Antimicrobial photodynamic therapy for methicillin-resistant Staphylococcus aureus infection

Zinc Complexes of Cationic Ammonium Phenyl and Methylpyridinium Porphyrins Display Synergistic Anti-HIV‑1 and Broad-Spectrum Antibacterial Activity

This study presents a pioneering series of cationic porphyrins with promising synergistic antimicrobial and anti-HIV properties, particularly effective against drug-resistant strains. The synthesized porphyrins, including P 3 AmM, PAm 3 M, and c-P 2 Am 2 M, as well as their zinc-(II) complexes (P 3 AmZM, PAm 3 ZM, and c-P 2 Am 2 ZM), were developed through strategic methylation of primary amino groups in precursor porphyrins, addressing steric challenges associated with repetitive amine alkylation. Under photodynamic therapy (PDT) conditions, these compounds exhibited notable suppression of HIV-1 entry and infection, in addition to demonstrating potent antibacterial activity against drug-resistant Escherichia coli and Staphylococcus aureus. Bacterial growth kinetics indicated reduced proliferation and biofilm formation over a five-day period, underscoring their efficacy as antibacterial agents. Compounds P 3 AmZM, PAm 3 ZM, c-P 2 Am 2 M, c-P 2 Am 2 ZM, and PAm 3 M displayed enhanced antibacterial potency, with S. aureus showing greater susceptibility. Disc diffusion assays further confirmed the superior efficacy of c-P 2 Am 2 M and c-P 2 Am 2 ZM, particularly against S. aureus. Computational molecular docking simulations highlighted the robust binding affinity and interaction profiles of c-P 2 Am 2 M and c-P2Am 2 ZM with key HIV targets. These findings position these novel cationic porphyrins as potential dual-action therapeutics, combining synergistic anti-HIV efficacy with potent antibacterial activity under PDT conditions.

An In vitro Study on the Antibacterial Effect of a Combined Photodynamic and Sonodynamic Therapy Using IR780 Iodide-loaded Mesoporous Silica Nanoparticles Against P. aeruginosa and Multi-Drug Resistant P. aeruginosa

BACKGROUND

The aim of this study was to investigate the antimicrobial photodynamic, sonodynamic, and combined photodynamic and sonodynamic potentials of IR780 iodide loaded mesoporous silica nanoparticles against gram-negative Pseudomonas aeruginosa (P. aeruginosa) and multi drug resistant Pseudomonas aeruginosa (MDR P. aeruginosa).

METHODS

IR780 iodide loaded mesoporous silica nanoparticles were synthesized, and their antimicrobial photodynamic and sonodynamic potentials against one P. aeruginosa strain, and one MDR P. aeruginosa strain were investigated. Laser irradiation was achieved via a 785 nm diode laser (500 mW/cm2, 5 min). Ultrasound irradiation was achieved via a 1-MHz ultrasound unit (1.5 W/cm2, 50% duty cycle, 3 min). Viable bacterial cells were counted by serial dilution method. Data were analyzed by ANOVA followed by Tukey's test (p ≤ 0.05).

RESULTS

The results revealed that for P. aeruginosa, the combined photodynamic therapy (PDT) and sonodynamic therapy (SDT) showed a 44% reduction in bacterial cell viability as compared to 18% and 31% when exposed to SDT alone and PDT alone, respectively. For MDR. P. aeruginosa, the combined treatment resulted in a 45% reduction in bacterial cell viability, as compared to 14% and 30% when exposed to SDT alone and PDT alone, respectively. The killing effect was mainly due to the photodynamic and sonodynamic effects of the nanoparticles, mainly caused by singlet oxygen. No photothermal effect was involved in the killing.

CONCLUSION

The results of this study demonstrated that IR780 iodide-loaded mesoporous silica nanoparticles have the potential to be utilized as photo/sono therapeutic agents for the inactivation of drug-resistant bacteria.

Carbon Dots in Photodynamic/Photothermal Antimicrobial Therapy

Antimicrobial resistance (AMR) presents an escalating global challenge as conventional antibiotic treatments become less effective. In response, photodynamic therapy (PDT) and photothermal therapy (PTT) have emerged as promising alternatives. While rooted in ancient practices, these methods have evolved with modern innovations, particularly through the integration of lasers, refining their efficacy. PDT harnesses photosensitizers to generate reactive oxygen species (ROS), which are detrimental to microbial cells, whereas PTT relies on heat to induce cellular damage. The key to their effectiveness lies in the utilization of photosensitizers, especially when integrated into nano- or micron-scale supports, which amplify ROS production and enhance antimicrobial activity. Over the last decade, carbon dots (CDs) have emerged as a highly promising nanomaterial, attracting increasing attention owing to their distinctive properties and versatile applications, including PDT and PTT. They can not only function as photosensitizers, but also synergistically combine with other photosensitizers to enhance overall efficacy. This review explores the recent advancements in CDs, underscoring their significance and potential in reshaping advanced antimicrobial therapeutics.

Exploration of the Graphene Quantum Dots-Blue Light Combination: A Promising Treatment against Bacterial Infection

Graphene Quantum Dots (GQDs) have shown the potential for antimicrobial photodynamic treatment, due to their particular physicochemical properties. Here, we investigated the activity of three differently functionalized GQDs-Blue Luminescent GQDs (L-GQDs), Aminated GQDs (NH2-GQDs), and Carboxylated GQDs (COOH-GQDs)-against E. coli. GQDs were administrated to bacterial suspensions that were treated with blue light. Antibacterial activity was evaluated by measuring colony forming units (CFUs) and metabolic activities, as well as reactive oxygen species stimulation (ROS). GQD cytotoxicity was then assessed on human colorectal adenocarcinoma cells (Caco-2), before setting in an in vitro infection model. Each GQD exhibits antibacterial activity inducing ROS and impairing bacterial metabolism without significantly affecting cell morphology. GQD activity was dependent on time of exposure to blue light. Finally, GQDs were able to reduce E. coli burden in infected Caco-2 cells, acting not only in the extracellular milieu but perturbating the eukaryotic cell membrane, enhancing antibiotic internalization. Our findings demonstrate that GQDs combined with blue light stimulation, due to photodynamic properties, have a promising antibacterial activity against E. coli. Nevertheless, we explored their action mechanism and toxicity on epithelial cells, fixing and standardizing these infection models.

Bacterial resistance to antimicrobial photodynamic therapy: A critical update

Bacterial antibiotic resistance is one of the most significant challenges for public health. The increase in bacterial resistance, mainly due to microorganisms harmful to health, and the need to search for alternative treatments to contain infections that cannot be treated by conventional antibiotic therapy has been aroused. An alternative widely studied in recent decades is antimicrobial photodynamic therapy (aPDT), a treatment that can eliminate microorganisms through oxidative stress. Although this therapy has shown satisfactory results in infection control, it is still controversial in the scientific community whether bacteria manage to develop resistance after successive applications of aPDT. Thus, this work provides an overview of the articles that performed successive aPDT applications in models using bacteria published since 2010, focusing on sublethal dose cycles, highlighting the main PSs tested, and addressing the possible mechanisms for developing tolerance or resistance to aPDT, such as efflux pumps, biofilm formation, OxyR and SoxRS systems, catalase and superoxide dismutase enzymes and quorum sensing.

Studying the viability and growth kinetics of vancomycin-resistant Enterococcus faecalis V583 following femtosecond laser irradiation (420-465 nm)

Enterococcus faecalis is among the most resistant bacteria found in infected root canals. The demand for cutting-edge disinfection methods has rekindled research on photoinactivation with visible light. This study investigated the bactericidal activity of femtosecond laser irradiation against vancomycin-resistant Enterococcus faecalis V583 (VRE). The effect of parameters such as wavelength and energy density on the viability and growth kinetics of VRE was studied to design an optimized laser-based antimicrobial photoinactivation approach without any prior addition of exogenous photosensitizers. The most effective wavelengths were 430 nm and 435 nm at a fluence of 1000 J/cm2, causing a nearly 2-log reduction (98.6% and 98.3% inhibition, respectively) in viable bacterial counts. The colony-forming units and growth rate of the laser-treated cultures were progressively decreased as energy density or light dose increased at 445 nm but reached a limit at 1250 J/cm2. At a higher fluence of 2000 J/cm2, the efficacy was reduced due to a photobleaching phenomenon. Our results highlight the importance of optimizing laser exposure parameters, such as wavelength and fluence, in bacterial photoinactivation experiments. To our knowledge, this is the first study to report an optimized wavelength for the inactivation of VRE using visible femtosecond laser light.

Concanavalin A Delivers a Photoactive Protein to the Bacterial Wall

Modular supramolecular complexes, where different proteins are assembled to gather targeting capability and photofunctional properties within the same structures, are of special interest for bacterial photodynamic inactivation, given their inherent biocompatibility and flexibility. We have recently proposed one such structure, exploiting the tetrameric bacterial protein streptavidin as the main building block, to target S. aureus protein A. To expand the palette of targets, we have linked biotinylated Concanavalin A, a sugar-binding protein, to a methylene blue-labelled streptavidin. By applying a combination of spectroscopy and microscopy, we demonstrate the binding of Concanavalin A to the walls of Gram-positive S. aureus and Gram-negative E. coli. Photoinactivation is observed for both bacterial strains in the low micromolar range, although the moderate affinity for the molecular targets and the low singlet oxygen yields limit the overall efficiency. Finally, we apply a maximum entropy method to the analysis of autocorrelation traces, which proves particularly useful when interpreting signals measured for diffusing systems heterogeneous in size, such as fluorescent species bound to bacteria.

Easy and versatile cellulosic support inhibiting broad spectrum strains: synergy between photodynamic antimicrobial therapy and polymyxin B

Despite advances achieved in the health field over the last decade, infections caused by resistant bacterial strains are an increasingly important societal issue that needs to be addressed. New approaches have already been developed to overcome this problem. Photodynamic antimicrobial chemotherapy (PACT) could provide a promising alternative method to eradicate microbes. This approach has already inspired the development of innovative surfaces. Interesting results were achieved against Gram-positive bacteria, but it also appeared that Gram-negative strains, especially Pseudomonas aeruginosa, were less sensitive to PACT. However, materials coated with cationic porphyrins have already proven their wide-spectrum activity, but these materials were not suitable for industrial-scale production. The main aim of this work was the design of a large-scale evolutionary material based on PACT and antibiotic prophylaxis. Transparent regenerated cellulose has been simply impregnated with a usual cationic porphyrin (N-methylpyridyl) and an antimicrobial peptide (polymyxin B). In addition to its photophysical properties, this film exhibited a wide-spectrum bactericidal activity over 4 days despite daily application of fresh bacterial inoculums. The efficiency of PACT and polymyxin B combination could help to reduce the emergence of bacterial multi-resistant strains and we believe that this kind of material would provide an excellent opportunity to prevent bacterial contamination of bandages or packaging.

Toluidine blue O photosensitizer combined with caffeic acid improves antibacterial performance by increasing the permeability of cell membrane

Photodynamic therapy has always been an antibacterial tool for solving multi-drug resistant bacteria problem, but the side effects and the low efficiency due to the high aggregation and low solubility of photosensitizers limit its application. Due to the anti-inflammatory effect of caffeic acid, two novel photosensitizers (CA-1-TBO, CA-TBO) were synthesized by conjugating caffeic acid with toluidine blue O (TBO). The structures have been characterized by 1HNMR and high-resolution mass spectrometry. The UV-vis absorption, fluorescence spectra and the octanol-water partition coefficient of two photosensitizers were measured to evaluate their photophysical properties and hydrophilic/hydrophobic properties. Compared with parent TBO, the two modified photosensitizers have shown a higher quantum yield and kinetics constants of singlet oxygen, which has been supported by the simulation results of density functional theory. As drug-resistant representatives of gram-positive and gram-negative bacteria, respectively, S. aureus and P. aeruginosa have been used for in vitro antibacterial experiments. The sterilization efficiencies of the two modified photosensitizers far exceed that of parent TBO. The results of the octanol-water partition coefficient and fluorescence quantification showed that modified photosensitizers CA-1-TBO and CA-TBO could be more accumulated than parent TBO. Based on scanning electron microscopy images, protein gel electrophoresis, and the conductivity of the bacterial solution, the possible mechanism of improved antibacterial photodynamic efficiencies could be induced by membrane permeability due to the caffeic acid effect. The findings demonstrate the significant potential of natural phenolic compounds in the development of photosensitizer molecules with characteristics such as more efficient, biocompatible and less side effects.

Investigating Photoactive Antimicrobials as Alternatives (or Adjuncts) to Traditional Therapy

Photodynamic therapy (PDT) is an established therapy used for the treatment of cutaneous skin cancers and other non-infective ailments. There has been recent interest in the opportunity to use aPDT (antimicrobial PDT) to treat skin and soft tissue infections. PDT utilizes photosensitizers that infiltrate all cells and "sensitize" them to a given wavelength of light. The photosensitizer is simply highly absorbent to a given wavelength of light and when excited will produce, in the presence of oxygen, damaging oxygen radicals and singlet oxygen. Bacterial cells are comparatively poor at combatting oxidative stress when compared with human cells therefore a degree of selective toxicity can be achieved with aPDT.In this chapter, we outline methodologies for testing aPDT in vitro using standard lab equipment.

Exploring alternative strategies for Staphylococcus aureus nasal decolonization: insights from preclinical studies

Nasal decolonization of Staphylococcus aureus with the antibiotic mupirocin is a common clinical practice before complex surgical procedures, to prevent hospital acquired infections. However, widespread use of mupirocin has led to the development of resistant S. aureus strains and there is a limited scope for developing new antibiotics for S. aureus nasal decolonization. It is therefore necessary to develop alternative and nonantibiotic nasal decolonization methods. In this review, we broadly discussed the effectiveness of different nonantibiotic antimicrobial agents that are currently not in clinical practice, but are experimentally proved to be efficacious in promoting S. aureus nasal decolonization. These include lytic bacteriophages, bacteriolytic enzymes, tea tree oil, apple vinegar, and antimicrobial peptides. We have also discussed the possibility of using photodynamic therapy for S. aureus nasal decolonization. This article highlights the importance of further large scale clinical studies for selecting the most suitable and alternative nasal decolonizing agent.

Cyclodextrin: A prospective nanocarrier for the delivery of antibacterial agents against bacteria that are resistant to antibiotics

Supramolecular chemistry introduces us to the macrocyclic host cyclodextrin, which has a hydrophobic cavity. The hydrophobic cavity has a higher affinity for hydrophobic guest molecules and forms host-guest complexation with non-covalent interaction. Three significant cyclodextrin kinds are α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. The most often utilized is β-cyclodextrin (β-CD). An effective weapon against bacteria that are resistant to antibiotics is cyclodextrin. Several different kinds of cyclodextrin nanocarriers (β-CD, HP-β-CD, Meth-β-CD, cationic CD, sugar-grafted CD) are utilized to enhance the solubility, stability, dissolution, absorption, bioavailability, and permeability of the antibiotics. Cyclodextrin also improves the effectiveness of antibiotics, antimicrobial peptides, metallic nanoparticles, and photodynamic therapy (PDT). Again, cyclodextrin nanocarriers offer slow-release properties for sustained-release formulations where steady-state plasma antibiotic concentration is needed for an extended time. A novel strategy to combat bacterial resistance is a stimulus (pH, ROS)-responsive antibiotics released from cyclodextrin carrier. Once again, cyclodextrin traps autoinducer (AI), a crucial part of bacterial quorum sensing, and reduces virulence factors, including biofilm formation. Cyclodextrin helps to minimize MIC in particular bacterial strains, keep antibiotic concentrations above MIC in the infection site and minimize the possibility of antibiotic and biofilm resistance. Sessile bacteria trapped in biofilms are more resistant to antibiotic therapy than bacteria in a planktonic form. Cyclodextrin also involves delivering antibiotics to biofilm and resistant bacteria to combat bacterial resistance.

Improving the Management and Treatment of Diabetic Foot Infection: Challenges and Research Opportunities

Diabetic foot infection (DFI) management requires complex multidisciplinary care pathways with off-loading, debridement and targeted antibiotic treatment central to positive clinical outcomes. Local administration of topical treatments and advanced wound dressings are often used for more superficial infections, and in combination with systemic antibiotics for more advanced infections. In practice, the choice of such topical approaches, whether alone or as adjuncts, is rarely evidence-based, and there does not appear to be a single market leader. There are several reasons for this, including a lack of clear evidence-based guidelines on their efficacy and a paucity of robust clinical trials. Nonetheless, with a growing number of people living with diabetes, preventing the progression of chronic foot infections to amputation is critical. Topical agents may increasingly play a role, especially as they have potential to limit the use of systemic antibiotics in an environment of increasing antibiotic resistance. While a number of advanced dressings are currently marketed for DFI, here we review the literature describing promising future-focused approaches for topical treatment of DFI that may overcome some of the current hurdles. Specifically, we focus on antibiotic-impregnated biomaterials, novel antimicrobial peptides and photodynamic therapy.

Coping with the ESKAPE pathogens: Evolving strategies, challenges and future prospects

Globally, the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are the major cause of nosocomial infections. These pathogens are multidrug resistant, and their negative impacts have brought serious health challenges and economic burden on many countries worldwide. Thus, this narrative review exploits different emerging alternative therapeutic strategies including combination antibiotics, antimicrobial peptides ((AMPs), bacteriophage and photodynamic therapies used in the treatment of the ESKAPE pathogens, their merits, limitations, and future prospects. Our findings indicate that ESKAPE pathogens exhibit resistance to drug using different mechanisms including drug inactivation by irreversible enzyme cleavage, drug-binding site alteration, diminution in permeability of drug or drug efflux increment to reduce accumulation of drug as well as biofilms production. However, the scientific community has shown significant interest in using these novel strategies with numerous benefits although they have some limitations including but not limited to instability and toxicity of the therapeutic agents, or the host developing immune response against the therapeutic agents. Thus, comprehension of resistance mechanisms of these pathogens is necessary to further develop or modify these approaches in order to overcome these health challenges including the barriers of bacterial resistance.

Photodynamic therapy for treating infected skin wounds: A systematic review and meta-analysis from randomized clinical trials

BACKGROUND

Infected skin wounds represent a public health problem that effects 20 million people worldwide. Photodynamic therapy (PDT) is a treatment option with excellent results against several infections.

OBJECTIVE

This study aimed to perform a systematic review and meta-analysis on PDT efficacy for treating infected wounds based on randomized clinical trials (RCTs).

METHODS

PubMed, Scopus, Web of Science, SciELO, and the Cochrane library were searched. The Delphi List criteria and the Revised Cochrane risk-of-bias (Rob 2) were used for evaluating the quality of clinical trials. Meta-analyses were performed with the random-effect model. The odds ratio was the effect measure for binary outcomes, while the standard mean difference was used for continuous outcomes. The trim-and-fill method was used to detect small-study effects. The quality of evidence was verified for each outcome.

RESULTS

Only four out of 573 articles were selected for the qualitative and quantitative analyses. The most frequent cause of infected wounds was impaired venous circulation (75%). All studies used red LED light. PDT reduced healing time and improved the healing process and wound oxygenation. Patients treated with PDT showed 15% to 17% (p = 0.0003/ I²=0%) lower microbial cell viability in the wound and a significantly smaller wound size (0.72 cm²/p = 0.0187/I²=0%) than patients treated with placebo or red-light exposure. There was a high level of evidence for each meta-analysis outcome.

CONCLUSION

PDT can be an excellent alternative treatment for infected skin wounds, though larger trials are needed.

Translational feasibility and efficacy of nasal photodynamic disinfection of SARS-CoV-2

The lack of therapeutic options to fight Covid-19 has contributed to the current global pandemic. Despite the emergence of effective vaccines, development of broad-spectrum antiviral treatment remains a significant challenge, in which antimicrobial photodynamic therapy (aPDT) may play a role, especially at early stages of infection. aPDT of the nares with methylene blue (MB) and non-thermal light has been successfully utilized to inactivate both bacterial and viral pathogens in the perioperative setting. Here, we investigated the effect of MB-aPDT to inactivate human betacoronavirus OC43 and SARS-CoV-2 in vitro and in a proof-of-principle COVID-19 clinical trial to test, in a variety of settings, the practicality, technical feasibility, and short-term efficacy of the method. aPDT yielded inactivation of up to 6-Logs in vitro, as measured by RT-qPCR and infectivity assay. From a photo-physics perspective, the in vitro results suggest that the response is not dependent on the virus itself, motivating potential use of aPDT for local destruction of SARS-CoV-2 and its variants. In the clinical trial we observed variable effects on viral RNA in nasal-swab samples as assessed by RT-qPCR attributed to aPDT-induced RNA fragmentation causing falsely-elevated counts. However, the viral infectivity in clinical nares swabs was reduced in 90% of samples and undetectable in 70% of samples. This is the first demonstration based on quantitative clinical viral infectivity measurements that MB-aPDT is a safe, easily delivered and effective front-line technique that can reduce local SARS-CoV-2 viral load.

Photodynamic therapy and combinatory treatments for the control of biofilm-associated infections

The advent of antimicrobial resistance has added considerable impact to infectious diseases both in the number of infections and healthcare costs. Furthermore, the relentless emergence of multidrug-resistant bacteria, particularly in the biofilm state, has made mandatory the discovery of new alternative antimicrobial therapies that are capable to eradicate resistant bacteria and impair the development of new forms of resistance. Amongst the therapeutic strategies for treating biofilms, antimicrobial photodynamic therapy (aPDT) has shown great potential in inactivating several clinically relevant micro-organisms, including antibiotic-resistant 'priority bacteria' declared by the WHO as critical pathogens. Its antimicrobial effect is centred on the basis that harmless low-intensity light stimulates a non-toxic dye named photosensitizer, triggering the production of reactive oxygen species upon photostimulation. In addition, combination therapies of aPDT with other antimicrobial agents (e.g. antibiotics) have also drawn considerable attention, as it is a multi-target strategy. Therefore, the present review highlights the recent advances of aPDT against biofilms, also covering progress on combination therapy.

Electrospun SF/PLGA/ICG Composite Nanofibrous Membranes for Potential Wound Healing and Tumor Therapy

Indocyanine green (ICG) is a near-infrared (NIR) organic reagent for clinical bioimaging and phototherapy. It is a suitable photosensitizer for photodynamic antimicrobial chemotherapy (PACT). In this study, various ICG-loaded nanofibrous membranes were prepared. The water vapor transmission rate (WVTR) of SF/PLGA/20ICG was 3040.49 ± 157.11 g·m−2 day−1, which allowed the maintenance of a humid environment above the wound. The growth inhibition rates for S. aureus and E. coli were 91.53% and 87.95%, respectively. The nanofibrous membranes exhibited excellent antimicrobial performance. Cellular experiments showed that the nanofibrous membranes have good cytocompatibility and antitumor efficacy. SF/PLGA/20ICG showed good potential for application in wound healing and cancer therapy.

pH-responsive curcumin-based nanoscale ZIF-8 combining chemophotodynamic therapy for excellent antibacterial activity

Antimicrobial photodynamic therapy (aPDT) is a highly attractive therapy due to its advantages of being a non-antibiotic procedure for reducing drug-resistant microbes. Curcumin (CCM) has been considered as a natural photosensitizer for PDT with prominent antibacterial, antifungal, and anti-proliferative activity. However, its excellent biological and pharmacological activities are limited because of its low solubility, rapid metabolization and instability. Herein, we reported a promising agent based on CCM-incorporated into zeolitic imidazolate framework-8 (ZIF@CCM). The as-prepared nanoparticle exhibited high drug loading capability (11.57%) and drug loading encapsulation (82.76%). Additionally, ZIF@CCM displayed a pH-responsive drug release behavior and chemophotodynamic therapy for excellent antibacterial activity. The underlying mechanism elucidated that Zn2+ released from ZIF-8 increased the permeability of the bacterial cell membrane with leakages of K+. The overproduction of extracellular ROS further resulted in the disrupted bacterial cell membrane and distorted bacterial morphology. Thus, ZIF@CCM-mediated photodynamic activation might be a promising treatment strategy for microbial inactivation.

Versatile Supramolecular Complex for Targeted Antimicrobial Photodynamic Inactivation

We report the development of a supramolecular structure endowed with photosensitizing properties and targeting capability for antimicrobial photodynamic inactivation. Our synthetic strategy uses the tetrameric bacterial protein streptavidin, labeled with the photosensitizer eosin, as the main building block. Biotinylated immunoglobulin G (IgG) from human serum, known to associate with Staphylococcus aureus protein A, was bound to the complex streptavidin-eosin. Fluorescence correlation spectroscopy and fluorescence microscopy demonstrate binding of the complex to S. aureus. Efficient photoinactivation is observed for S. aureus suspensions treated with IgG-streptavidin-eosin at concentrations higher than 0.5 μM and exposed to green light. The proposed strategy offers a flexible platform for targeting a variety of molecules and microbial species.

Empowering antimicrobial photodynamic therapy of Staphylococcus aureus infections with potassium iodide

Infections caused by the Gram-positive bacterium Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), impose a great burden on global healthcare systems. Thus, there is an urgent need for alternative approaches to fight staphylococcal infections, such as targeted antimicrobial photodynamic therapy (aPDT). We recently reported that targeted aPDT with the S. aureus-specific immunoconjugate 1D9-700DX can be effectively applied to eradicate MRSA. Nonetheless, the efficacy of aPDT in the human body may be diminished by powerful antioxidant activities. In particular, we observed that the efficacy of aPDT with 1D9-700DX towards MRSA was reduced in human plasma. Here we show that this antagonistic effect can be attributed to human serum albumin, which represents the largest pool of free thiols in plasma for trapping reactive oxygen species. Importantly, we also show that our targeted aPDT approach with 1D9-700DX can be empowered by the non-toxic inorganic salt potassium iodide (KI), which reacts with the singlet oxygen produced upon aPDT, resulting in the formation of free iodine. The targeted iodine formation allows full eradication of MRSA (more than 6-log reduction) without negatively affecting other non-targeted bacterial species or human cells. Altogether, we show that the addition of KI allows a drastic reduction of both the amount of the immunoconjugate 1D9-700DX and the irradiation time needed for effective elimination of MRSA by aPDT in the presence of human serum albumin.

Comparison of Antibacterial Activity and Wound Healing in a Superficial Abrasion Mouse Model of Staphylococcus aureus Skin Infection Using Photodynamic Therapy Based on Methylene Blue or Mupirocin or Both

Background: Antibiotic resistance and impaired wound healing are major concerns in S. aureus superficial skin infections, and new therapies are needed. Antimicrobial photodynamic therapy (aPDT) is a new therapeutic approach for infections, but it also improves healing in many wound models. Objective: To compare the antimicrobial activity and the effects on wound healing of aPDT based on Methylene Blue (MB-aPDT) with mupirocin treatment, either alone or in combination, in superficial skin wounds of S. aureus-infected mice. Additionally, to evaluate the clinical, microbiological, and cosmetic effects on wound healing. Materials and Methods: A superficial skin infection model of S. aureus was established in SKH-1 mice. Infected wounds were treated with MB-aPDT, MB-aPDT with a daily topical mupirocin or only with mupirocin. No treatment was carried out in control animals. Daily clinical and microbiological examinations were performed until complete clinical wound healing. Histopathological studies and statistical analysis were performed at the end of the study. Results: MB-aPDT treatment induced the best wound healing compared to mupirocin alone or to mupirocin plus MB-aPDT. Superficial contraction at 24 h and a greater reduction in size at 48 h, quicker detachment of the crust, less scaling, and absence of scars were observed. Histopathological studies correlated with clinical and gross findings. By contrast, mupirocin showed the highest logaritmic reduction of S. aureus. Conclusions: MB-aPDT and mupirocin treatments are effective in a murine superficial skin infection model of S. aureus. One session of MB-aPDT was the best option for clinical wound healing and cosmetic results. The addition of mupirocin to MB-aPDT treatment improved antimicrobial activity; however, it did not enhance wound healing. No synergistic antibacterial effects were detected.

Photophysical and Bactericidal Properties of Pyridinium and Imidazolium Porphyrins for Photodynamic Antimicrobial Chemotherapy

Despite advances achieved over the last decade, infections caused by multi-drug-resistant bacterial strains are increasingly becoming important societal issues that need to be addressed. New approaches have already been developed in order to overcome this problem. Photodynamic antimicrobial chemotherapy (PACT) could provide an alternative to fight infectious bacteria. Many studies have highlighted the value of cationic photosensitizers in order to improve this approach. This study reports the synthesis and the characterization of cationic porphyrins derived from methylimidazolium and phenylimidazolium porphyrins, along with a comparison of their photophysical properties with the well-known N-methylpyridyl (pyridinium) porphyrin family. PACT tests conducted with the tetracationic porphyrins of these three families showed that these new photosensitizers may offer a good alternative to the classical pyridinium porphyrins, especially against S.aureus and E.coli. In addition, they pave the way to new cationic photosensitizers by the means of derivatization through amide bond formation.

Photodynamic inactivation of Staphylococcus aureus using tetraethylene glycol-substituted Zn(II) phthalocyanine

Methicillin resistant Staphylococcus aureus infections are increasing, especially in intensive care units. A new method for photodynamic inactivation (PDI) generates reactive oxygen species by photosensitization to kill bacteria. We investigated the PDI effect of tetraethylene glycol-substituted Zn(II) phthalocyanine (TEG-P) on S. aureus strains including two standards (ATCC 25923 and ATCC 43400) and 20 clinically isolated methicillin sensitive and 20 methicillin resistance strains. We also investigated three treated groups: 650 nm laser only, TEG-P only and TEG-P + laser, plus one control group. Treatments included 0.5, 1, 2, 4, 8, 16, 32 µg/ml concentrations of TEG-P. No suppression of bacterial growth was observed in the control, laser only and TEG-P only groups whether or not S. aureus was methicillin resistant. Bacterial growth was suppressed by 85% using 8 µg/ml TEG-P and completely suppressed by 32 µg/ml TEG-P in the TEG-P + laser group. A combination of TEG-P + laser treatment may be an alternative to conventional antibiotics for routine treatment of S. aureus infections, although further investigation of the effect at the tissue level is required.

Improved antimicrobial properties of methylene blue attached to silver nanoparticles

Photosensitizing agents are the cornerstone of Photodynamic Therapy (PDT). They play an essential role in deactivation process of multidrug resistant pathogens and tumor treatments. In this work, we studied a photosensitizing agent made from mixture of Silver Nanoparticles (Ag NPs) and Methylene Blue (MB) which possess improved important characteristics like high photostability and high singlet oxygen yield. Ag NPs were synthesized by pulsed laser ablation technique in different aqueous solutions like polyvinylpyrrolidone (PVP), citrate and Deionized (DI) water. The synthesized AgNPs were characterized in depth using with transmission electron microscopy (TEM), UV-vis (UV-vis), and photoluminescence (PL) spectra. These Ag NPs were combined with MB and used to eradicate the Gram-negative bacteria, Escherichia coli (E. coli), and Gram-positive bacteria, Staphylococcus aureus (S. aureus). MB and Ag NPs mixture was found to possess higher antimicrobial activity and thus were more effective in killing both Gram -positive and Gram-negative bacteria in comparison to individual exposure of MB and Ag NPs. Additionally, the antimicrobial effects varied with respect to the size of nanoparticles as well as the medium used for their synthesis. The data from this study supports the potential use of the proposed method in PDT where standard photosensitizers have limitations.

Photodynamic Therapy as a New Treatment for Chronic Rhinosinusitis - A Systematic Review

This review examines the latest evidence for photodynamic therapy (PDT) in treating chronic rhinosinusitis. MedLine, EMBASE and TRIP Database searches were conducted using the terms: "photodynamic" or "phototherapy" or "photo" and "sinusitis" or "rhinosinusitis," date range January 2000 to May 2020. A total of 192 records were initially identified, after duplicates and exclusions, 9 full papers and 3 abstracts were included. All study types including in-vitro, animal and human studies were evaluated. Whilst there is in-vitro evidence for the efficacy of PDT's bactericidal effect on drug resistant bacteria and biofilm viability, there are few clinical studies. PDT is a promising area of research, but larger, focused studies looking at the safety, delivery, efficacy, and patient selection are required before it can be considered a viable treatment for CRS.

Evaluation of antimicrobial photodynamic therapy on wounds infected by Staphylococcus aureus in animal models

BACKGROUND

Antibiotic-resistant Staphylococcus aureus bacteria are one of the expanding challenges. The purpose of current study is to evaluate the antimicrobial effect of photodynamic therapy (aPDT) on wounds infected to Staphylococcus aureus.

METHODS

In this study, 40 six-month-old rats were divided into 4 groups: control, photosensitizer (PS), laser, and aPDT. A full-thickness wound was created on their skin and it was infected by Staphylococcus aureus. For aPDT, the Indocyanine Green (Germany, Nürnberg, A.R.C. Laser, EmunDo) photosensitive agent and laser diod 810 nm (Germany, Nürnberg, A.R.C. Laser) was utilized. The wound healing procedure was monitored every 24 h until the 12th day with photography. The number of the bacteria was counted on the 12th day also. All results were compared using ANOVA and Tukey post hoc tests. Significance level was considered P-Value < 0.05.

RESULTS

The average area of wound reduced in days 5-11th in photosensitizer, laser, and aPDT, respectively. The absolute colonization rate of bacteria in the wounds showed a significant decrease in two groups laser and aPDT compared to the control group. However, the lowest value was for the aPDT.

CONCLUSION

In the conditions of this study, it emerged that aPDT and laser have an antimicrobial effect against antibiotic-resistant bacteria (particularly Staphylococcus aureus) and improve wound healing.

Screening of antimicrobial synergism between phenolic acids derivatives and UV-A light radiation

The objective of this study was to investigate synergistic antibacterial activity based on a combination of UV-A light and three classes of food grade compounds: benzoic acid derivatives, cinnamic acid derivatives, and gallates. By using Escherichia coli O157:H7 as the model strain, it was observed that three cinnamic acid derivatives (ferulic acid, coumaric acid, and caffeic acid) and one benzoic acid derivative (2,5-dihydroxybenzoic acid) presented strong synergistic antibacterial activity with UV-A light radiation, where 1 mM levels of these compounds plus with 15 min of UV-A light (total light dose of 6.1 cm^-2) led to more than 7-log CFU mL^-1 of bacterial inactivation. In contrast, synergistic antibacterial activity between UV-A light and most benzoic acid derivatives (benzoic acid, gallic acid, vanillic acid, and 2,5-dimethoxybenzoic acid) were only observed after higher concentrations of these compounds were applied (10 mM). Lastly, from the three gallates tested (methyl gallate, ethyl gallate, and propyl gallate), only propyl gallate showed strong antibacterial synergism with UV-A light, where 10 mM of propyl gallate plus 15 min of UV-A light led to approximately 6.5-log of bacterial reduction. Presence of antioxidant compounds mitigated the light-mediated antibacterial activity of gallic acid, 2,5-dihydroxybenzoic acid, and propyl gallate. Similarly, the light-mediated antibacterial activity of these compounds was significantly (P < 0.05) reduced against metabolic-inhibited bacterial cells (sodium azide pretreatment). On the other hand, the antibacterial synergism between ferulic acid and UV-A light was not affected by the presence of antioxidants or the metabolic state of the bacterial cells. Due to the increasing concerns of antimicrobial resistant (AMR) pathogens, the study also investigated the proposed synergistic treatment on AMR Salmonella. Combinations of 1 mM of ferulic acid or 1 mM of 2,5-dihydroxybenzoic acid with UV-A light radiation was able to inactivate more than 6-log of a multi-drug resistant Salmonella Typhimurium strain.

Efflux pump inhibitors: new updates

The discovery of antibiotics ought to have ended the issue of bacterial infections, but this was not the case as it has led to the evolution of various mechanisms of bacterial resistance against various antibiotics. The efflux pump remains one of the mechanisms through which organisms develop resistance against antibiotics; this is because organisms can extrude most of the clinically relevant antibiotics from the interior cell environment to the exterior environment via the efflux pumps. Efflux pumps are thought to contribute significantly to biofilm formation as highlighted by various studies. Therefore, the inhibition of these efflux pumps can be a potential way of improving the activity of antibiotics, particularly now that the discovery of novel antibiotics is becoming tedious. Efflux pump inhibitors (EPIs) are molecules that can inhibit efflux pumps; they have been considered potential therapeutic agents for rejuvenating the activity of antibiotics that have already lost their activity against bacteria. However, studies are yet to determine the specific substrates for such pumps; the effect of altered efflux activity of these pumps on biofilm formation is still being investigated. A clear knowledge of the involvement of efflux pumps in biofilm development could aid in developing new agents that can interfere with their function and help to prevent biofilms formation; thereby, improving the outcome of treatment strategies. This review focuses on the novel update of EPIs and discusses the evidence of the roles of efflux pumps in biofilm formation; the potential approaches towards overcoming the increasing problem of biofilm-based infections are also discussed.

Antimicrobial Photothermal Treatment of Pseudomonas Aeruginosa by a Carbon Nanoparticles-Polypyrrole Nanocomposite

BACKGROUND

Nowadays, it is needed to explore new routes to treat infectious bacterial pathogens due to prevalence of antibiotic-resistant bacteria. Antimicrobial photothermal therapy (PTT), as a new strategy, eradicates pathogenic bacteria.

OBJECTIVE

In this study, the antimicrobial effects of a carbon nanoparticles-polypyrrole nanocomposite (C-PPy) upon laser irradiation were investigated to destroy the pathogenic gram-negative Pseudomonas aeruginosa.

MATERIAL AND METHODS

In this experimental study, the bacterial cells were incubated with 50, 100 and 250 µg mL-1 concentrations of C-PPy and irradiated with a 808-nm laser at two power densities of 0.5 and 1.0 W cm-2. CFU numbers were counted for the irradiated cells, and compared to an untreated sample (kept in dark). To explore the antibacterial properties and mechanism(s) of C-PPy, temperature increment, reactive oxygen species formation, and protein and DNA leakages were evaluated. Field emission scanning electron microscopy was also employed to investigate morphological changes in the bacterial cell structures.

RESULTS

The results showed that following C-PPy attachment to the bacteria surface, irradiation of near-infrared light resulted in a significant decrement in the bacterial cell viability due to photothermal lysis. Slightly increase in protein leakage and significantly increase intracellular reactive oxygen species (ROS) were observed in the bacteria upon treating with C-PPy.

CONCLUSION

Photo-ablation strategy is a new minimally invasive and inexpensive method without overdose risk manner for combat with bacteria.

Effect of methylene blue photodynamic therapy on human neutrophil functional responses

Photodynamic therapy (PDT) has become an emerging novel therapeutic approach for treating localized microbial infections, particularly those sustained by multidrug-resistant strains. Given the irreplaceable role played by professional phagocytes in limiting infections, such as polymorphonuclear neutrophils, any newly designed antimicrobial therapeutic approach must not interfere with their function. The present investigation presents a detailed analysis of the effect of PDT on the viability and several functional responses of human polymorphonuclear neutrophils loaded with methylene blue (MB), one of the more commonly used photosensitizers in antimicrobial PDT. Taking advantage of the use of a specifically-designed optical LED array for illuminating MB-loaded human polymorphonuclear neutrophils, a number of cell functions have been assayed under miniaturized, strictly controlled and reproducible experimental conditions. The major findings of this study are the following: (1) MB-PDT increases human neutrophils adhesion and does not modify myeloperoxidase release; (2) MB-PDT markedly enhances reactive oxygen species generation that is independent of superoxide-forming phagocytic oxidase and very likely ascribable to LED-dependent excitation of accumulated methylene blue; (3) MB-PDT almost abolishes human neutrophils candidacidal activity by hindering the engulfing machinery. This in vitro study may represent a valuable reference point for future research on PDT applications for treating localized microbial infections.

The Anti-Staphylococcal Potential of Ethanolic Polish Propolis Extracts

The principal objective of this study was to determine the anti-staphylococcal potential of ethanol extracts of propolis (EEPs). A total of 20 samples of propolis collected from apiaries located in different regions of Poland were used in the study. The two-fold broth microdilution method revealed some important differences in the antimicrobial activity of investigated EEPs. Up to the concentration of 4096 µg/mL no activity was observed against Gram-negative bacteria (E. coli and P. aeruginosa). Staphylococci exhibited much higher susceptibility. The highest efficiency observed for EEP12 and EEP20 (MIC values ranged between 32 and 256 µg/mL). However, the achievement of bactericidal effect usually required higher concentrations. In the case of clinical isolates of S. aureus MBC values for EEP12 and EEP20 ranged from 512 to 1024 µg/mL. The HPLC analysis revealed that these two products contained a higher concentration of flavonoids (flavonols, flavones, and flavanones) compared to other investigated EEPs. In checkerboard test, a synergistic anti-staphylococcal effect was observed for the action of EEP20 in combination with amikacin, kanamycin, gentamycin, tetracycline, and fusidic acid (all these antibiotics inhibit protein synthesis). Moreover, the investigated EEPs effectively eradicated staphylococcal biofilm. The obtained results clearly confirm the high anti-staphylococcal potential of propolis harvested in Polish apiaries.

Nonconventional Therapeutics against Staphylococcus aureus

Staphylococcus aureus is one of the most important human pathogens that is responsible for a variety of diseases ranging from skin and soft tissue infections to endocarditis and sepsis. In recent decades, the treatment of staphylococcal infections has become increasingly difficult as the prevalence of multi-drug resistant strains continues to rise. With increasing mortality rates and medical costs associated with drug resistant strains, there is an urgent need for alternative therapeutic options. Many innovative strategies for alternative drug development are being pursued, including disruption of biofilms, inhibition of virulence factor production, bacteriophage-derived antimicrobials, anti-staphylococcal vaccines, and light-based therapies. While many compounds and methods still need further study to determine their feasibility, some are quickly approaching clinical application and may be available in the near future.

Photodynamic therapy with chlorin-based photosensitizer at 405 nm: numerical, morphological, and clinical study

Employment of chlorin-based photosensitizers (PSs) provides additional advantages to photodynamic therapy (PDT) due to absorption peak around 405 nm allowing for superficial impact and efficient antimicrobial therapy. We report on the morphological and clinical study of the efficiency of PDT at 405 nm employing chlorin-based PS. Numerical studies demonstrated difference in the distribution of absorbed dose at 405 nm in comparison with traditionally employed wavelength of 660 nm and difference in the in-depth absorbed dose distribution for skin and mucous tissues. Morphological study was performed at the inner surface of rabbit ear with histological examinations at different periods after PDT procedure. Animal study revealed tissue reaction to PDT consisting in edema manifested most in 3 days after the procedure and neoangiogenesis. OCT diagnostics was confirmed by histological examination. Clinical study included antimicrobial PDT of pharynx chronic inflammatory diseases. It revealed no side effects or complications of the PDT procedure. Pharyngoscopy indicated reduction of inflammatory manifestations, and, in particular cases, hypervascularization was observed. Morphological changes were also detected in the course of monitoring, which are in agreement with pharyngoscopy results. Microbiologic study after PDT revealed no pathogenic bacteria; however, in particular cases, saprophytic flora was detected.

Combined Antimicrobial Activity of Photodynamic Inactivation and Antimicrobials-State of the Art

Antimicrobial photodynamic inactivation (aPDI) is a promising tool for the eradication of life-threatening pathogens with different profiles of resistance. This study presents the state-of-the-art published studies that have been dedicated to analyzing the bactericidal effects of combining aPDI and routinely applied antibiotics in in vitro (using biofilm and planktonic cultures) and in vivo experiments. Furthermore, the current paper reviews the methodology used to obtain the published data that describes the synergy between these antimicrobial approaches. The authors are convinced that even though the combined efficacy of aPDI and antimicrobials could be investigated with the wide range of methods, the use of a unified experimental methodology that is in agreement with antimicrobial susceptibility testing (AST) is required to investigate possible synergistic cooperation between aPDI and antimicrobials. Conclusions concerning the possible synergistic activity between the two treatments can be drawn only when appropriate assays are employed. It must be noticed that some of the described papers were just aimed at determination if combined treatments exert enhanced antibacterial outcome, without following the standard methodology to evaluate the synergistic effect, but in most of them (18 out of 27) authors indicated the existence of synergy between described antibacterial approaches. In general, the increase in bacterial inactivation was observed when both therapies were used in combination.

Antimicrobial Photodynamic Activity of Phthalocyanine Derivatives

Microbial pathogens have increasingly shown multidrug resistance posing a serious threat to the public health. Advances in technology are opening novel avenues for discovery of compounds that will mitigate the ever-increasing drug-resistant microbes. Use of photodynamic photosensitizer is one of the promising alternative approaches since they offer low risk of bacteria resistance as they use generated reactive oxygen species to kill the microbes. Phthalocyanine (Pc) is one such photosensitizer which has already shown promising antimicrobial photodynamic therapeutic properties. Previous studies have shown effectiveness of the Pc against Gram-positive bacteria. However, its effectiveness toward Gram-negative bacteria is limited by the impermeability of the bacteria’s outer membrane which is made up of lipopolysaccharides layer. The effectiveness of this photosensitizer is determined by its photophysical and photochemical properties such as singlet/triplet lifetimes, singlet oxygen quantum yields, and fluorescence quantum yield. Therefore, this review focuses on the recent significance advances on designing Pc that have this improved property by either conjugating with nanoparticles, quantum dots, functional groups in peripheral position, considering effect of cationic charge, and its position on the macrocycle.

Attaching NorA efflux pump inhibitors to methylene blue enhances antimicrobial photodynamic inactivation of Escherichia coli and Acinetobacter baumannii in vitro and in vivo

Resistance of bacteria to antibiotics is a public health concern worldwide due to the increasing failure of standard antibiotic therapies. Antimicrobial photodynamic inactivation (aPDI) is a promising non-antibiotic alternative for treating localized bacterial infections that uses non-toxic photosensitizers and harmless visible light to produce reactive oxygen species and kill microbes. Phenothiazinium photosensitizers like methylene blue (MB) and toluidine blue O are hydrophobic cations that are naturally expelled from bacterial cells by multidrug efflux pumps, which reduces their effectiveness. We recently reported the discovery of a NorA efflux pump inhibitor-methylene blue (EPI-MB) hybrid compound INF55-(Ac)en-MB that shows enhanced photodynamic inactivation of the Gram-positive bacterium methicillin-resistant Staphylococcus aureus (MRSA) relative to MB, both in vitro and in vivo. Here, we report the surprising observation that INF55-(Ac)en-MB and two related hybrids bearing the NorA efflux pump inhibitors INF55 and INF271 also show enhanced aPDI activity in vitro (relative to MB) against the Gram-negative bacteria Escherichia coli and Acinetobacter baumannii, despite neither species expressing the NorA pump. Two of the hybrids showed superior effects to MB in murine aPDI infection models. The findings motivate wider exploration of aPDI with EPI-MB hybrids against Gram-negative pathogens and more detailed studies into the molecular mechanisms underpinning their activity.

Antimicrobial photodynamic therapy-a promising treatment for prosthetic joint infections

Periprosthetic joint infection (PJI) is associated with high patient morbidity and a large financial cost. This study investigated Photodynamic Therapy (PDT) as a means of eradicating bacteria that cause PJI, using a laser with a 665-nm wavelength and methylene blue (MB) as the photosensitizer. The effectiveness of MB concentration on the growth inhibition of methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa and Acinetobacter baumannii was investigated. The effect of laser dose was also investigated and the optimized PDT method was used to investigate its bactericidal effect on species within planktonic culture and following the formation of a biofilm on polished titanium and hydroxyapatite coated titanium discs. Results showed that Staphylococci were eradicated at the lowest concentration of 0.1 mM methylene blue (MB). With P. aeruginosa and A. baumannii, increasing the MB concentration improved the bactericidal effect. When the laser dose was increased, results showed that the higher the power of the laser the more bacteria were eradicated with a laser power ≥ 35 J/cm² and an irradiance of 35 mW/cm², eradicating all S. epidermidis. The optimized PDT method had a significant bactericidal effect against planktonic MRSA and S. epidermidis compared to MB alone, laser alone, or control (no treatment). When biofilms were formed, PDT treatment had a significantly higher bactericidal effect than MB alone and laser alone for all species of bacteria investigated on the polished disc surfaces. P. aeruginosa grown in a biofilm was shown to be less sensitive to PDT when compared to Staphylococci, and a HA-coated surface reduced the effectiveness of PDT. This study demonstrated that PDT is effective for killing bacteria that cause PJI.

Purification, Characterization, and Mode of Action of Pentocin JL-1, a Novel Bacteriocin Isolated from Lactobacillus pentosus, against Drug-Resistant Staphylococcus aureus

Staphylococcus aureus and its drug-resistant strains, which threaten public health and food safety, are in need of effective control by biopreservatives. A novel bacteriocin, pentocin JL-1, produced by Lactobacillus pentosus that was isolated from the intestinal tract of Chiloscyllium punctatum, was purified by a four-step chromatographic process. Mass spectrometry based on MALDI-TOF indicated that pentocin JL-1 has a molecular mass of 2987.23 Da. Only six of the twenty-five amino acids could be identified by Edman degradation. This bacteriocin is thermostable and tolerates a pH range of 5–7. Also, it is sensitive to proteinase K, trypsin, pepsin, and alkaline protease. This bacteriocin has a broad inhibitory spectrum against both Gram-positive and Gram-negative strains and in particular is effective against multidrug-resistant S. aureus. Additionally, we showed that the cell membrane is the target of pentocin JL-1 against methicillin-resistant S. aureus (MRSA), causing a loss of proton motive force. Furthermore, pentocin JL-1 has a drastic impact on the structure and integrity of MRSA cells. These results suggest that pentocin JL-1 has potential as a biopreservative in the food industry.

Enhanced Photobactericidal and Targeting Properties of a Cationic Porphyrin following the Attachment of Polymyxin B

A novel compound consisting of a cationic porphyrin covalently attached to a derivative of polymyxin B has been synthesized and presents enhanced activity and targeting properties compared to the usual cationic porphyrins recognized as efficient photosensitizers in photodynamic antimicrobial chemotherapy (PACT). A synthesis pathway was established to preserve the bactericidal activity of the peptide. Accordingly, the N-terminal amino acid (l-2,4-diaminobutyric acid) of polymyxin B (PMB) was switched for a cysteine residue. Then, the resulting derivative of PMB was covalently bound to 5-(4-aminophenyl)-10,15,20-tri(4-N-methylpyridyl)-21H,23H-porphyrin using a thiol-maleimide "click" coupling. The peptide-coupled photosensitizer has demonstrated an improved PACT efficiency compared to the cationic porphyrin alone. This enhancement has been observed against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli in particular. Flow cytometry analyses and confocal imaging microscopy demonstrated that the porphyrin-peptide conjugate selectively adhered to the cell walls of either Gram-positive or Gram-negative bacteria, thus justifying the damages induced by singlet oxygen production.

Poly(carboxylic acid)-Cyclodextrin/Anionic Porphyrin Finished Fabrics as Photosensitizer Releasers for Antimicrobial Photodynamic Therapy

In the development of new antibacterial therapeutic approaches to fight multidrug-resistant bacteria, antimicrobial photodynamic therapy (aPDT) represents a well-known alternative to treat local infections caused by different microorganisms. Here we present a polypropylene (PP) fabric finished with citrate-hydroxypropyl-βCD polymer (PP-CD) entrapping the tetra-anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine (TPPS) as photosensitizer-eluting scaffold (PP-CD/TPPS) for aPDT. The concept is based on host-guest complexation of porphyrin in the cavities of CDs immobilized on the PP fibers, followed by its sustained and controlled delivery in release medium and simultaneous photoinactivation of microorganisms. Morphology of fabric was characterized by optical (OM) and scanning electron microscopies (SEM). Optical properties were investigated by UV-vis absorption, steady- and time-resolved fluorescence emission spectroscopy. X-ray photoelectron spectroscopy (XPS) and FT-IR revealed the surface chemical composition and the distribution map of the molecular components on the fabric, respectively. Direct ¹O₂ determination allowed to assess the potential photodynamic activity of the fabric. Release kinetics of TPPS in physiological conditions pointed out the role of the CD cavity to control the TPPS elution. Photoantimicrobial activity of the porphyrin-loaded textile was investigated against both Gram-positive Staphylococcus aureus ATCC 29213 (S. aureus) and Gram-negative Pseudomonas aeruginosa ATCC 27853 (P. aeruginosa). Optical microscopy coupled with UV-vis extinction and fluorescence spectra aim to ascertain the uptake of TPPS to S. aureus bacterial cells. Finally, PP-CD/TPPS fabric-treated S. aureus cells were photokilled of 99.98%. Moreover, low adhesion of S. aureus cells on textile was established. Conversely, no photodamage of fabric-treated P. aeruginosa cells was observed, together with their satisfying adhesion.

Improvement of Antibacterial Efficacy Through Synergistic Effect in Photodynamic Therapy Based on Thiazinium Chromophores Against Planktonic and Biofilm-Associated Periodontopathogens

OBJECTIVE

Aim of the study was to improve the antibacterial efficacy of toluidine blue (TBO)/methylene blue (MB)-mediated photodynamic systems with light-emitting diode (LED) or laser irradiation administered to planktonic and biofilm-associated periodontopathogens.

BACKGROUND DATA

Antibacterial photodynamic therapy (PDT) is a common, noninvasive adjunctive clinical method to inactivate microorganisms. So far, the disadvantage of this method has been its limited effectiveness in eliminating pathogens.

METHODS

An anaerobic cocktail consisting of six representative periodontal pathogens was prepared as initial culture for planktonic samples and biofilms grown on human tooth slides. Both types of microbial samples were exposed to three commercial photodynamic systems (PDT1: TBO, 630 nm LED, PDT2: TBO, 635 nm laser, PDT3: MB, 665 nm laser) in conventional and a new modified approach (PDT^plus) based on the use of an oxygen supplement (photosensitizer+hydrogen peroxide). The microbial viability was characterized by bacterial growth [colony forming units (CFU)], total bacterial cell counts, and microbial vitality. Statistical data analysis was performed using 95% confidence intervals (ANOVA) and post hoc Tukey's test (p < 0.05).

RESULTS

The modified PDT^plus showed the highest statistically significant synergistic antimicrobial activity for TBO-based systems evidenced by a CFU reduction of 9 log₁₀ units to 0 for planktonic pathogens and a 4 log₁₀ CFU reduction for biofilm bacteria. The MB-based PDT^plus was superior mainly against biofilm pathogens. By comparison, the default TBO-based PDT achieved colony growth reductions of 2 and 1 log₁₀ units concerning planktonic and biofilm cells.

CONCLUSIONS

Compared to conventional PDT, PDT^plus showed superior antibacterial efficacy based on its synergistic effect, promising vast application possibilities.