Factors Determining the Susceptibility of Bacteria to Antibacterial Photodynamic Inactivation

Enhanced photocatalytic performance of colored Ti2O3-Ti3O5-TiO2 heterostructure for the degradation of antibiotic ofloxacin and bactericidal effect

Removing emergent contaminants, such as pharmaceuticals, and inhibiting bacteria by photocatalysis represents an interesting alternative for water remediation. We report the effective preparation of colored powders containing Ti2O3, Ti3O5, and TiO2, by a simple thermal oxidation reaction of a Ti2O3 precursor from 400 °C to 800 °C. The material obtained at 500 °C (P500 sample) exhibited the highest photocatalytic performance under simulated solar light, reaching 54% degradation of antibiotic ofloxacin and a bacteria inactivation of 51% and 62% for Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively. The superoxide anion radical was the main specie contributing to the photodegradation of ofloxacin, while the hydroxyl radical showed negligible effect. A synergy between the physicochemical properties of the phases in the P500 sample contributes to the electrons transfer, visible light absorption capability and generation of reactive oxygen species, resulting in its remarkable photoactivity. The comparison in terms of surface-specific activity revealed that the P500 sample is more efficient than commercially available TiO2 P25. This fact opens the option of using commercially available Ti2O3 and TiO2 P25 to obtain composites for promoting photoinduced reactions using natural solar light.

Can Porphyrin-Triphenylphosphonium Conjugates Enhance the Photosensitizer Performance Toward Bacterial Strains?

Antimicrobial photodynamic treatment (aPDT) offers an alternative option for combating microbial pathogens, and in this way, addressing the challenges of growing antimicrobial resistance. In this promising and effective approach, cationic porphyrins and related macrocycles have emerged as leading photosensitizers (PS) for aPDT. In general, their preparation occurs via N-alkylation of nitrogen-based moieties with alkyl halides, which limits the ability to fine-tune the features of porphyrin-based PS. Herein, is reported that the conjugation of porphyrin macrocycles with triphenylphosphonium units created a series of effective cationic porphyrin-based PS for aPDT. The presence of positive charges at both the porphyrin macrocycle and triphenylphosphonium moieties significantly enhances the photodynamic activity of porphyrin-based PS against both Gram-positive and Gram-negative bacterial strains. Moreover, bacterial photoinactivation is achieved with a notable reduction in irradiation time, exceeding 50%, compared to 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP), used as the reference and known as good PS. The improved capability of the porphyrin macrocycle to generate singlet oxygen combined with the enhanced membrane interaction promoted by the presence of triphenylphosphonium moieties represents a promising approach to developing porphyrin-based PS with enhanced photosensitizing activity.

Near-Infrared Light-Mediated Antibacterial Photodynamic Therapy Based on Erythrosine-Functionalized Mesoporous Silica-Coated Upconversion Nanoplatform

Infectious diseases caused by bacteria pose a serious threat to public health, and more worryingly, the unregulated application of antibiotics accelerates the emergence of bacterial resistance, presenting a major challenge to the effective treatment of infectious diseases caused by bacteria. Therefore, there is an urgent necessity to develop efficient and safe antimicrobial systems. Photodynamic therapy (PDT) is an attractive therapeutic approach that does not induce bacterial resistance. However, the clinical application of PDT has been limited by several factors, including the lower tissue penetration depth of photoactivation under visible light irradiation and the uncertain biosafety of photosensitizers (PS). This work presents an near infrared (NIR)-triggered core-shell upconversion nanoparticle-based PDT system composed of mesoporous silica-coated lanthanide-doped upconversion nanoparticles loaded with the photosensitizer erythrosine (UCSE). Upon NIR-triggering, erythrosine generates highly efficient reactive oxygen species that disrupt the cell membranes of Staphylococcus aureus and Escherichia coli, exhibiting a potent photodynamic antimicrobial effect. It is worth noting that the UCSE also exhibits excellent biosafety. In conclusion, we present an efficient NIR-triggered nanoantimicrobial system with excellent antimicrobial capacity and biosafety, which is a new therapeutic strategy for the control of bacterial infectious diseases.

Photoinactivation of Mycobacterium tuberculosis and Mycobacterium smegmatis by Near-Infrared Radiation Using a Trehalose-Conjugated Heptamethine Cyanine

The spread of multidrug-resistant mycobacterium strains requires the development of new approaches to combat diseases caused by these pathogens. For that, photodynamic inactivation (PDI) is a promising approach. In this study, a tricarbocyanine (TCC) is used for the first time as a near-infrared (740 nm) activatable PDI photosensitizer to kill mycobacteria with deep light penetration. For better targeting, a novel tricarbocyanine dye functionalized with two trehalose units (TCC2Tre) is developed. The photodynamic effect of the conjugates against mycobacteria, including Mycobacterium tuberculosis, is evaluated. Under irradiation, TCC2Tre causes more effective killing of mycobacteria compared to the photosensitizer without trehalose conjugation, with 99.99% dead vegetative cells of M. tuberculosis and M. smegmatis. In addition, effective photoinactivation of dormant forms of M. smegmatis is observed after incubation with TCC2Tre. Mycobacteria treated with TCC2Tre are more sensitive to 740 nm light than the Gram-positive Micrococcus luteus and the Gram-negative Escherichia coli. For the first time, this study demonstrates the proof of principle of in vitro PDI of mycobacteria including the fast-growing M. smegmatis and the slow-growing M. tuberculosis using near-infrared activatable photosensitizers conjugated with trehalose. These findings are useful for the development of new efficient alternatives to antibiotic therapy.

Reactive Oxygen Species (ROS)-Mediated Antibacterial Oxidative Therapies: Available Methods to Generate ROS and a Novel Option Proposal

The increasing emergence of multidrug-resistant (MDR) pathogens causes difficult-to-treat infections with long-term hospitalizations and a high incidence of death, thus representing a global public health problem. To manage MDR bacteria bugs, new antimicrobial strategies are necessary, and their introduction in practice is a daily challenge for scientists in the field. An extensively studied approach to treating MDR infections consists of inducing high levels of reactive oxygen species (ROS) by several methods. Although further clinical investigations are mandatory on the possible toxic effects of ROS on mammalian cells, clinical evaluations are extremely promising, and their topical use to treat infected wounds and ulcers, also in presence of biofilm, is already clinically approved. Biochar (BC) is a carbonaceous material obtained by pyrolysis of different vegetable and animal biomass feedstocks at 200-1000 °C in the limited presence of O2. Recently, it has been demonstrated that BC's capability of removing organic and inorganic xenobiotics is mainly due to the presence of persistent free radicals (PFRs), which can activate oxygen, H2O2, or persulfate in the presence or absence of transition metals by electron transfer, thus generating ROS, which in turn degrade pollutants by advanced oxidation processes (AOPs). In this context, the antibacterial effects of BC-containing PFRs have been demonstrated by some authors against Escherichia coli and Staphylococcus aureus, thus giving birth to our idea of the possible use of BC-derived PFRs as a novel method capable of inducing ROS generation for antimicrobial oxidative therapy. Here, the general aspects concerning ROS physiological and pathological production and regulation and the mechanism by which they could exert antimicrobial effects have been reviewed. The methods currently adopted to induce ROS production for antimicrobial oxidative therapy have been discussed. Finally, for the first time, BC-related PFRs have been proposed as a new source of ROS for antimicrobial therapy via AOPs.

Photodynamic therapy alone or in combination to counteract bacterial infections

INTRODUCTION

Antibacterial photodynamic therapy presents a promising alternative to antibiotics, with potential against multidrug-resistant bacteria, offering broad-spectrum action, reduced resistance risk, and improved tissue selectivity.

AREAS COVERED

This manuscript reviews patent literature in the field of antibacterial photodynamic therapy through the period of 2019-2023. All data are from the US and European patent databases and SciFinder.

EXPERT OPINION

Antibacterial photodynamic therapy (PDT) is an appealing approach for treating bacterial infections, especially biofilm-related ones, by releasing reactive oxygen species (ROS) upon light activation. Its success is driven by a growing variety of photosensitizers (PSs) with tailored properties, like water solubility, controllable surface charge, and ROS generation efficiency. Among them, Aggregation Induced Emission (AIE)-type PSs are promising, demonstrating enhanced efficacy when aggregated in biological environments. However, the penetration of pristine PSs into bacterial biofilms within deep tissues or complex anatomical regions is limited, reducing their antibacterial effectiveness. To address this, nanotechnology has been integrated into antibacterial PDT to synthesize various nano-PSs. This adaptability allows seamless integration with other antimicrobial treatments, offering a comprehensive approach to combat localized infections, especially in dentistry and dermatology. By combining PSs with complementary therapies, antibacterial PDT offers a multifaceted strategy for effective microbial control and management.

TMPyP-mediated photoinactivation of Pseudomonas aeruginosa improved in the presence of a cationic polymer

Pseudomonas aeruginosa is one of the most refractory organisms to antibiotic treatment and appears to be one of the least susceptible to photodynamic treatment. TMPyP is effective in the photoinactivation of P. aeruginosa, and the co-administration with the cationic polymer Eudragit®-E100 (Eu) potentiates this effect against isolates both sensitive and resistant to antibiotics. The fluorescent population (>98%) observed by flow cytometry after exposure to Eu + TMPyP remained unchanged after successive washings, indicating a stronger interaction/internalization of TMPyP in the bacteria, which could be attributed to the rapid neutralization of surface charges. TMPyP and Eu produced depolarization of the cytoplasmic membrane, which increased when both cationic compounds were combined. Using confocal laser scanning microscopy, heterogeneously distributed fluorescent areas were observed after TMPyP exposure, while homogeneous fluorescence and enhanced intensity were observed with Eu + TMPyP. The polymer caused alterations in the bacterial envelopes that contributed to a deeper and more homogeneous interaction/internalization of TMPyP, leading to a higher probability of damage by cytotoxic ROS and explaining the enhanced result of photodynamic inactivation. Therefore, Eu acts as an adjuvant without being by itself capable of eradicating this pathogen. Moreover, compared with other therapies, this combinatorial strategy with a polymer approved for pharmaceutical applications presents advantages in terms of toxicity risks.

Potential of using medicinal plant extracts as photosensitizers for antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (APDT) is a promising approach to overcome antimicrobial resistance. However, for widespread implementation of this approach, approved photosensitizers are needed. In this study, we used commercially available preparations (Calendulae officinalis floridis extract, Chamomillae recutitae floridis extract, Achillea millefolii herbae extract; Hypericum perforatum extract; Eucalyptus viminalis folia extract) as photosensitizers for inactivation of gram-negative (Pseudomonas aeruginosa) and gram-positive (Staphylococcus aureus) bacteria. Spectral-luminescent analysis has shown that the major chromophores are of chlorophyll (mainly chlorophyll a and b) and hypericin nature. The extracts are efficient generators of singlet oxygen with quantum yield (γΔ ) from 0.40 to 0.64 (reference compound, methylene blue with γΔ = 0.52). In APDT assays, bacteria before irradiation were incubated with extracts for 30 min. After irradiation and 24 h of incubation, colony-forming units (CFU) were counted. Upon exposure of P. aeruginosa to radiation of 405 nm, 590 nm, and 660 nm at equal energy dose of 30 J/cm2 (irradiance - 100 mW/cm2 , exposure time - 5 min), the most pronounced effect is observed with blue light (>3 log10 reduction); in case of S. aureus, the effect is approximately equivalent for light of indicated wavelengths and dose (>4 log10 reduction).

Effects of antimicrobial photodynamic therapy with photodithazine® on methicillin-resistant Staphylococcus aureus (MRSA): Studies in biofilms and experimental model with Galleria mellonella

Staphylococcus aureus infections are a severe health problem due to the high mortality rate. Conventional treatment of these infections is via the administration of antibiotics. However, its indiscriminate use can select resistant microorganisms. Thus, it is necessary to develop alternatives for antibiotic therapy. Antimicrobial Photodynamic Therapy (aPDT), a therapeutic method that associates a photosensitizer (PS), a light source with adequate wavelength to the PS, interacts with molecular oxygen generating reactive oxygen species responsible for cell inactivation, is a viable alternative. This work aimed to analyze, in vitro and in vivo, the action of aPDT with PS Photodithazine® (PDZ) on the methicillin-resistant S. aureus (MRSA) strain. In the in vitro method, the S. aureus biofilm was incubated with PDZ at 50 and 75 μg.mL-1 for 15 min, adopting the light dose of 25, 50, and 100 J/cm2. In addition, PS interaction, formation of reactive oxygen species (ROS), bacterial metabolism, adhesion, bacterial viability, and biofilm structure were evaluated by scanning electron microscopy. Subsequently, the strain was inoculated into models of Galleria mellonella, and the survival curve, health scale, blood cell analysis, and CFU/mL of S. aureus in the hemolymph were analyzed after aPDT. In the in vitro results, bacterial reduction was observed in the different PDZ concentrations, highlighting the parameters of 75 μg.mL-1 of PDZ and 100 J/cm2. As for in vivo results, aPDT increased survival and stimulated the immune system of G. mellonella infected by S. aureus. aPDT proved effective in both models, demonstrating its potential as an alternative therapy in treating MRSA bacterial infections.

Refining antimicrobial photodynamic therapy: effect of charge distribution and central metal ion in fluorinated porphyrins on effective control of planktonic and biofilm bacterial forms

Antibiotic resistance represents a pressing global health challenge, now acknowledged as a critical concern within the framework of One Health. Photodynamic inactivation of microorganisms (PDI) offers an attractive, non-invasive approach known for its flexibility, independence from microbial resistance patterns, broad-spectrum efficacy, and minimal risk of inducing resistance. Various photosensitizers, including porphyrin derivatives have been explored for pathogen eradication. In this context, we present the synthesis, spectroscopic and photophysical characteristics as well as antimicrobial properties of a palladium(II)-porphyrin derivative (PdF2POH), along with its zinc(II)- and free-base counterparts (ZnF2POH and F2POH, respectively). Our findings reveal that the palladium(II)-porphyrin complex can be classified as an excellent generator of reactive oxygen species (ROS), encompassing both singlet oxygen (Φ△ = 0.93) and oxygen-centered radicals. The ability of photosensitizers to generate ROS was assessed using a variety of direct (luminescence measurements) and indirect techniques, including specific fluorescent probes both in solution and in microorganisms during the PDI procedure. We investigated the PDI efficacy of F2POH, ZnF2POH, and PdF2POH against both Gram-negative and Gram-positive bacteria. All tested compounds proved high activity against Gram-positive species, with PdF2POH exhibiting superior efficacy, leading to up to a 6-log reduction in S. aureus viability. Notably, PdF2POH-mediated PDI displayed remarkable effectiveness against S. aureus biofilm, a challenging target due to its complex structure and increased resistance to conventional treatments. Furthermore, our results show that PDI with PdF2POH is more selective for bacterial than for mammalian cells, particularly at lower light doses (up to 5 J/cm2 of blue light illumination). This enhanced efficacy of PdF2POH-mediated PDI as compared to ZnF2POH and F2POH can be attributed to more pronounced ROS generation by palladium derivative via both types of photochemical mechanisms (high yields of singlet oxygen generation as well as oxygen-centered radicals). Additionally, PDI proved effective in eliminating bacteria within S. aureus-infected human keratinocytes, inhibiting infection progression while preserving the viability and integrity of infected HaCaT cells. These findings underscore the potential of metalloporphyrins, particularly the Pd(II)-porphyrin complex, as promising photosensitizers for PDI in various bacterial infections, warranting further investigation in advanced infection models.

Conjugated polymer nanoparticles as sonosensitizers in sono-inactivation of a broad spectrum of pathogens

Sonodynamic inactivation (SDI) of pathogens has an important advantage when compared to optical excitation-based protocols due to the deeper penetration of ultrasound (US) excitation in biological media or animal tissue. Sonosensitizers (SS) are compounds or systems that upon US stimulation in the therapeutic window (frequency = 0.8-3 MHz and intensity < 3 W/cm2) can induce damage to vital components of pathogenic microorganisms. Herein, we report the synthesis and application of conjugated polymer nanoparticles (CPNs) as an efficient SS in SDI of methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae and Candida tropicalis. A frequent problem in the design and testing of new SS for SDI is the lack of proper sonoreactor characterization which leads to reproducibility concerns. To address this issue, we performed dosimetry experiments in our setup. This enables the validation of our results by other researchers and facilitates meaningful comparisons with different SDI systems in future studies. On a different note, it is generally accepted that the mechanisms of action underlying SS-mediated SDI involve the production of reactive oxygen species (ROS). In an attempt to establish the nature of the cytotoxic species involved in our CPNs-based SDI protocol, we demonstrated that singlet oxygen (1O2) does not play a major role in the observed sonoinduced killing effect. SDI experiments in planktonic cultures of optimally growing pathogens using CPNs result in a germicide effect on the studied pathogenic microorganisms. The implementation of SDI protocols using CPNs was further tested in mature biofilms of a MRSA resulting in ∼40 % reduction of biomass and ∼70 % reduction of cellular viability. Overall, these results highlight the unique and unexplored capacity of CPNs to act as sonosensitizers opening new possibilities in the design and application of novel inactivation protocols against morbific microbes.

Increasing the Selectivity of Light-Active Antimicrobial Agents - Or How To Get a Photosensitizer to the Desired Target

Photosensitizers combine the inherent reactivity of reactive oxygen species with the sophisticated reaction control of light. Through selective targeting, these light-active molecules have the potential to overcome certain limitations in drug discovery. Ongoing advances in the synthesis and evaluation of photosensitizer conjugates with biomolecules such as antibodies, peptides, or small-molecule drugs are leading to increasingly powerful agents for the eradication of a growing number of microbial species. This review article, therefore, summarizes challenges and opportunities in the development of selective photosensitizers and their conjugates described in recent literature. This provides adequate insight for newcomers and those interested in this field.

Photoinactivation and Photoablation of Porphyromonas gingivalis

Several types of phototherapy target human pathogens and Porphyromonas gingivitis (Pg) in particular. The various approaches can be organized into five different treatment modes sorted by different power densities, interaction times, effective wavelengths and mechanisms of action. Mode 1: antimicrobial ultraviolet (aUV); mode 2: antimicrobial blue light (aBL); mode 3: antimicrobial selective photothermolysis (aSP); mode 4: antimicrobial vaporization; mode 5: antimicrobial photodynamic therapy (aPDT). This report reviews the literature to identify for each mode (a) the putative molecular mechanism of action; (b) the effective wavelength range and penetration depth; (c) selectivity; (d) in vitro outcomes; and (e) clinical trial/study outcomes as these elements apply to Porphyromonas gingivalis (Pg). The characteristics of each mode influence how each is translated into the clinic.

Antimicrobial Resistance: Is There a 'Light' at the End of the Tunnel?

In recent years, with the increases in microorganisms that express a multitude of antimicrobial resistance (AMR) mechanisms, the threat of antimicrobial resistance in the global population has reached critical levels. The introduction of the COVID-19 pandemic has further contributed to the influx of infections caused by multidrug-resistant organisms (MDROs), which has placed significant pressure on healthcare systems. For over a century, the potential for light-based approaches targeted at combatting both cancer and infectious diseases has been proposed. They offer effective killing of microbial pathogens, regardless of AMR status, and have not typically been associated with high propensities of resistance development. To that end, the goal of this review is to describe the different mechanisms that drive AMR, including intrinsic, phenotypic, and acquired resistance mechanisms. Additionally, the different light-based approaches, including antimicrobial photodynamic therapy (aPDT), antimicrobial blue light (aBL), and ultraviolet (UV) light, will be discussed as potential alternatives or adjunct therapies with conventional antimicrobials. Lastly, we will evaluate the feasibility and requirements associated with integration of light-based approaches into the clinical pipeline.

Preclinical Studies on the Safety and Toxicity of Photoditazine in the Antibacterial Photodynamic Therapy of Uropathogenic Bacteria

The 'dusting' technique of lithotripsy for the removal of infected urinary calculi and the wide use of drainage after endoscopic surgery may stimulate spreading of multidrug-resistant bacterial strains. Antibacterial photodynamic therapy (PDT) is one promising method for the elimination these strains. The purpose of our study was to evaluate alterations of renal pelvis morphology and renal function in laboratory animals after bactericidal regimens of PDT. Renal pelvises of pigs were filled with Photoditazine and then assessed either by examining the accumulation of Photoditazine in the urothelium or by illumination with a laser at a wavelength of 662 nm. A renal test and a complete blood count was performed to assess a negative effect of the treatment on health. Structural alterations of the kidney tissues were analyzed by histological examination. No photosensitizer fluorescence was detected in the urothelium of the pelvis. Histological study showed that PDT caused minor changes to the urothelium of the renal pelvis but did not affect the underlying connective tissue. No renal function abnormalities were found after PDT. Thus, the study indicates that antibacterial PDT is a safety technique that can complement common antibiotic therapy in the surgical treatment of urolithiasis.

Photodynamic Activity of Chlorophyllin and Polyethylenimine on Pseudomonas aeruginosa Planktonic, Biofilm and Persister Cells

Antimicrobial photodynamic inactivation is considered a promising antimicrobial approach that may not develop resistance in the near future. Here, we investigate the influence of the photosensitizer chlorophyllin (CHL) and the cationic permeabilizer polyethylenimine (PEI), exposed to a red light-emitting diode, on the human pathogen Pseudomonas aeruginosa free-living planktonic cells, the sessile biofilm and persister cells. The broth microdilution checkerboard method was used to test antimicrobial susceptibility. As a substrate for biofilms, the Calgary biofilm device was used, and the quantification of the biofilm biomass was carried out using a crystal violet assay. Serine hydroxamate was used for the induction of persisters. Our findings reveal that PEI ameliorates the antimicrobial activity of CHL against P. aeruginosa planktonic and biofilm states, and the concentration required to eradicate the bacteria in the biofilm is more than fourfold that is required to eradicate planktonic cells. Interestingly, the persister cells are more susceptible to CHL/PEI (31.25/100 µg mL-1) than the growing cells by 1.7 ± 0.12 and 0.4 ± 0.1 log10 reduction, respectively, after 15 min of illumination. These data demonstrate that CHL excited with red light together with PEI is promising for the eradication of P. aeruginosa, and the susceptibility of P. aeruginosa to CHL/PEI is influenced by the concentrations and the exposure time.

Recent Progress in the Characterization, Synthesis, Delivery Procedures, Treatment Strategies, and Precision of Antimicrobial Peptides

Infectious diseases are constantly evolving to bypass antibiotics or create resistance against them. There is a piercing alarm for the need to improve the design of new effective antimicrobial agents such as antimicrobial peptides which are less prone to resistance and possess high sensitivity. This would guard public health in combating and overcoming stubborn pathogens and mitigate incurable diseases; however, the emergence of antimicrobial peptides' shortcomings ranging from untimely degradation by enzymes to difficulty in the design against specific targets is a major bottleneck in achieving these objectives. This review is aimed at highlighting the recent progress in antimicrobial peptide development in the area of nanotechnology-based delivery, selectivity indices, synthesis and characterization, their doping and coating, and the shortfall of these approaches. This review will raise awareness of antimicrobial peptides as prospective therapeutic agents in the medical and pharmaceutical industries, such as the sensitive treatment of diseases and their utilization. The knowledge from this development would guide the future design of these novel peptides and allow the development of highly specific, sensitive, and accurate antimicrobial peptides to initiate treatment regimens in patients to enable them to have accommodating lifestyles.

The Parameters Affecting Antimicrobial Efficiency of Antimicrobial Blue Light Therapy: A Review and Prospect

Antimicrobial blue light (aBL) therapy is a novel non-antibiotic antimicrobial approach which works by generating reactive oxygen species. It has shown excellent antimicrobial ability to various microbial pathogens in many studies. However, due to the variability of aBL parameters (e.g., wavelength, dose), there are differences in the antimicrobial effect across different studies, which makes it difficult to form treatment plans for clinical and industrial application. In this review, we summarize research on aBL from the last six years to provide suggestions for clinical and industrial settings. Furthermore, we discuss the damage mechanism and protection mechanism of aBL therapy, and provide a prospect about valuable research fields related to aBL therapy.

Influence of Contemporary Photoactivated Disinfection on the Mechanical Properties and Antimicrobial Activity of PMMA Denture Base: A Systematic Review and Meta Analysis

PURPOSE

The present study aimed to perform a systematic review and meta-analysis to investigate the effectiveness of the contemporary photoactivated disinfection methods on the mechanical features and/or antimicrobial activity of polymethyl methacrylate (PMMA) dentures bases.

METHODS

THE FOCUSED RESEARCH QUESTION WAS: : "What is the effect of contemporary photoactivated disinfection methods as compared to conventional disinfection protocols on the mechanical features and/or antimicrobial activity of PMMA dentures bases?". An electronic literature search was carried out by the author and a senior librarian specialized in health sciences on Web of Science, PubMed, and Scopus. In vitro investigations evaluating the antimicrobial and/or mechanical effects of photoactivated disinfectants as compared to conventional chemical disinfectants on the microbes formed on PMMA denture bases were included. Meta-analysis was performed for calculating the standard mean difference (SMD) with a 95% confidence interval.

RESULTS

Four out of eight studies concluded that photoactivated disinfectants, including riboflavin-mediated photodynamic therapy (PDT), hematoporphyrin-mediated PDT, poly-L-glycolic acid loaded with methylene blue, Erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser, erbium-doped yttrium-aluminum-garnet (Er:YAG) laser, and chitosan-mediated PDT, demonstrated a significant reduction in colony-forming unit per milliliter (CFU/mL) of exposed viable colonies of Escherichia coli (E. coli), Streptococcus mutans (S. mutans), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans) comparable to the conventionally used chemical disinfectants of PMMA denture bases. Contrarily, two studies concluded that the PMMA denture base colonized with C. albicans and disinfected with conventional chemical disinfectants showed the greatest anti-fungal efficaciousness. All the included studies concluded that the application of photoactivated disinfectants does not negatively impact the mechanical features of the PMMA denture bases colonized with microbes including E. coli, S. mutans, S. aureus, and C. albicans. The meta-analysis revealed statistically significant reduction in C. albicans counts (CFU/mL [Log10]) (p < 0.00001) and improvement in the flexural strength (p = 0.0002) of PMMA-based denture base after the application of conventional disinfectants, while a statistically significant improvement in the fracture strength of PMMA-based denture base was observed after the application of photoactivated disinfectants (p = 0.03).

CONCLUSION

According to the systematic review (qualitative synthesis), photoactivated disinfectants demonstrated comparable mechanical features and antimicrobial activity of PMMA dentures bases to conventional chemical disinfectants suggesting their potential to be utilized as an alternative to conventional chemical disinfectants. However, the meta-analysis (quantitative synthesis) revealed that the application of conventional disinfectants demonstrated better outcomes related to antimicrobial activity and flexural strength of PMMA-based denture based.

Antimicrobial phyto-photodynamic activity inducing by polyphenol-supported Methylene Blue co-loaded into multifunctional bilosomes: Advanced hybrid nanoplatform in the skin infections treatment?

Widespread skin infections caused primarily by bacteria and yeast, pose a growing threat to healthcare systems. Phyto-photodynamic antimicrobial therapy is a promising treatment strategy with a few mild side effects for both superficial and deeper skin infections. The combination of natural plant products (polyphenols) with conventional photosensitizers makes it possible to improve the outcome of skin infections. In the present study, nanoengineered self-assembling bilosomes were used as a nanoplatform to deliver two compounds with different solubility, i.e., curcumin applied as a hydrophobic phytochemical compound and Methylene Blue used as a hydrophilic photosensitizer. Compared with the encapsulation of Methylene Blue alone, the double-loaded bilosomes (curcumin-supported Methylene Blue) showed higher efficiency in generating reactive oxygen species. Importantly, in our study, we also confirmed that bioinspired bilosomes prevent the rapid photobleaching of Methylene Blue, thereby enhancing its photoactivity. The post-irradiation antimicrobial action was tested against two pathogens - the Gram-positive bacterium (Staphylococcus aureus) and yeast (Candida albicans). The irradiation was provided after 10, 20, and 30 min, at a specific wavelength (λ = 640 nm) corresponding to 63, 126, and 189 J cm^-2 energy fluences. The most effective reduction in the microbial cells number was found 30 min post-irradiation and was 99.994% for double-loaded bilosomes compared to 99.989% killing S. aureus for bilosomes with Methylene Blue alone. For C. albicans fungal cells, the mortality was 99.669% in the presence of a Methylene Blue and curcumin mixture compared to 98.229% of those killed without the addition of curcumin. The overall results of our contribution provide evidence that curcumin in combination with MB enhances the photo-eradication efficiency of S. aureus and C. albicans planktonic cultures. Thus, the mixture of the phytochemicals with photosensitizers and their encapsulation in multifunctional bilosomes may contribute to the development of innovative antimicrobial phyto-photodynamic therapy in the future.

Antimicrobial photodynamic inactivation as an alternative approach to inhibit the growth of Cronobacter sakazakii by fine-tuning the activity of CpxRA two-component system

Cronobacter sakazakii is an opportunistic foodborne pathogen primarily found in powdered infant formula (PIF). To date, it remains challenging to control the growth of this ubiquitous bacterium. Herein, antimicrobial photodynamic inactivation (aPDI) was first employed to inactivate C. sakazakii. Through 460 nm light irradiation coupled with hypocrellin B, the survival rate of C. sakazakii was diminished by 3~4 log. The photokilling effect was mediated by the attenuated membrane integrity, as evidenced by PI staining. Besides, scanning electron microscopy showed the deformed and aggregated cell cluster, and intracellular ROS was augmented by 2~3 folds when light doses increase. In addition to planktonic cells, the biofilm formation of C. sakazakii was also affected, showing an OD_590nm decline from 0.85 to 0.25. In terms of molecular aspects, a two-component system called CpxRA, along with their target genes, was deregulated during illumination. Using the knock-out strain of ΔCpxA, the bacterial viability was reduced by 2 log under aPDI, a wider gap than the wildtype strain. Based on the promoted expression of CpxR and OmpC, aPDI is likely to play its part through attenuating the function of CpxRA-OmpC pathway. Finally, the aPDI system was applied to PIF, and C. sakazakii was inactivated under various desiccated or heated storage conditions. Collectively, aPDI serves as an alternative approach to decontaminate C. sakazakii, providing a new strategy to reduce the health risks caused by this prevalent foodborne pathogen.

Priming effect with photoinactivation against extensively drug-resistant Enterobacter cloacae and Klebsiella pneumoniae

In this study, we present antimicrobial blue light (aBL) and antimicrobial photoinactivation with green light in the presence of Rose Bengal (aPDI) to modulate the susceptibility of extensively drug-resistant (XDR) Enterobacter cloacae and Klebsiella pneumoniae clinical isolates to antimicrobials. This process can be considered a photodynamic priming tool that influences other therapeutic options, such as antibiotics. The current study evaluated the different environments to estimate the most effective priming conditions by testing a broad spectrum of antimicrobials (including antimicrobials with different targets and mechanisms of action). The susceptibility of the E. cloacae and K. pneumoniae clinical isolates to various antibiotics after aBL and green light (with rose bengal) as aPDI treatment was examined with multiple methods of synergy testing (e.g., diffusion methods, checkerboard assay, postantibiotic effect), and most effective photoinactivation conditions were implemented for each environment. When Enterobacteriaceae were exposed to aBL, the most efficient reduction in survival rate under TSB conditions was observed. Similar results were observed when rose bengal, as a photosensitizer, was present during the exposure to green light in PBS. aBL and aPDI led to an increased susceptibility of K. pneumoniae and E. cloacae isolates to chloramphenicol and colistin or fosfomycin and colistin antibiotics, respectively. However, among the 4 tested isolates, we observed synergies between different antimicrobial agents and photoinactivation conditions. Thus, it may suggest that the sensitization process may be considered a strain dependent priming tool.

Antibacterial and Antibiofilm Potency of Menadione Against Multidrug-Resistant S. aureus

Menadione is an analogue of 1,4-naphthoquinone (1,4-NQ) that possesses enormous pharmaceutical potential. The minimum inhibitory concentration (MIC) of menadione was determined against eighteen pathogens of the ESKAPE category, including thirteen multidrug-resistant (MDR) and five standard strains. From a total of eighteen pathogens, five strains of S. aureus (four: MDR and one: Standard strain) were considered further for detailed studies. This study included the determination of minimum bactericidal concentration (MBC), time-kill assay, scanning electron microscopic technique (SEM), and detection of reactive oxygen species (ROS). Additionally, the effect of menadione on biofilms of three strains of S. aureus was performed through crystal violet assay, SEM, and confocal laser scanning microscopy (CLSM). Menadione exerted substantial antibacterial activity against S. aureus (S8, S9, NCIM 5021) at a lower MIC (64 µg/mL). Whereas, the MIC of 256 µg/mL was displayed against J2 and J4 (MDR and biofilm-forming strains). The time-killing effect of menadione against S. aureus strains was observed after 9 h at MBCs of 64 µg/mL (NCIM 5021), 128 µg/mL (S8, S9), and 512 µg/mL (J2, J4). Enhanced levels of ROS in all five S. aureus were observed in presence of menadione (MICs and MBCs). The relation of enhanced ROS due to menadione activity invigorated us to explore its effect on S. aureus biofilms. We report menadione-mediated inhibition (> 90%) of biofilm formation (at respective MICs) and effect on preformed biofilms (> 85%) at 1024 µg/mL. Menadione possessing antibacterial and antibiofilm potentials are imperative in the era of multidrug resistance developed by bacterial pathogens.

Evaluation of photosensitizer-containing superhydrophobic surfaces for the antibacterial treatment of periodontal biofilms

Antimicrobial photodynamic therapy (aPDT) is a promising approach to control biofilms involved in periodontal diseases. However, certain challenges, such as staining of teeth, preferential interaction of photosensitizer (PS) with Gram-positive versus Gram-negative bacteria, and insufficient oxygen in hypoxic periodontal pockets have presented barriers to its use in the clinic. To overcome these challenges, a novel superhydrophobic (SH) film that generates airborne singlet oxygen has been developed. The SH-aPDT approach isolates the PS onto a topologically rough solid SH film on which channels allow air to diffuse to the PS surface, thus ensuring sufficient oxygen supply. Upon illumination, gas phase singlet oxygen (¹O₂) is produced and diffuses from the SH surface to the underlying biofilm. The killing efficacy was assessed as a function of transmitted fluence (17.9-89.5 J/cm²) and chorin e6 loading (96-1110 nmol/cm²) by counting of colony forming units, biofilm metabolism by XTT and confocal microscopy. The decrease in viability of both Gram-positive and Gram-negative bacteria in a multi-species biofilm was found to be linearly dependent on the fluence as well as the loading of the PS up to 71.6 J/cm² when 1110 nmols/cm² of chlorin e6 was used. A > 4.6 log bacterial reduction was observed under these conditions (p < 0.05). This novel SH-aPDT approach shows promise as an effective method to disinfect multi-species bacterial biofilms associated with periodontal disease and will be evaluated in animal models in future studies.

Photodynamic inactivation of pathogenic Gram-negative and Gram-positive bacteria mediated by Si(IV) phthalocyanines bearing axial ammonium units

The photodynamic inactivation (PDI) of microorganisms has gained interest as an efficient option for conventional antibiotic treatments. Recently, Si(IV) phthalocyanines (SiPcs) have been highlighted as promising photosensitizers (PSs) to the PDI of microorganisms due to their remarkable absorption and emission features. To increase the potential of cationic SiPcs as PS drugs, one novel (1a) and two previously described (2a and 3a) axially substituted PSs with di-, tetra-, and hexa-ammonium units, respectively, were synthesized and characterized. Their PDI effect was evaluated for the first time against Escherichia coli and Staphylococcus aureus, a Gram-negative and a Gram-positive bacterium, respectively. The photodynamic treatments were conducted with PS concentrations of 3.0 and 6.0 μM under 60 min of white light irradiation (150 mW.cm^-2). The biological results show high photodynamic efficiency for di- and tetra-cationic PSs 1a and 2a (6.0 μM), reducing the E. coli viability in 5.2 and 3.9 log, respectively (after 15 min of dark incubation before irradiation). For PS 3a, a similar bacterial reduction (3.6 log) was achieved but only with an extended dark incubation period (30 min). Under the same experimental conditions, the photodynamic effect of cationic PSs 1a-3a on S. aureus was even more promising, with abundance reductions of ca. 8.0 log after 45-60 min of PDI treatment. These results reveal the high PDI efficiency of PSs bearing ammonium groups and suggest their promising application as a broad-spectrum antimicrobial to control infections caused by Gram-negative and Gram-positive bacteria.

Application of Fullerenes as Photosensitizers for Antimicrobial Photodynamic Inactivation: A Review

Antimicrobial photodynamic inactivation (aPDI) is a newly emerged treatment approach that can effectively address the issue of multidrug resistance resulting from the overuse of antibiotics. Fullerenes can be used as promising photosensitizers (PSs) for aPDI due to the advantages of high triplet state yields, good photostability, wide antibacterial spectrum, and permissibility of versatile functionalization. This review introduces the photodynamic activities of fullerenes and the up-to-date understanding of the antibacterial mechanisms of fullerene-based aPDI. The most recent works on the functionalization of fullerenes and the application of fullerene derivatives as PSs for aPDI are also summarized. Finally, certain remaining challenges are emphasized to provide guidance on future research directions for achieving clinical application of fullerene-based aPDI.

Charge effect of water-soluble porphyrin derivatives as a prototype to fight infections caused by Acinetobacter baumannii by aPDT approaches

In the last decade, Acinetobacter baumannii has emerged as a pathogen associated with infections in intensive care units worldwide, especially due to its ability to resist an extensive list of antibiotics. In this context, porphyrins have emerged as an important strategy in photodynamic therapy, since they are a group of tetrapyrrolic compounds with important photochemical and photobiological activities. In this study, the antimicrobial photodynamic activity of meso-tetra(4-N-methyl-pyridyl)porphyrin (H₂TMePyP⁺) and meso-tetra(4-sulfonatophenyl)porphyrin (H₂TPPS^‒) was evaluated against A. baumannii by minimum inhibitory concentration (MIC), anti-biofilm activity, and the interaction with antibiotics after exposure to white-light LED irradiation. The cationic derivative H₂TMePyP⁺ was more potent (MIC = 0.61 µM) than H₂TPPS^‒, with anti-biofilm activity and increased the antimicrobial activity of ciprofloxacin and amikacin. Given these findings, the tetra-cationic porphyrins can be assumed as prototypes to optimize and develop new agents by promoting oxidative stress and inducing free radical production.

Gallium Mesoporphyrin IX-Mediated Photodestruction: A Pharmacological Trojan Horse Strategy To Eliminate Multidrug-Resistant Staphylococcus aureus

One of the factors determining efficient antimicrobial photodynamic inactivation (aPDI) is the accumulation of a light-activated compound, namely, a photosensitizer (PS). Targeted PS recognition is the approach based on the interaction between the membrane receptor on the bacterial surface and the PS, whereas the compound is efficiently accumulated by the same mechanism as the natural ligand. In this study, we showed that gallium mesoporphyrin IX (Ga³⁺MPIX) provided dual functionality—iron metabolism disruption and PS properties in aPDI. Ga³⁺MPIX induced efficient (>5log₁₀ reduction in CFU/mL) bacterial photodestruction with excitation in the area of Q band absorption with relatively low eukaryotic cytotoxicity and phototoxicity. The Ga³⁺MPIX is recognized by the same systems as haem by the iron-regulated surface determinant (Isd). However, the impairment in the ATPase of the haem detoxification efflux pump was the most sensitive to the Ga³⁺MPIX-mediated aPDI phenotype. This indicates that changes within the metalloporphyrin structure (vinyl vs ethyl groups) did not significantly alter the properties of recognition of the compound but influenced its biophysical properties.

Recent advances in nanoparticle-based targeting tactics for antibacterial photodynamic therapy

Abstract

The rise of antibacterial drug resistance means treatment options are becoming increasingly limited. We must find ways to tackle these hard-to-treat drug-resistant and biofilm infections. With the lack of new antibacterial drugs (such as antibiotics) reaching the clinics, research has switched focus to exploring alternative strategies. One such strategy is antibacterial photodynamic therapy (aPDT), a system that relies on light, oxygen, and a non-toxic dye (photosensitiser) to generate cytotoxic reactive oxygen species. This technique has already been shown capable of handling both drug-resistant and biofilm infections but has limited clinical approval to date, which is in part due to the low bioavailability and selectivity of hydrophobic photosensitisers. Nanotechnology-based techniques have the potential to address the limitations of current aPDT, as already well-documented in anti-cancer PDT. Here, we review recent advances in nanoparticle-based targeting tactics for aPDT.

Graphical Abstract

Disinfection efficacy and fracture strength of PMMA denture-based polymer with chlorhexidine, PDT utilizing Rose Bengal and hematoporphyrin, and Er, Cr: YSGG laser

OBJECTIVE

The study aimed to assess and compare disinfection efficacy and fracture strength of PMMA based DBPs using chlorhexidine (CHX), PDT utilizing Rose Bengal (RB) and hematoporphyrin HPD, and Er,Cr:YSGG laser (ECL) induced antimicrobial action against in-vitro biofilms colonized with C.albicans, S.aureus, S. mutans, and E. coli.

MATERIAL AND METHODS

American Type Culture Collection (ATCC) of C.albicans, S.aureus, S. mutans and E. coli were cultured. Forty-eight PMMA-based denture base plates (DBPs) were prepared by heat-cure acrylic resin and contaminated by in-vitro biofilm under-stimulated in-vitro conditions. DBPs were treated with group1; ECL group 2; RB 5µm, group 3; HPD 500 mg/L and group 4; 0.12% CHX (controls) respectively, for the disinfection of biofilms. All photosensitizers (PS) were activated by LED at a different wavelength. Each contaminated DBP was sprayed on all its surfaces with the aforementioned photosensitizers and CHX. One-way analysis of variance (ANOVA) was used to test the efficacy of disinfection and fracture load testing. Tukey multiple comparison tests were performed to compare means of CFU/mL (log10) for exposed E. coli, C. albicans, S aureus, and S. mutans.

RESULTS

Specimens in group 1 disinfected with erbium laser, group 3 disinfected with HPD, and group 4 sterilized with chemical disinfection were effective in decreasing bacterial load CFU/mL (log10) against C.albicans, S. aureus, S.mutans, and E. Coli (p>0.05). Intergroup comparison demonstrated ECL, CHX and HPD demonstrated a comparable reduction against C.albicans and S.aureus (p>0.05). Similarly, S.mutans and E.coli were sensitive against all experimental groups (p>0.05). no significant difference in fractural load analysis among the different investigated groups was noted (p>0.05).

CONCLUSION

ECL and HPD photosensitizer revealed a significant reduction in CFU/ml of exposed viable colonies of C.albicans, S.aureus, S. mutans, and E. coli comparable to 0.12% CHX mediated disinfection of PMMA-based DBPs. Irrespective of the type of disinfection no influence of disinfection was noted on the fracture load of PMMA DBPs.

Photodynamic Inactivation of Antibiotic-Resistant and Sensitive Aeromonas hydrophila with Peripheral Pd(II)- vs. Zn(II)-Phthalocyanines

The antimicrobial multidrug resistance (AMR) of pathogenic bacteria towards currently used antibiotics has a remarkable impact on the quality and prolongation of human lives. An effective strategy to fight AMR is the method PhotoDynamic Therapy (PDT). PDT is based on a joint action of a photosensitizer, oxygen, and light within a specific spectrum. This results in the generation of singlet oxygen and other reactive oxygen species that can inactivate the pathogenic cells without further regrowth. This study presents the efficacy of a new Pd(II)- versus Zn(II)-phthalocyanine complexes with peripheral positions of methylpyridiloxy substitution groups (pPdPc and ZnPcMe) towards Gram-negative bacteria Aeromonas hydrophila (A.hydrophila). Zn(II)-phthalocyanine, ZnPcMe was used as a reference compound for in vitro studies, bacause it is well-known with a high photodynamic inactivation ability for different pathogenic microorganisms. The studied new isolates of A.hydrophila were antibiotic-resistant (R) and sensitive (S) strains. The photoinactivation results showed a full effect with 8 µM pPdPc for S strain and with 5 µM ZnPcMe for both R and S strains. Comparison between both new isolates of A.hydrophila (S and R) suggests that the uptakes and more likely photoinactivation efficacy of the applied phthalocyanines are independent of the drug sensitivity of the studied strains.

Preliminary Studies of Antimicrobial Activity of New Synthesized Hybrids of 2-Thiohydantoin and 2-Quinolone Derivatives Activated with Blue Light

Thiohydantoin and quinolone derivatives have attracted researchers' attention because of a broad spectrum of their medical applications. The aim of our research was to synthesize and analyze the antimicrobial properties of novel 2-thiohydantoin and 2-quinolone derivatives. For this purpose, two series of hybrid compounds were synthesized. Both series consisted of 2-thiohydantoin core and 2-quinolone derivative ring, however one of them was enriched with an acetic acid group at N3 atom in 2-thiohydantoin core. Antibacterial properties of these compounds were examined against bacteria: Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. The antimicrobial assay was carried out using a serial dilution method to obtain the MIC. The influence of blue light irradiation on the tested compounds was investigated. The relative yield of singlet oxygen (1O2*, 1Δg) generation upon excitation with 420 nm was determined by a comparative method, employing perinaphthenone (PN) as a standard. Antimicrobial properties were also investigated after blue light irradiation of the suspensions of the hybrids and bacteria placed in microtitrate plates. Preliminary results confirmed that some of the hybrid compounds showed bacteriostatic activity to the reference Gram-positive bacterial strains and a few of them were bacteriostatic towards Gram-negative bacteria, as well. Blue light activation enhanced bacteriostatic effect of the tested compounds.

In situ Forming Hyperbranched PEG-Thiolated Hyaluronic Acid Hydrogels With Honey-Mimetic Antibacterial Properties

The rapidly increasing resistance of bacteria to currently approved antibiotic drugs makes surgical interventions and the treatment of bacterial infections increasingly difficult. In recent years, complementary strategies to classical antibiotic therapy have, therefore, gained importance. One of these strategies is the use of medicinal honey in the treatment of bacterially colonized wounds. One of the several bactericidal effects of honey is based on the in situ generation of hydrogen peroxide through the activity of the enzyme glucose oxidase. The strategy underlying this work is to mimic this antibacterial redox effect of honey in an injectable, biocompatible, and rapidly forming hydrogel. The hydrogel was obtained by thiol–ene click reaction between hyperbranched polyethylene glycol diacrylate (HB PEGDA), synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization, and thiolated hyaluronic acid (HA-SH). After mixing 500 µL HB PEGDA (10%, w/w) and 500 µL HA-SH (1%, w/w) solutions, hydrogels formed in ∼60 s (HB PEGDA/HA-SH 10.0–1.0), as assessed by the tube inverting test. The HB PEGDA/HA-SH 10.0–1.0 hydrogel (200 µL) was resistant to in vitro dissolution in water for at least 64 days, absorbing up to 130 wt% of water. Varying glucose oxidase (GO) amounts (0–500 U/L) and constant glucose content (2.5 wt%) were loaded into HB PEGDA and HA-SH solutions, respectively, before hydrogel formation. Then, the release of H₂O₂ was evaluated through a colorimetric pertitanic acid assay. The GO content of 250 U/L was selected, allowing the formation of 10.8 ± 1.4 mmol H₂O₂/L hydrogel in 24 h, under static conditions. The cytocompatibility of HB PEGDA/HA-SH 10.0–1.0 hydrogels loaded with different GO activities (≤ 500 U/L) at a constant glucose amount (2.5 wt%) was investigated by in vitro assays at 24 h with L929 and HaCaT cell lines, according to DIN EN ISO 10993-5. The tests showed cytocompatibility for GO enzyme activity up to 250 U/L for both cell lines. The antibacterial activity of HB PEGDA/HA-SH 10.0–1.0 hydrogels loaded with increasing amounts of GO was demonstrated against various gram-positive bacteria (S. aureus and S. epidermidis), antibiotic-resistant gram-positive bacteria (MRSA and MRSE), gram-negative bacteria (P. aeruginosa, E. coli, and A. baumanii), and antibiotic-resistant gram-negative strains (P. aeruginosa and E. coli) using agar diffusion tests. For all gram-positive bacterial strains, increasing efficacy was measured with increasing GO activity. For the two P. aeruginosa strains, efficacy was shown only from an enzyme activity of 125 U/L and for E. coli and A. baumanii, efficacy was shown only from 250 U/L enzyme activity. HB PEGDA/HA-SH 10.0–1.0 hydrogels loaded with ≤250 U/L GO and 2.5 wt% glucose are promising formulations due to their fast-forming properties, cytocompatibility, and ability to produce antibacterial H₂O₂, warranting future investigations for bacterial infection treatment, such as wound care.

Highly Potent Photoinactivation of Bacteria Using a Water-Soluble, Cell-Permeable, DNA-Binding Photosensitizer

Antimicrobial photodynamic therapy (APDT) employs a photosensitizer, light, and molecular oxygen to treat infectious diseases via oxidative damage, with a low likelihood for the development of resistance. For optimal APDT efficacy, photosensitizers with cationic charges that can permeate bacteria cells and bind intracellular targets are desired to not limit oxidative damage to the outer bacterial structure. Here we report the application of brominated DAPI (Br-DAPI), a water-soluble, DNA-binding photosensitizer for the eradication of both Gram-negative and Gram-positive bacteria (as demonstrated on N99 Escherichia coli and Bacillus subtilis, respectively). We observe intracellular uptake of Br-DAPI, ROS-mediated bacterial cell death via one- and two-photon excitation, and selective photocytotoxicity of bacteria over mammalian cells. Photocytotoxicity of both N99 E. coli and B. subtilis occurred at submicromolar concentrations (IC₅₀ = 0.2-0.4 μM) and low light doses (5 min irradiation times, 4.5 J cm^-2 dose), making it superior to commonly employed APDT phenothiazinium photosensitizers such as methylene blue. Given its high potency and two-photon excitability, Br-DAPI is a promising novel photosensitizer for in vivo APDT applications.

Can Gram-Negative Bacteria Develop Resistance to Antimicrobial Blue Light Treatment?

Antimicrobial blue light (aBL) treatment is considered low risk for the development of bacterial resistance and tolerance due to its multitarget mode of action. The aim of the current study was to demonstrate whether tolerance development occurs in Gram-negative bacteria. We evaluated the potential of tolerance/resistance development in Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa and demonstrated that representative Gram-negative bacteria may develop tolerance to aBL. The observed adaption was a stable feature. Assays involving E. coli K-12 tolC-, tolA-, umuD-, and recA-deficient mutants revealed some possible mechanisms for aBL tolerance development.

Stimuli-Responsive Nanoplatform-Assisted Photodynamic Therapy Against Bacterial Infections

Bacterial infections are common diseases causing tremendous deaths in clinical settings. It has been a big challenge to human beings because of the antibiotics abuse and the newly emerging microbes. Photodynamic therapy (PDT) is a reactive oxygen species-based therapeutic technique through light-activated photosensitizer (PS). Recent studies have highlighted the potential of PDT as an alternative method of antibacterial treatment for its broad applicability and high efficiency. However, there are some shortcomings due to the low selectivity and specificity of PS. Growing evidence has shown that drug delivery nanoplatforms have unique advantages in enhancing therapeutic efficacy of drugs. Particularly, stimuli-responsive nanoplatforms, as a promising delivery system, provide great opportunities for the effective delivery of PS. In the present mini-review, we briefly introduced the unique microenvironment in bacterial infection tissues and the application of PDT on bacterial infections. Then we review the stimuli-responsive nanoplatforms (including pH-, enzymes-, redox-, magnetic-, and electric-) used in PDT against bacterial infections. Lastly, some perspectives have also been proposed to further promote the future developments of antibacterial PDT.

Optimization of Streptococcus agalactiae Biofilm Culture in a Continuous Flow System for Photoinactivation Studies

Streptococcus agalactiae is a relevant cause of neonatal mortality. It can be transferred to infants via the vaginal tract and cause meningitis, pneumonia, arthritis, or sepsis, among other diseases. The cause of therapy ineffectiveness and infection recurrence is the growth of bacteria as biofilms. To date, several research teams have attempted to find a suitable medium for the cultivation of S. agalactiae biofilms. Among others, simulated vaginal fluid has been used; however, biofilm production in this medium has been found to be lower than that in tryptic soy broth. We have previously shown that S. agalactiae can be successfully eradicated by photoinactivation in planktonic culture, but there have been no studies on biofilms. The aim of this study was to optimize S. agalactiae biofilm culture conditions to be used in photoinactivation studies. We compared biofilm production by four strains representing the most common serotypes in four different broth media with crystal violet staining. Then, we evaluated stationary biofilm culture in microtiter plates and biofilm growth in a CDC Biofilm Reactor® (BioSurface Technologies, Bozeman, MT, USA) under continuous flow conditions. Subsequently, we applied Rose Bengal-mediated photoinactivation to both biofilm models. We have shown that photoinactivation is efficient in biofilm eradication and is not cyto/phototoxic to human keratinocytes. We found conditions allowing for stable and repetitive S. agalactiae biofilm growth in continuous flow conditions, which can be successfully utilized in photoinactivation assays and potentially in all other antibacterial studies.

Photodynamic Therapy Review: Principles, Photosensitizers, Applications, and Future Directions

Photodynamic therapy (PDT) is a minimally invasive therapeutic modality that has gained great attention in the past years as a new therapy for cancer treatment. PDT uses photosensitizers that, after being excited by light at a specific wavelength, react with the molecular oxygen to create reactive oxygen species in the target tissue, resulting in cell death. Compared to conventional therapeutic modalities, PDT presents greater selectivity against tumor cells, due to the use of photosensitizers that are preferably localized in tumor lesions, and the precise light irradiation of these lesions. This paper presents a review of the principles, mechanisms, photosensitizers, and current applications of PDT. Moreover, the future path on the research of new photosensitizers with enhanced tumor selectivity, featuring the improvement of PDT effectiveness, has also been addressed. Finally, new applications of PDT have been covered.

Photodynamic Therapy for the Treatment and Diagnosis of Cancer-A Review of the Current Clinical Status

Photodynamic therapy (PDT) has been used as an anti-tumor treatment method for a long time and photosensitizers (PS) can be used in various types of tumors. Originally, light is an effective tool that has been used in the treatment of diseases for ages. The effects of combination of specific dyes with light illumination was demonstrated at the beginning of 20th century and novel PDT approaches have been developed ever since. Main strategies of current studies are to reduce off-target effects and improve pharmacokinetic properties. Given the high interest and vast literature about the topic, approval of PDT as the first drug/device combination by the FDA should come as no surprise. PDT consists of two stages of treatment, combining light energy with a PS in order to destruct tumor cells after activation by light. In general, PDT has fewer side effects and toxicity than chemotherapy and/or radiotherapy. In addition to the purpose of treatment, several types of PSs can be used for diagnostic purposes for tumors. Such approaches are called photodynamic diagnosis (PDD). In this Review, we provide a general overview of the clinical applications of PDT in cancer, including the diagnostic and therapeutic approaches. Assessment of PDT therapeutic efficacy in the clinic will be discussed, since identifying predictors to determine the response to treatment is crucial. In addition, examples of PDT in various types of tumors will be discussed. Furthermore, combination of PDT with other therapy modalities such as chemotherapy, radiotherapy, surgery and immunotherapy will be emphasized, since such approaches seem to be promising in terms of enhancing effectiveness against tumor. The combination of PDT with other treatments may yield better results than by single treatments. Moreover, the utilization of lower doses in a combination therapy setting may cause less side effects and better results than single therapy. A better understanding of the effectiveness of PDT in a combination setting in the clinic as well as the optimization of such complex multimodal treatments may expand the clinical applications of PDT.