystal violet, XTT, congored binding assay and confocal laser scanning microscope (CLSM).

RESULTS

We found that curcumin with 10 J/cm² of light reduces P. aeruginosa biofilm more efficiently than without light. Extracellular polymeric substances (EPS) production was also reduced by approx 94 % with 10 J/cm² of light dose. CLSM images showed that the thickness of biofilms were reduced from >30 μm to <5 μm after treatment with curcumin followed by 10 J/cm² of light irradiation. Curcumin showed better bacteriostatic activity than bactericidal activity. Singlet oxygen is primarily responsible for photodamage and cytotoxic reactions caused by curcumin-mediated APDT. Genes involved in quorum sensing (QS) pathway was also found to be inhibited after APDT. Curcumin with 5 J/cm² light inhibits QS genes and on increasing light dose i.e10 J/cm², we found a drastic reduction in gene expression.

CONCLUSION

We conclude that the curcumin mediated A-PDT inhibits biofilm formation ofP. aeruginosa through QS pathway by the action of singlet oxygen generation which in turn reduced EPS of the biofilm.

Mechanistic Insight into the Photodynamic Effect Mediated by Neutral Red and a New Azine Compound in Staphylococcus aureus Cells

The photodynamic activity of Neutral Red and the new monobrominated Neutral Red was studied in suspensions of Staphylococcus aureus. The effect of mannitol and sodium azide in the presence of 25 μm photosensitizer on lethal photosensitization were investigated. The results of the mechanistic evaluation of Neutral Red showed that both mannitol and sodium azide produced a completed protective effect after irradiation without significant differences between them. The evaluation of monobrominated Neutral Red also showed a protective effect of microorganisms with the addition of mannitol. Although sodium azide produced a protective effect of the photoinactivation, it was incomplete and less than that exhibited by mannitol. The results indicate that the starting reagent, Neutral Red, is a producer of radical species, acting through a type I mechanism, whereas the halogenated derivative of Neutral Red produced reactive oxygen species and a contribution of singlet molecular oxygen cannot be discarded in the photoinactivation of Staphylococcus aureus cells. These results, analyzed together with the previously evaluated properties of the dyes, allow us to explain the differences observed in the photoinactivation of Staphylococcus aureus mediated by both azine photosensitizers.

Susceptibility of oral bacteria to antibacterial photodynamic therapy

Effective methods for managing the oral microbiome are necessary to ensure not only the oral but also the systemic health of a human body. The purpose of this study was to determine the sensitivity of four photosensitizers (PSs) to blue light in six representative oral bacterial species that cause intraoral diseases. The following six strains were investigated: Actinomyces israelii, Enterococcus faecium, Fusobacterium nucleatum, Lactobacillus gasseri, Streptococcus mutans, Veillonella parvula. PS stock solutions (1 mg/ml) were prepared by dissolving curcumin and protoporphyrin-IX in dimethyl sulfoxide, and resazurin and riboflavin in distilled water. The inoculation of 20 ml of a bacterial suspension cultured for 24 hours was mixed with 1,980 ml of each test solution, and then a light source was placed in front of the mixture. The irradiation wavelength was 405 nm and its applied energy was 25.3 J. The independent-samples t-test and one-way analysis of variance within groups were performed to compare the antibacterial effects in the four PSs. The antibacterial susceptibility when using different PSs and visible blue-light irradiation differed between the bacterial strains. Antibacterial photodynamic therapy that includes light exposure and PSs can be used to control the oral bacteria strains related to oral disease.

Advances in aPDT based on the combination of a porphyrinic formulation with potassium iodide: Effectiveness on bacteria and fungi planktonic/biofilm forms and viruses

The increasing world-wide rate of antibiotic resistance as well as the capacity of microorganisms to form biofilms, have led to a higher incidence of mortal infections that require alternative methods for their control. Antimicrobial photodynamic therapy (aPDT) emerged as an effective solution against resistant strains. The present work aims to evaluate the aPDT efficiency of a photosensitizer (PS) based on a low-cost formulation constituted by five cationic porphyrins (FORM) and its potentiation effect by KI on a broad spectrum of microorganisms under white light (380–700 nm, 25 W/m[Formula: see text]. The aPDT assays were performed with different concentrations of FORM (0.1 to 5.0 [Formula: see text]M) and 100 mM of KI on planktonic and biofilm forms of gram-positive (methicillin resistant Staphylococcus aureus–MRSA) and gram-negative (Escherichia coli resistant to chloramphenicol and ampicillin) bacteria, of the fungi Candida albicans and on a T4-like bacteriophage as a mammalian virus model. The results indicate that the FORM alone is an efficient PS to photoinactivate not only gram-negative and gram-positive bacteria, but also C. albicans, in planktonic and biofilm forms, and T4-like phage at low concentrations (<5.0 [Formula: see text]M). The presence of KI enhanced the photodynamic effect of this FORM for all microorganisms on the planktonic form, allowing the reduction of PS concentration and treatment time. The results also show that the combination FORM/KI is highly efficient in the elimination of already well-established biofilms of E. coli,S. aureus and C. albicans. This effect is probably associated with longer-lived iodine reactive species produced during the aPDT treatment.

Sodium nitrite potentiates antimicrobial photodynamic inactivation: possible involvement of peroxynitrate

We have recently shown that a wide range of different inorganic salts can potentiate antimicrobial photodynamic inactivation (aPDI) and TiO2-mediated antimicrobial photocatalysis. Potentiation has been shown with azide, bromide, thiocyanate, selenocyanate, and most strongly, with iodide. Here we show that sodium nitrite can also potentiate broad-spectrum aPDI killing of Gram-positive MRSA and Gram-negative Escherichia coli bacteria. Literature reports have previously shown that two photosensitizers (PS), methylene blue (MB) and riboflavin, when excited by broad-band light in the presence of nitrite could lead to tyrosine nitration. Addition of up to 100 mM nitrite gave 6 logs of extra killing in the case of Rose Bengal excited by green light against E. coli, and 2 logs of extra killing against MRSA (eradication in both cases). Comparable results were obtained for other PS (TPPS4 + blue light and MB + red light). Some bacterial killing was obtained when bacteria were added after light using a functionalized fullerene (LC15) + nitrite + blue light, and tyrosine ester amide was nitrated using both "in" and "after" modes with all four PS. The mechanism could involve formation of peroxynitrate by a reaction between superoxide radicals and nitrogen dioxide radicals; formation of the latter species was demonstrated by spin trapping with nitromethane.

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.

Comparison of thiocyanate and selenocyanate for potentiation of antimicrobial photodynamic therapy

We have previously shown that antimicrobial photodynamic therapy (aPDT) mediated by different photosensitizers (PS) can be potentiated by a variety of inorganic salts. Potassium thiocyanate (KSCN) potentiated aPDT mediated by methylene blue (MB), while potassium selenocyanate (KSeCN) potentiated aPDT mediated by MB, Rose Bengal and the anionic porphyrin 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin dihydrochloride. However, the mechanisms of action that were proposed were fundamentally different. In the present study, we compare these two salts (KSCN and KSeCN) with different light-activated PS and different oxidative reactions for killing gram-positive and gram-negative bacteria. Overall KSeCN was more powerful than KSCN, and worked with a wider range of PS, while KSCN only worked with phenothiazinium salts. KSeCN produced killing when cells were added after light suggesting production of a semistable species called selenocyanogen (SeCN)2 . We tested three different oxidative reactions that can all potentially kill bacteria: lead tetraacetate (Pb[OAc]4 ); Fenton reagent (hydrogen peroxide [H2 O2 ] and ferrous sulfate) H2 O2 and horseradish peroxidase (HRP). In every case, KSeCN was substantially more effective (several logs) than KSCN in potentiating the bacterial killing. We conclude that (SeCN)2 is the mediator for aPDT using KSeCN, while sulfur trioxide radical anion is the mediator for KSCN using phenothiaziums. For H2 O2 /HRP with KSCN, hypothiocyanite is proposed to be the antibacterial agent in the literature, while hyposelenocyanite is said not to exist. Pb[OAc]4 is known to produce (SeCN)2 from KSeCN as well as the analogous (SCN)2 from KSCN. The mediators from Fenton reaction are unclear (pseudohalogen radical ions?) Both KSCN (which occurs naturally in the human body) and KSeCN may be clinically applicable.

Water Disinfection by Immobilized Photosensitizers

Fresh water shortage has become a global problem. A partial solution for this problem is the use of treated and disinfected wastewater for irrigation. However, most existing wastewater disinfection methods are based on the use of aggressive chemicals or power-consuming physical processes. Photodynamic eradication of waterborne bacteria by immobilized photosensitizers may be a good alternative to conventional methods. In the present work, the photosensitizers Rose Bengal sodium salt, Rose Bengal lactone, methylene blue, and hematoporphyrin were immobilized in polyethylene or polypropylene using a “green” method of co-extrusion, without addition of any chemicals, yielding polymeric strips and beads containing the photosensitizers. The antibacterial efficiency of these immobilized photosensitizers was tested against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli in batch and continuous regimes upon illumination with a white luminescent lamp. All examined photosensitizers demonstrated a good ability to decrease the bacterial concentration, up to their total eradication. Immobilized photosensitizers are proposed for batch or continuous disinfection of wastewater after secondary treatment.

Inorganic Salts and Antimicrobial Photodynamic Therapy: Mechanistic Conundrums?

We have recently discovered that the photodynamic action of many different photosensitizers (PSs) can be dramatically potentiated by addition of a solution containing a range of different inorganic salts. Most of these studies have centered around antimicrobial photodynamic inactivation that kills Gram-negative and Gram-positive bacteria in suspension. Addition of non-toxic water-soluble salts during illumination can kill up to six additional logs of bacterial cells (one million-fold improvement). The PSs investigated range from those that undergo mainly Type I photochemical mechanisms (electron transfer to produce superoxide, hydrogen peroxide, and hydroxyl radicals), such as phenothiazinium dyes, fullerenes, and titanium dioxide, to those that are mainly Type II (energy transfer to produce singlet oxygen), such as porphyrins, and Rose Bengal. At one extreme of the salts is sodium azide, that quenches singlet oxygen but can produce azide radicals (presumed to be highly reactive) via electron transfer from photoexcited phenothiazinium dyes. Potassium iodide is oxidized to molecular iodine by both Type I and Type II PSs, but may also form reactive iodine species. Potassium bromide is oxidized to hypobromite, but only by titanium dioxide photocatalysis (Type I). Potassium thiocyanate appears to require a mixture of Type I and Type II photochemistry to first produce sulfite, that can then form the sulfur trioxide radical anion. Potassium selenocyanate can react with either Type I or Type II (or indeed with other oxidizing agents) to produce the semi-stable selenocyanogen (SCN)₂. Finally, sodium nitrite may react with either Type I or Type II PSs to produce peroxynitrate (again, semi-stable) that can kill bacteria and nitrate tyrosine. Many of these salts (except azide) are non-toxic, and may be clinically applicable.

An Insight Into the Potentiation Effect of Potassium Iodide on aPDT Efficacy

Antimicrobial photodynamic therapy (aPDT) is gaining a special importance as an effective approach against multidrug-resistant strains responsible of fatal infections. The addition of potassium iodide (KI), a non-toxic salt, is recognized to increase the aPDT efficiency of some photosensitizers (PSs) on a broad-spectrum of microorganisms. As the reported cases only refer positive aPDT potentiation results, in this work we selected a broad range of porphyrinic and non-porphyrinic PSs in order to gain a more comprehensive knowledge about this aPDT potentiation by KI. For this evaluation were selected a series of meso-tetraarylporphyrins positively charged at meso positions or at β-pyrrolic positions and the non-porphyrinic dyes Methylene blue, Rose Bengal, Toluidine Blue O, Malachite Green and Crystal Violet; the assays were performed using a bioluminescent E. coli strain as a model. The results indicate that KI has also the ability to potentiate the aPDT process mediated by some of the cationic PSs [Tri-Py(+)-Me, Tetra-Py(+)-Me, Form, RB, MB, Mono-Py(+)-Me, β-ImiPhTPP, β-ImiPyTPP, and β-BrImiPyTPP] allowing a drastic reduction of the treatment time as well as of the PS concentration. However, the efficacy of some porphyrinic and non-porphyrinic PSs [Di-Py(+)-Me opp , Di-Py(+)-Me adj , Tetra-Py, TBO, CV, and MG] was not improved by the presence of the coadjuvant. For the PSs tested in this study, the ones capable to decompose the peroxyiodide into iodine (easily detectable by spectroscopy or by the visual appearance of a blue color in the presence of amylose) were the most promising ones to be used in combination with KI. Although these studies confirmed that the generation of 1O2 is an important fact in this process, the PS structure (charge number and charge position), aggregation behavior and affinity for the cell membrane are also important features to be taken in account.

Fullerenes as photosensitizers in photodynamic therapy: pros and cons

One class of carbon nanomaterials is the closed cages known as fullerenes. The first member to be discovered in 1985 was C60, called "buckminsterfullerene" as its cage structure resembled a geodesic dome. Due to their extended π-conjugation they absorb visible light, possess a high triplet yield and can generate reactive oxygen species upon illumination, suggesting a possible role of fullerenes in photodynamic therapy (PDT). Pristine C60 is highly hydrophobic and prone to aggregation, necessitating functionalization to provide aqueous solubility and biocompatibility. The most common functional groups attached are anionic (carboxylic or sulfonic acids) or cationic (various quaternary ammonium groups). Depending on the functionalization, these fullerenes can be designed to be taken up into cancer cells, or to bind to microbial cells (Gram-positive, Gram-negative bacteria, fungi). Fullerenes can be excited with a wide range of wavelengths, UVA, blue, green or white light. We have reported a series of functionalized fullerenes (C60, C70, C82) with attached polycationic chains and additional light-harvesting antennae that can be used in vitro and in animal models of localized infections. Advantages of fullerenes as photosensitizers are: (a) versatile functionalization; (b) light-harvesting antennae; (c) ability to undergo Type 1, 2, and 3 photochemistry; (d) electron transfer can lead to oxygen-independent photokilling; (e) antimicrobial activity can be potentiated by inorganic salts; (f) can self-assemble into supramolecular fullerosomes; (g) components of theranostic nanoparticles; (h) high resistance to photobleaching. Disadvantages include: (a) highly hydrophobic and prone to aggregation; (b) overall short wavelength absorption; (c) relatively high molecular weight; (d) paradoxically can be anti-oxidants; (e) lack of fluorescence emission for imaging.

Comparison of two functionalized fullerenes for antimicrobial photodynamic inactivation: Potentiation by potassium iodide and photochemical mechanisms

A new fullerene (BB4-PPBA) functionalized with a tertiary amine and carboxylic acid was prepared and compared with BB4 (cationic quaternary group) for antimicrobial photodynamic inactivation (aPDI). BB4 was highly active against Gram-positive methicillin resistant Staphylococcus aureus (MRSA) and BB4-PPBA was moderately active when activated by blue light. Neither compound showed much activity against Gram-negative Escherichia coli or fungus Candida albicans. Therefore, we examined potentiation by addition of potassium iodide. Both compounds were highly potentiated by KI (1-6 extra logs of killing). BB4-PPBA was potentiated more than BB4 against MRSA and E. coli, while for C. albicans the reverse was the case. Addition of azide potentiated aPDI mediated by BB4 against MRSA, but abolished the potentiation caused by KI with both compounds. The killing ability after light decayed after 24 h in the case of BB4, implying a contribution from hypoiodite as well as free iodine. Tyrosine was readily iodinated with BB4-PPBA plus KI, but less so with BB4. We conclude that the photochemical mechanisms of these two fullerenes are different. BB4-PPBA is more Type 2 (singlet oxygen) while BB4 is more Type 1 (electron transfer). There is also a possibility of direct bacterial killing by electron transfer, but this will require more study to prove.

Antimicrobial photodynamic inactivation is potentiated by the addition of selenocyanate: Possible involvement of selenocyanogen?

We previously showed that antimicrobial photodynamic inactivation (aPDI) of Gram-positive and Gram-negative bacteria mediated by the phenothiazinium dye, methylene blue (MB), was potentiated by the addition of potassium thiocyanate (10 mM). The mechanism was suggested to involve a singlet oxygen-mediated reaction with SCN to form sulfite and cyanide and then to produce sulfur trioxide radical anion. We now report that potassium selenocyanate (concentrations up to 100 mM) can also potentiate (up to 6 logs of killing) aPDI mediated by a number of different photosensitizers (PS): MB, rose bengal and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin dihydrochloride (as low as 200 nM). When a mixture of selenocyanate with these PS in solution was illuminated and then bacteria were added after the light, there was up to 6 logs of killing (Gram-negative > Gram-positive) but the antibacterial species decayed rapidly (by 20 minutes). Our hypothesis to explain this antibacterial activity is the formation of selenocyanogen (SeCN)2 by reaction with singlet oxygen (1 O2 ) as shown by quenching of 1 O2 by SeCN and increased photoconsumption of oxygen. The fact that lead tetraacetate reacted with SeCN (literature preparation of (SeCN)2 ) also produced a short-lived antibacterial species supports this hypothesis.

Susceptibility of sodA- and sodB-deficient Escherichia coli mutant towards antimicrobial photodynamic inactivation via the type I-mechanism of action

Photodynamic antimicrobial chemotherapy (PACT) is a multi-target method to inactivate pathogenic microorganisms by exciting a photosensitizer (PS) with visible light of appropriate wavelength in the presence of molecular oxygen (³O₂). There are two major pathways by which reactive oxygen species (ROS) are produced. In type I (T_I)-reactions, radicals such as superoxide (O₂˙^-) and hydroxyl radicals (˙OH) are generated by electron transfer. In type II (T_II)-reactions, highly reactive singlet oxygen (¹O₂) is produced by direct energy transfer. This study investigated the efficiency of PACT in Gram-negative Escherichia coli wild type (EC WT) and the mutant Escherichia coli PN134 (EC PN134) which is not able to produce SOD A and SOD B, by means of two different photosensitizers (PS) from different chemical classes with different ¹O₂ quantum yields: methylene blue (MB) and 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP). Mutants, which lack antioxidant enzymes, were particularly susceptible towards T_I-PACT. In the case of PACT with MB, quenching agents such as superoxide dismutase (SOD) and catalase (CAT) were sufficient for protecting both the wild type and the mutant, whereas they were not in PACT with TMPyP. The genetic levels of sodA and sodB were examined after photodynamic treatment regarding their potential resistance. This study showed that - under the photodynamic conditions presented in this study - expression of sodA and sodB was not directly influenced by PACT-generated oxidative stress, although SOD enzymes are part of the major defense machinery against oxidative stress and were thus expected to be upregulated. Overall the susceptibility of EC PN134 and EC WT differed towards photodynamic inactivation via T_I-mechanism of action. Thus, already existing defense mechanisms against ROS in bacteria might influence the susceptibility against T_I-PACT, while this was not the case using T_II-photosensitizers.

Phage Display of Dynamic Covalent Binding Motifs Enables Facile Development of Targeted Antibiotics

Antibiotic resistance of bacterial pathogens poses an increasing threat to the wellbeing of our society and urgently calls for new strategies for infection diagnosis and antibiotic discovery. The antibiotic resistance problem at least partially arises from extensive use of broad-spectrum antibiotics. Ideally, for the treatment of infection, one would like to use a narrow-spectrum antibiotic that specifically targets and kills the disease-causing strain. This is particularly important considering the commensal bacterial species that are beneficial and sometimes even critical to the health of a human being. In this contribution, we describe a phage display platform that enables rapid identification of peptide probes for specific bacterial strains. The phage library described herein incorporates 2-acetylphenylboronic acid moieties to elicit dynamic covalent binding to the bacterial cell surface. Screening of the library against live bacterial cells yields submicromolar and highly specific binders for clinical strains of Staphylococcus aureus and Acinetobacter baumannii that display antibiotic resistance. We further show that the identified peptide probes can be readily converted to bactericidal agents that deliver generic toxins to kill the targeted bacterial strain with high specificity. The phage display platform described here is applicable to a wide array of bacterial strains, paving the way to facile diagnosis and development of strain-specific antibiotics.

Catalase A is involved in the response to photooxidative stress in Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is the etiological agent of systemic and skin infections that are often difficult to treat. Photodynamic therapy (PDT) and, more recently, phototherapy (PT), are emerging among antimicrobial treatments to be combined with antibiotics. Visible light, either alone or combined with a photosensitizer (PS), elicits photooxidative stress that induces microbial death. The response of bacteria to phototherapy seems to involve the antioxidant machinery. This study relies on the effects of detoxifying catalase A (KatA) in response to PDT and PT-induced photooxidative stress.

METHODS

The photo- and photodynamic inactivation experiments have been targeted at P. aeruginosa PAO1 and its isogenic derivative katA^- mutant. The microorganisms were irradiated by a wide-spectrum halogen-tungsten lamp or light-emitting diodes (LEDs). Two photosensitizers, Tetrakis-(1-methyl-4-pyridyl)-21H, 23porphine, tetra-p-tosylate (TMPyP) porphyrin and Toluidine Blue O (TBO), were applied as part of the photodynamic approach.

RESULTS

P. aeruginosa katA^- mutant was more sensitive than wild-type strain PAO1 to wide-spectrum light and blue LED (464 nm) treatments. The complementation of KatA, in katA^- mutant, restored the light response of wild-type PAO1. Upon TBO treatment and irradiation by visible light (halogen lamp or LED), the sensitivity of katA^- mutant was significant higher (p = 0.028 and p = 0.045, respectively) than that of the PAO1 strain.

CONCLUSIONS

This study provides the first description of KatA in the response to photooxidative stress induced by photo- and photodynamic therapy.

Photodynamic inactivation assisted by localized surface plasmon resonance of silver nanoparticles: In vitro evaluation on Escherichia coli and Streptococcus mutans

Localized surface plasmon resonance (LSPR) of gold nanoparticles has been reported to increase the antimicrobial effect of the photodynamic therapy. Although silver nanoparticles (AgNPs) are an efficient growth inhibitor of microorganisms, no studies exploring LSPR of AgNPs to enhance the photodynamic inactivation (PDI) have been related. In this work, we described the LSPR phenomenon of AgNP sand investigated its interaction with riboflavin, a natural photosensitizer. We evaluated the use of AgNPs coated with pectin (p-AgNP) in riboflavin (Rb)-mediated PDI of Escherichia coli (Gram- bacteria) and Streptococcus mutans (Gram + bacteria) using a blue light-emitting diode (λ = 455 ± 20 nm) of optical power 200 mW. Irradiance was 90 mW/cm² and radiant exposure varied according to the time exposure. Uptake of Rb and p-AgNP by the cells was evaluated by measuring the supernatant absorption spectra of the samples. We observed that LSPR of p-AgNPs was able to enhance the riboflavin photodynamic action on S. mutans but not on E. coli, probably due to the lower uptake of Rb by E. coli. Taken together, our results provide insights to explore the use of the LPRS promoted by silver nanostructures to optimize antimicrobial PDI protocols.

Efficacy of photodynamic therapy against Streptococcus mutans biofilm: Role of singlet oxygen

In photodynamic therapy (PDT), killing is entirely based on the ROS generation and among different types of ROS generated during PDT, singlet oxygen is considered as the most potential as illustrated in many studies and therefore it is predominantly responsible for photodamage and cytotoxic reactions. The aim of this study was to check whether singlet oxygen (Type II photochemistry) is more potential than free radicals (Type I photochemistry) against Streptococcus mutans biofilm. We have taken two phenothiazinium dyes i.e. toluidine blue O (TBO) and new methylene blue (NMB). TBO was found to have better antibacterial as well as antibiofilm effect than NMB. Antibacterial effect was evaluated by colony forming unit while antibiofilm action by crystal violet and congo red binding assays. We have also evaluated the disruption of preformed biofilm by biofilm reduction assay, confocal laser electron and scanning electron microscopy. More singlet oxygen production was detected in case of TBO than NMB while more Free radical (HO) was produced by NMB than TBO. TBO showed better antibacterial as well as antibiofilm effect than NMB so; we conclude that potency of a photosensitizer is correlated with the capability to produce singlet oxygen.

Titania and silica nanoparticles coupled to Chlorin e6 for anti-cancer photodynamic therapy

In this study, light-sensitive photosensitizers (Chlorin e6, Ce6) were linked to TiO₂ and SiO₂ nanoparticles (NPs) in order to develop new kinds of NP-based drug delivery systems for cancer treatment by PDT. TiO₂ or SiO₂ NPs were modified either by the growth of a polysiloxane layer constituted of two silane reagents ((3-aminopropyl)triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS)) around the core (PEGylated NPs: TiO₂@4Si-Ce6-PEG, SiO₂@4Si-Ce6-PEG) or simply modified by APTES alone (APTES-modified NPs: TiO₂-APTES-Ce6, SiO₂-APTES-Ce6). Ce6 was covalently attached onto the modified TiO₂ and SiO₂ NPs via an amide bond. The absorption profile of the hybridized NPs was extended to the visible region of the light. The physicochemical properties of these NPs were explored by TEM, HR-TEM, XRD, FTIR and zeta potential. The photophysical characteristics including the light absorption, the fluorescence properties and the production reactive oxygen species (¹O₂ and HO) were also addressed. In vitro experiments on glioblastoma U87 cells were performed to evaluate the photodynamic efficiency of the new hybridized NPs. The cells were exposed to different concentrations of NPs and illuminated (λ_exc = 652 nm, fluence rate 10 J/cm²). In contrast to the PEGylated NPs, the APTES-modified nanosystems were found to be more efficient for PDT. An interesting photodynamic effect was observed in the case of TiO₂-APTES-Ce6 NPs. After illumination, the viability of U87 was decreased by 89% when they were exposed to 200 μg/mL of TiO₂-APTES-Ce6 NPs, which corresponds to 0.22 μM of Ce6. The same effect can be obtained with free photosensitizer but using a higher concentration of 10 μM of Ce6.

Enhanced photodynamic therapy using light fractionation against Streptococcus mutans biofilm: type I and type II mechanism

AIM

The objective of the study was to look the efficacy of fractionated light against Streptococcus mutans biofilm.

MATERIALS & METHODS

Antibiofilm assays (crystal violet, congo red), electron microscopic, confocal and spectroscopic studies were performed to check the effect of fractionated light.

RESULTS

6-6.5 log₁₀ reduction of planktonic and 3.6-4.2 log₁₀ reduction in biofilm were observed after irradiation with fractionated as compared with continuous light. Increased permeability to propidium iodide and leakage of cellular constituent validate the greater antibiofilm effect of fractionated light. Spectroscopic studies confirmed the relative contribution of type I and type II photochemistry.

CONCLUSION

Phenothiazinium dyes have a potential against bacterial biofilm in combination with light fractionation and it offers new opportunities to explore its clinical implication.

Photodynamic Therapy

Photodynamic therapy is a clinical technique for the treatment of cancers, microbial infections and other medical conditions by means of light-induced generation of reactive oxygen species using photosensitising drugs. The intrinsic fluorescence of many such drugs make them potential theranostic agents for simultaneous diagnosis and therapy. This chapter reviews the basic chemical and biological aspects of photodynamic therapy with an emphasis on its applications in theranostics. The roles of nanotechnology is highlighted, as well as emerging trends such as photoimmunotherapy, image-guided surgery and light- and singlet-oxygen dosimetry.

Use of Preservative Agents and Antibiotics for Increased Poliovirus Survival on Positively Charged Filters

Environmental surveillance of poliovirus (PV) and other non-enveloped viruses can help identify silent circulation and is necessary to certify eradication. The bag-mediated filtration system is an efficient method to filter large volumes of environmental waters at field sites for monitoring the presence of viruses. As filters may require long transit times to off-site laboratories for processing, viral inactivation or overgrowth of bacteria and fungi can interfere with virus detection and quantification (Miki and Jacquet in Aquatic Microb Ecol 51(2):195-208, 2008). To evaluate virus survival over time on ViroCap^™ filters, the filters were seeded with PV type 1 (PV1) and/or MS2 and then dosed with preservatives or antibiotics prior to storage and elution. These filters were stored at various temperatures and time periods, and then eluted for PV1 and MS2 recovery quantification. Filters dosed with the preservative combination of 2% sodium benzoate and 0.2% calcium propionate had increased virus survival over time when stored at 25 °C, compared to samples stored at 25 °C with no preservatives. While elution within 24 h of filtration is recommended, if storage or shipping is required then this preservative mixture can help preserve sample integrity. Addition of an antibiotic cocktail containing cephapirin, gentamicin, and Proclin^™ 300 increased recovery after storage at 4 and 25 °C, when compared to storage with no antibiotics. The antibiotic cocktail can aid sample preservation if access to appropriate antibiotics storage is available and sample cold chain is unreliable. This study demonstrated that the use of preservatives or antibiotics is a simple, cost-effective method to improve virus detection from ViroCap cartridge filters over time.

Potentiation of antimicrobial photodynamic inactivation by inorganic salts

INTRODUCTION

Antimicrobial photodynamic inactivation (aPDI) involves the use of non-toxic dyes excited with visible light to produce reactive oxygen species (ROS) that can destroy all classes of microorganisms including bacteria, fungi, parasites, and viruses. Selectivity of killing microbes over host mammalian cells allows this approach (antimicrobial photodynamic therapy, aPDT) to be used in vivo as an alternative therapeutic approach for localized infections especially those that are drug-resistant. Areas covered: We have discovered that aPDI can be potentiated (up to 6 logs of extra killing) by the addition of simple inorganic salts. The most powerful and versatile salt is potassium iodide, but potassium bromide, sodium thiocyanate, sodium azide and sodium nitrite also show potentiation. The mechanism of potentiation with iodide is likely to be singlet oxygen addition to iodide to form iodine radicals, hydrogen peroxide and molecular iodine. Another mechanism involves two-electron oxidation of iodide/bromide to form hypohalites. A third mechanism involves a one-electron oxidation of azide anion to form azide radical. Expert commentary: The addition of iodide has been shown to improve the performance of aPDT in several animal models of localized infection. KI is non-toxic and is an approved drug for antifungal therapy, so its transition to clinical use in aPDT should be straightforward.

Potentiation by potassium iodide reveals that the anionic porphyrin TPPS4 is a surprisingly effective photosensitizer for antimicrobial photodynamic inactivation

We recently reported that addition of the non-toxic salt, potassium iodide can potentiate antimicrobial photodynamic inactivation of a broad-spectrum of microorganisms, producing many extra logs of killing. If the photosensitizer (PS) can bind to the microbial cells, then delivering light in the presence of KI produces short-lived reactive iodine species, while if the cells are added after light the killing is caused by molecular iodine produced as a result of singlet oxygen-mediated oxidation of iodide. In an attempt to show the importance of PS-bacterial binding, we compared two charged porphyrins, TPPS4 (thought to be anionic and not able to bind to Gram-negative bacteria) and TMPyP4 (considered cationic and well able to bind to bacteria). As expected TPPS4+light did not kill Gram-negative Escherichia coli, but surprisingly when 100mM KI was added, it was highly effective (eradication at 200nM+10J/cm² of 415nm light). TPPS4 was more effective than TMPyP4 in eradicating the Gram-positive bacteria, methicillin-resistant Staphylococcus aureus and the fungal yeast Candida albicans (regardless of KI). TPPS4 was also highly active against E. coli after a centrifugation step when KI was added, suggesting that the supposedly anionic porphyrin bound to bacteria and Candida. This was confirmed by uptake experiments. We compared the phthalocyanine tetrasulfonate derivative (ClAlPCS4), which did not bind to bacteria or allow KI-mediated killing of E. coli after a spin, suggesting it was truly anionic. We conclude that TPPS4 behaves as if it has some cationic character in the presence of bacteria, which may be related to its delivery from suppliers in the form of a dihydrochloride salt.

Oral hygiene in intensive care unit patients with photodynamic therapy: study protocol for randomised controlled trial

BACKGROUND

In intensive care units (ICUs), nosocomial infections are prevalent conditions and they have been related to high mortality indexes. Some studies have suggested that inefficient oral hygiene and ventilator-associated pneumonia (VAP) are related. Nowadays, in the Brazilian public health system there is no well-defined protocol for oral hygiene in an ICU. Due to the drawbacks of the use of antibiotics, photodynamic therapy (PDT) has emerged as an interesting technique in order to reduce antimicrobial-resistant pathogens. Methylene blue (MB) is the most common chemical agent for PDT in Brazil. However, new formulations for improved effectiveness are still lacking. The objective of this study is to evaluate the use of an MB mouthwash as an effective oral-hygiene procedure in an ICU and to show that oral hygiene using PDT with MB mouthwash may reduce VAP frequency to rates similar to, or higher than, chlorhexidine.

METHODS

Phase 1 will evaluate the most effective cleaning procedure, while phase 2 will correlate oral hygiene to VAP incidence. At the start of phase 1, the ICU patients will be randomly allocated into three different groups (10 patients/group): the efficacy of chlorhexidine, classical MB-PDT, and mouthwash MB-PDT will all be measured for the quantification of viable bacteria, both pre- and post-treatment, by a Reverse Transcription Polymerase Chain Reaction (RT-PCR). In phase 2, the most effective procedure found in phase 1 and a mechanical cleaning with filtered water will be carried out daily, once a day, over 5 days, with a total of 52 ICU patients randomly allocated into the two groups. The clinical records will be evaluated in order to find any pneumonic diagnoses.

DISCUSSION

Since a variety of bacterial species are related to VAP, a universal primer for bacteria will be used in order to quantify the total bacteria count in the participants' samples. In order to quantify only the living bacteria before DNA extraction, the samples will be treated with propidium monoazide. This will infiltrate the dead bacteria and will intercalate the DNA bases, avoiding their DNA amplification. This will be the first trial to evaluate MB-PDT in a mouthwash formula that can increase the effectiveness due to the control of MB aggregation. The results of this study will be able to generate an easy and low-cost protocol to be used in an ICU for the Brazilian public health system.

TRIAL REGISTRATION

This protocol was approved by the Research Ethics Committee of the Conjunto Hospitalar do Mandaqui (1.317.834, CAAE: 49273515.9.3001.5551) and it was registered in Registro Brasileiro de Ensaios Clínicos (ReBEC number: RBR-94bvrc;). First received: 12 July 2015; 1st version 6 June 2016. Data will be published in a peer-reviewed journal.