Synergistic in vitro effects of indocyanine green and ethylenediamine tetraacetate-mediated antimicrobial photodynamic therapy combined with antibiotics for resistant bacterial biofilms in diabetic foot infection

Alkylated EDTA potentiates antibacterial photodynamic activity of protoporphyrin

Antibiotic resistance has garnered significant attention due to the scarcity of new antibiotics in development. Protoporphyrin IX (PpIX)-mediated photodynamic therapy shows promise as a novel antibacterial strategy, serving as an alternative to antibiotics. However, the poor solubility of PpIX and its tendency to aggregate greatly hinder its photodynamic efficacy. In this study, we demonstrate that alkylated EDTA derivatives (aEDTA), particularly C14-EDTA, can enhance the solubility of PpIX by facilitating its dispersion in aqueous solutions. The combination of C14-EDTA and PpIX exhibits potent antibacterial activity against Staphylococcus aureus (S. aureus) when exposed to LED light irradiation. Furthermore, this combination effectively eradicates S. aureus biofilms, which are known to be strongly resistant to antibiotics, and demonstrates high therapeutic efficacy in an animal model of infected ulcers. Mechanistic studies reveal that C14-EDTA can disrupt PpIX crystallization, increase bacterial membrane permeability and sequester divalent cations, thereby improving the accumulation of PpIX in bacteria. This, in turn, enhances reactive oxygen species (ROS) production and the antibacterial photodynamic activity. Overall, this effective strategy holds great promise in combating antibiotic-resistant strains.

The Miraculous Diagnostic Role of Indocyanine Green in a Diabetic Foot Ulcer: A Rare Case Report

Diabetes is a chronic metabolic disorder characterized by elevated levels of glucose in the blood. This causes small nerve polyneuropathy resulting in diabetic foot ulcers. A diabetic foot ulcer is an open sore or wound that develops as a result of chronic diabetes. Indocyanine green angiography (ICGA) near-infrared (NIR) can provide real-time visualization of blood flow within the microvasculature of the underlying organ. Here, we discuss a 63-year-old patient who came with a diabetic foot ulcer over his right great toe. His blood glucose level was 208 mg/dl. He drinks alcohol occasionally and smokes regularly. The tissue perfusion of his right foot was checked using the indocyanine green dye, after which orthopedic surgeons were consulted, and the gangrenous part was amputated.

Photodynamic therapy for ESKAPE pathogens: An emerging approach to combat antimicrobial resistance (AMR)

The increase in antimicrobial resistance, particularly in ESKAPE pathogens, has resulted in the dire need for new therapeutic approaches. ESKAPE is an acronym for a group of bacteria that are responsible for a majority of nosocomial and community acquired infections. The acronym stands for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species. These pathogens are known for their ability to develop resistance to multiple antibiotics, making them difficult to treat thus posing a significant threat to public health. In light of the alarming consequences of antimicrobial resistance, it has been estimated that, in the absence of a substantial increase in the rate of development of new effective drugs, the number of casualties related to these infections will increase from about 700,000 in 2016 up to nearly 10,000,000 in 2050 [1]. One potential strategy to treat these pathogens is photodynamic therapy (PDT). In the early 20th century, Oscar Raab observed the phototoxicity of acridine red against Paramecium caudatum, while Tappenier and Jesionek demonstrated the photodynamic effects of eosin for treating cutaneous diseases. These discoveries laid the foundation for Photodynamic Therapy (PDT), which utilizes a non-toxic photosensitizer (PS) followed by targeted light irradiation for treatment [2]. PDT involves the use of a photosensitizer, a light source, and oxygen to eliminate highly active infectious pathogens such as bacteria, viruses, and fungi. PDT is known to possess several advantages including localized treatment and fewer side effects. Various photosensitizers and light sources have been assessed in different strains, showing promising results suggesting PDT to be a promising potential treatment option. PDT utilizes PS compounds with suitable light absorption that showcase effective results against the pathogens in vitro and in vivo, including BODIPY derivatives, Methylene Blue, and other dyes like porphyrin derivatives, phthalocyanines, indole derivatives, Photophrin, etc., inhibiting the growth of infections, for both in planktonic cells and in biofilms. Combination of PDT with other therapies like efflux pump inhibitors or quorum sensing inhibitors has also proven to be efficacious. However, this domain further needs to be assessed before it reaches the society.

Medical Applications and Advancement of Near Infrared Photosensitive Indocyanine Green Molecules

Indocyanine green (ICG) is an important kind of near infrared (NIR) photosensitive molecules for PTT/PDT therapy as well as imaging. When exposed to NIR light, ICG can produce reactive oxygen species (ROS), which can kill cancer cells and pathogenic bacteria. Moreover, the absorbed light can also be converted into heat by ICG molecules to eliminate cancer cells. In addition, it performs exceptionally well in optical imaging-guided tumor therapy and antimicrobial therapy due to its deeper tissue penetration and low photobleaching properties in the near-infrared region compared to other dyes. In order to solve the problems of water and optical stability and multi-function problem of ICG molecules, composite nanomaterials based on ICG have been designed and widely used, especially in the fields of tumors and sterilization. So far, ICG molecules and their composite materials have become one of the most famous infrared sensitive materials. However, there have been no corresponding review articles focused on ICG molecules. In this review, the molecular structure and properties of ICG, composite material design, and near-infrared light- triggered anti-tumor, and antibacterial, and clinical applications are reviewed in detail, which of great significance for related research.

Photodynamic Therapy, Probiotics, Acetic Acid, and Essential Oil in the Treatment of Chronic Wounds Infected with Pseudomonas aeruginosa

As a prevalent medical problem that burdens millions of patients across the world, chronic wounds pose a challenge to the healthcare system. These wounds, often existing as a comorbidity, are vulnerable to infections. Consequently, infections hinder the healing process and complicate clinical management and treatment. While antibiotic drugs remain a popular treatment for infected chronic wounds, the recent rise of antibiotic-resistant strains has hastened the need for alternative treatments. Future impacts of chronic wounds are likely to increase with aging populations and growing obesity rates. With the need for more effective novel treatments, promising research into various wound therapies has seen an increased demand. This review summarizes photodynamic therapy, probiotics, acetic acid, and essential oil studies as developing antibiotic-free treatments for chronic wounds infected with Pseudomonas aeruginosa. Clinicians may find this review informative by gaining a better understanding of the state of current research into various antibiotic-free treatments. Furthermore. this review provides clinical significance, as clinicians may seek to implement photodynamic therapy, probiotics, acetic acid, or essential oils into their own practice.

Photodynamic therapy for infected foot ulcers in people with diabetes mellitus: a systematic review

BACKGROUND

Ulceration of the feet in patients with diabetes is a frequent complication that increases morbidity, mortality, hospitalization, treatment costs, and non-traumatic amputations.

OBJECTIVE

To present a systematic review of the treatment of patients with diabetes mellitus and infected foot ulcers using photodynamic therapy.

DESIGN AND SETTING

A systematic review was performed in the postgraduate program in nursing at the Universidade da Integração Internacional da Lusofonia Afro-Brasileira, Ceará, Brazil.

METHODS

PubMed, CINAHL, Web of Science, EMBASE, Cochrane Library, Scopus, and LILACS databases were screened. The methodological quality, risk of bias, and quality of evidence of each study were assessed. Review Manager was used for the meta-analysis.

RESULTS

Four studies were included. They highlighted significantly better outcomes in patient groups treated with photodynamic therapy than those in the control groups that were treated with topical collagenase and chloramphenicol (P = 0.036), absorbent (P < 0.001), or dry covers (P = 0.002). Significant improvements were noted in terms of the microbial load in the ulcers and tissue repair, with a reported reduction in the need for amputation by up to 35 times. Photodynamic therapy resulted in significantly better outcomes between the experimental and control groups (P = 0.04).

CONCLUSION

Photodynamic therapy is significantly more effective in treating infected foot ulcers than standard therapies.

SYSTEMATIC REVIEW REGISTRATION

International Prospective Register of Systematic Reviews (PROSPERO) - CRD42020214187, https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=214187.

Bacteria Wear ICG Clothes for Rapid Detection of Intracranial Infection in Patients After Neurosurgery and Photothermal Antibacterial Therapy Against Streptococcus Mutans

Bacterial infection is one of the most serious physiological conditions threatening human health. There is an increasing demand for more effective bacterial diagnosis and treatment through non-invasive approaches. Among current antibacterial strategies of non-invasive approaches, photothermal antibacterial therapy (PTAT) has pronounced advantages with properties of minor damage to normal tissue and little chance to trigger antimicrobial resistance. Therefore, we developed a fast and simple strategy that integrated the sensitive detection and photothermal therapy of bacteria by measuring adenosine triphosphate (ATP) bioluminescence following targeted photothermal lysis. First, 3-azido-d-alanine (d-AzAla) is selectively integrated into the cell walls of bacteria, photosensitizer dibenzocyclooctyne, and double sulfonic acid-modified indocyanine green (sulfo-DBCO-ICG) are subsequently designed to react with the modified bacteria through in vivo click chemistry. Next, the sulfo-DBCO-ICG modified bacteria under irradiation of 808 nm near-infrared laser was immediately detected by ATP bioluminescence following targeted photothermal lysis and even the number of bacteria on the infected tissue can be significantly reduced through PTAT. This method has demonstrated the ability to detect the presence of the bacteria for ATP value in 32 clinical samples. As a result, the ATP value over of 100 confirmed the presence of bacteria in clinical samples for 22 patients undergoing craniotomy and ten otitis media patients. Overall, this study paves a brand new avenue to facile diagnosis and a treatment platform for clinical bacterial infections.

Synergistic effect of TONS504-mediated photodynamic antimicrobial chemotherapy and additives widely contained in ophthalmic solutions: benzalkonium chloride and ethylenediaminetetraacetic acid

TONS504 (C₅₁H₅₈N₈O₅I₂), a chlorine derivative, effectively generates singlet oxygen by light activation and exhibits photodynamic antimicrobial effects (PAEs) on various pathogens. However, this photosensitizer has some limitations: a high tendency to self-aggregate and a relatively weak PAE for Gram-negative bacteria compared with Gram-positive bacteria. To overcome these limitations, the present study investigated the synergistic effects of the PAE of TONS504 and two additives commonly contained in ophthalmic solutions: benzalkonium chloride (BAC) or ethylenediaminetetraacetic acid (EDTA). Staphylococcus aureus and Pseudomonas aeruginosa were exposed to TONS504 and/or each additive. Photodynamic antimicrobial chemotherapy was performed with light irradiation centered at a wavelength of 665 nm with a total light energy of 30 J/cm². Following incubation, the number of colonies formed was counted. Additionally, we examined the inhibitory effects of the additives on TONS504 self-aggregation by observing its absorption spectrum. Consequently, the PAEs of TONS504 on S. aureus were enhanced by both additives, and BAC displayed stronger synergistic effects on the bacteria than EDTA. By contrast, only EDTA increased the PAE on P. aeruginosa. The peak of the TONS504 absorption spectrum shifted to a longer wave length and the absorbance increased in the presence of BAC, suggesting that BAC inhibited the self-aggregation of the photosensitizer. In conclusion, the combination of BAC or EDTA and TONS504-mediated photodynamic antimicrobial chemotherapy exhibits a synergistic antimicrobial effect on S. aureus and P. aeruginosa. The optimal additive to enhance the PAE may differ between bacterial strains.

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.

Biofilm Formation by Pathogenic Bacteria: Applying a Staphylococcus aureus Model to Appraise Potential Targets for Therapeutic Intervention

Carried in the nasal passages by up to 30% of humans, Staphylococcus aureus is recognized to be a successful opportunistic pathogen. It is a frequent cause of infections of the upper respiratory tract, including sinusitis, and of the skin, typically abscesses, as well as of food poisoning and medical device contamination. The antimicrobial resistance of such, often chronic, health conditions is underpinned by the unique structure of bacterial biofilm, which is the focus of increasing research to try to overcome this serious public health challenge. Due to the protective barrier of an exopolysaccharide matrix, bacteria that are embedded within biofilm are highly resistant both to an infected individual’s immune response and to any treating antibiotics. An in-depth appraisal of the stepwise progression of biofilm formation by S. aureus, used as a model infection for all cases of bacterial antibiotic resistance, has enhanced understanding of this complicated microscopic structure and served to highlight possible intervention targets for both patient cure and community infection control. While antibiotic therapy offers a practical means of treatment and prevention, the most favorable results are achieved in combination with other methods. This review provides an overview of S. aureus biofilm development, outlines the current range of anti-biofilm agents that are used against each stage and summarizes their relative merits.

Applications of Antimicrobial Photodynamic Therapy against Bacterial Biofilms

Antimicrobial photodynamic therapy and allied photodynamic antimicrobial chemotherapy have shown remarkable activity against bacterial pathogens in both planktonic and biofilm forms. There has been little or no resistance development against antimicrobial photodynamic therapy. Furthermore, recent developments in therapies that involve antimicrobial photodynamic therapy in combination with photothermal hyperthermia therapy, magnetic hyperthermia therapy, antibiotic chemotherapy and cold atmospheric pressure plasma therapy have shown additive and synergistic enhancement of its efficacy. This paper reviews applications of antimicrobial photodynamic therapy and non-invasive combination therapies often used with it, including sonodynamic therapy and nanozyme enhanced photodynamic therapy. The antimicrobial and antibiofilm mechanisms are discussed. This review proposes that these technologies have a great potential to overcome the bacterial resistance associated with bacterial biofilm formation.

Recent Developments in Nitric Oxide Donors and Delivery for Antimicrobial and Anti-Biofilm Applications

The use of nitric oxide (NO) is emerging as a promising, novel approach for the treatment of antibiotic resistant bacteria and biofilm infections. Depending on the concentration, NO can induce biofilm dispersal, increase bacteria susceptibility to antibiotic treatment, and induce cell damage or cell death via the formation of reactive oxygen or reactive nitrogen species. The use of NO is, however, limited by its reactivity, which can affect NO delivery to its target site and result in off-target effects. To overcome these issues, and enable spatial or temporal control over NO release, various strategies for the design of NO-releasing materials, including the incorporation of photo-activable, charge-switchable, or bacteria-targeting groups, have been developed. Other strategies have focused on increased NO storage and delivery by encapsulation or conjugation of NO donors within a single polymeric framework. This review compiles recent developments in NO drugs and NO-releasing materials designed for applications in antimicrobial or anti-biofilm treatment and discusses limitations and variability in biological responses in response to the use of NO for bacterial eradiation.

pH-switchable nanozyme cascade catalysis: a strategy for spatial-temporal modulation of pathological wound microenvironment to rescue stalled healing in diabetic ulcer

The management of diabetic ulcer (DU) to rescue stalled wound healing remains a paramount clinical challenge due to the spatially and temporally coupled pathological wound microenvironment that features hyperglycemia, biofilm infection, hypoxia and excessive oxidative stress. Here we present a pH-switchable nanozyme cascade catalysis (PNCC) strategy for spatial–temporal modulation of pathological wound microenvironment to rescue stalled healing in DU. The PNCC is demonstrated by employing the nanozyme of clinically approved iron oxide nanoparticles coated with a shell of glucose oxidase (Fe₃O₄-GOx). The Fe₃O₄-GOx possesses intrinsic glucose oxidase (GOx), catalase (CAT) and peroxidase (POD)-like activities, and can catalyze pH-switchable glucose-initiated GOx/POD and GOx/CAT cascade reaction in acidic and neutral environment, respectively. Specifically, the GOx/POD cascade reaction generating consecutive fluxes of toxic hydroxyl radical spatially targets the acidic biofilm (pH ~ 5.5), and eradicates biofilm to shorten the inflammatory phase and initiate normal wound healing processes. Furthermore, the GOx/CAT cascade reaction producing consecutive fluxes of oxygen spatially targets the neutral wound tissue, and accelerates the proliferation and remodeling phases of wound healing by addressing the issues of hyperglycemia, hypoxia, and excessive oxidative stress. The shortened inflammatory phase temporally coupled with accelerated proliferation and remodeling phases significantly speed up the normal orchestrated wound-healing cascades. Remarkably, this Fe₃O₄-GOx-instructed spatial–temporal remodeling of DU microenvironment enables complete re-epithelialization of biofilm-infected wound in diabetic mice within 15 days while minimizing toxicity to normal tissues, exerting great transformation potential in clinical DU management. The proposed PNCC concept offers a new perspective for complex pathological microenvironment remodeling, and may provide a powerful modality for the treatment of microenvironment-associated diseases.

Optical clearing of tissues: Issues of antimicrobial phototherapy and drug delivery

This review presents principles and novelties in the field of tissue optical clearing (TOC) technology, as well as application for optical monitoring of drug delivery and effective antimicrobial phototherapy. TOC is based on altering the optical properties of tissue through the introduction of immersion optical cleaning agents (OCA), which impregnate the tissue of interest. We also analyze various methods and kinetics of delivery of photodynamic agents, nanoantibiotics and their mixtures with OCAs into the tissue depth in the context of antimicrobial and antifungal phototherapy. In vitro and in vivo studies of antimicrobial phototherapies, such as photodynamic, photothermal plasmonic and photocatalytic, are summarized, and the prospects of a new TOC technology for effective killing of pathogens are discussed.

Using systems biology approaches to identify signalling pathways activated during chronic wound initiation

Chronic wounds are a significant health problem worldwide. However, nothing is known about how chronic wounds initiate and develop. Here we use a chronic wound model in diabetic mice and a Systems Biology Approach using nanoString nCounter technology and weighted gene correlation network analysis (WGCNA), with tissues collected at 6, 12, 24 and 48 h post-wounding, to identify metabolic signalling pathways involved in initiation of chronicity. Normalized counts obtained from the nanoString nCounter Mouse Metabolic Panel were used for the WGCNA, which groups genes into co-expression modules to visualize the correlation network. Genes with significant module membership and gene trait significance (p < 0.05) were used to identify signalling pathways that are important for the development of chronicity. The pathway analysis using the Reactome database showed stabilization of PTEN, which down-regulates PI3K/AKT1, which in turn down-regulates Nrf2, as shown by ELISA, thus disabling antioxidant production, resulting in high oxidative stress levels. We find that pathways involved in inflammation, including those that generate pro-inflammatory lipids derived from arachidonic acid metabolism, IFNγ and catecholamines, occur. Moreover, HIF3α is over-expressed, potentially blocking Hif1α and preventing activation of growth factors and cytokines that promote granulation tissue formation. We also find that FGF1 is under-expressed, while thrombospondin-1 is over-expressed, resulting in decreased angiogenesis, a process that is critical for healing. Finally, enzymes involved in glycolysis are down-regulated, resulting in decreased production of pyruvate, a molecule critical for ATP production, leading to extensive cell death and wound paralysis. These findings offer new avenues of study that may lead to the development of novel treatments of CW to be administered right after debridement.

Biofilms in Diabetic Foot Ulcers: Impact, Risk Factors and Control Strategies

Diabetic foot ulcers (DFUs) are a serious complication from diabetes mellitus, with a huge economic, social and psychological impact on the patients' life. One of the main reasons why DFUs are so difficult to heal is related to the presence of biofilms. Biofilms promote wound inflammation and a remarkable lack of response to host defences/treatment options, which can lead to disease progression and chronicity. In fact, appropriate treatment for the elimination of these microbial communities can prevent the disease evolution and, in some cases, even avoid more serious outcomes, such as amputation or death. However, the detection of biofilm-associated DFUs is difficult due to the lack of methods for diagnostics in clinical settings. In this review, the current knowledge on the involvement of biofilms in DFUs is discussed, as well as how the surrounding environment influences biofilm formation and regulation, along with its clinical implications. A special focus is also given to biofilm-associated DFU diagnosis and therapeutic strategies. An overview on promising alternative therapeutics is provided and an algorithm considering biofilm detection and treatment is proposed.

Effects of curcumin-mediated antimicrobial photodynamic therapy associated to different chelators against Enterococcus faecalis biofilms

BACKGROUND

The aim of this study was to evaluate curcumin-mediated antimicrobial photodynamic therapy (aPDT) action combined or not with ethylenediaminetetraacetic acid (EDTA) and hydroxyethylidene bisphosphonate (HEBP) on Enterococcus faecalis biofilms.

METHODS

Enterococcus faecalis biofilms were grown on dentin bovine discs in brain heart infusion (BHI) medium with 1% glucose, in aerobic conditions at 37°C for 7 days. Then, they were randomly distributed to one of experimental conditions, as follows: control, 75 J.cm^-2 LED, 600 μmol.L^-1 curcumin, 17% EDTA, 18% HEBP, 600 μmol.L^-1 curcumin plus 75 J.cm^-2 LED, 600 μmol.L^-1 curcumin plus 17% EDTA, 600 μmol.L^-1 curcumin plus 18% HEBP, 600 μmol.L^-1 curcumin plus 17% EDTA and 75 J.cm^-2 LED or 600 μmol.L^-1 curcumin plus 18% HEBP and 75 J.cm^-2 LED. The viability of microorganisms and the vitality of biofilms were determined by colony forming unit counts and confocal scanning laser microscopy (CSLM), respectively. Statistical analysis was conducted by Kruskal Wallis and Dunn's post-hoc tests (α = 0.05).

RESULTS

The results showed that all combinations of aPDT with chelators significantly reduced the viability of microbial cells and the vitality of biofilms in comparison to control, even when considering deeper layers of biofilms.

CONCLUSION

The combination of curcumin with EDTA and HEBP similarly improved the effect of aPDT on E. faecalis biofilms.

Photodynamic therapy for treatment of Staphylococcus aureus infections

BACKGROUND

Staphylococcus aureus is a Gram-positive spherical bacterium that commonly causes various infections which can range from superficial to life-threatening. Hospital strains of S. aureus are often resistant to antibiotics, which has made their treatment difficult in recent decades. Other therapeutic alternatives have been postulated to overcome the drawbacks of antibiotic multi-resistance. Of these, photodynamic therapy (PDT) is a promising approach to address the notable shortage of new active antibiotics against multidrug-resistant S. aureus. PDT combines the use of a photosensitizer agent, light, and oxygen to eradicate pathogenic microorganisms. Through a systematic analysis of published results, this work aims to verify the usefulness of applying PDT in treating multidrug-resistant S.aureus infections.

METHODS

This review was based on a bibliographic search in various databases and the analysis of relevant publications.

RESULTS

There is currently a large body of evidence demonstrating the efficacy of photodynamic therapy in eliminating S.aureus strains. Both biofilm-producing strains, as well as multidrug-resistant strains.

CONCLUSION

We conclude that there is sufficient scientific evidence that PDT is a useful adjunct to traditional antibiotic therapy for treating S. aureus infections. Clinical application through appropriate trials should be introduced to further define optimal treatment protocols, safety and efficay.

Engineered photo-chemical therapeutic nanocomposites provide effective antibiofilm and microbicidal activities against bacterial infections in porous devices

Today, prosthetic joint infection (PJI) is still a relatively rare but devastating complication following total hip and/or knee arthroplasty. The treatment of PJI is difficult due to a number of obstacles, such as microbial drug resistance, biofilm protection, and insufficient immune activity, which dramatically diminish the cure rate of PJI to <50%. To efficiently eradicate the bacteria hiding in the implant, photo-chemical joint antibacterial therapeutics based on indocyanine green (ICG) and rifampicin (RIF) co-loaded PLGA nanoparticles (IRPNPs) were developed in this study. The IRPNPs were first characterized as a spherical nanostructure with a size of 266 ± 18.2 nm and a surface charge of -28 ± 1.6 mV. In comparison with freely dissolved ICG, the IRPNPs may confer enhanced thermal stability to the encapsulated ICG and are able to provide a comparable hyperthermic effect and increased production of singlet oxygen under 808 nm near infrared (NIR) exposure with an intensity of 6 W cm-2. Based on the spectrophotometric analysis, the IRPNPs with ≥20-/3.52 μM ICG/RIF were able to provide remarkable antibiofilm and antimicrobial effects against bacteria in a porous silicon bead upon NIR exposure in vitro. Through the analysis of the microbial population index in an animal study, ≥70% Staphylococcus capitis subsp. urealyticus grown in a porous silicon bead in vivo can be successfully eliminated without organ damage or inflammatory lesions around the implant by using IRPNPs + NIR irradiation every 72 h for 9 days. The resulting bactericidal efficacy was approximately three-fold higher than that resulting from using an equal amount of free RIF alone. Taken together, we anticipate that IRPNP-mediated photochemotherapy can serve as a feasible antibacterial approach for PJI treatment in the clinic.

Combined Addition of Ethanol and Ethylenediaminetetraacetic Acid Enhances Antibacterial and Antibiofilm Effects in Methylene Blue-Mediated Photodynamic Treatment against Pseudomonas aeruginosa In Vitro

Antimicrobial photodynamic treatment (aPDT) for infection with drug-resistant bacteria has received much attention. For P. aeruginosa, however, efficient formation of biofilms and the nature of Gram-negative bacteria often limit the efficacy of aPDT. In this study, we investigated the effects of ethanol and ethylenediaminetetraacetic acid (EDTA) as additives on bacterial viability, biofilm biomass, and structures of bacteria and biofilms in methylene blue (MB)-mediated aPDT in vitro. Matured P. aeruginosa biofilms were incubated with 32-µm MB solutions with different concentrations of additives and then illuminated with 665-nm light from an LED array. The combined addition of 10% ethanol and 10 mm EDTA to MB resulted in significantly greater bactericidal effects than those of MB alone and of MB with 10% ethanol or 10 mm EDTA. Crystal violet assays showed significant reductions in biofilm biomass by aPDT with addition of both ethanol and EDTA compared to that in the case of aPDT with MB alone. Scanning electron microscopy showed broken bacterial cells and reduction in the cell density and amount of biofilm under those conditions. Ethanol addition alone did not improve aPDT efficacy. Reduced amount of biofilm by EDTA addition would have improved the transportation of MB and ethanol to bacteria.

Photodynamic therapy to control microbial biofilms

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

Photodynamic antimicrobial chemotherapy using indocyanine green in experimentally induced intraoral ulcers in rats

BACKGROUND

Photodynamic antimicrobial chemotherapy (PACT) is a promising modality for eradication of microorganisms from the wound. This study aimed to investigate the effectiveness of PACT using indocyanine green (ICG) for reduction of bacterial load of oral ulcers in rats and its impact on the healing process.

METHODS

In this experimental study, 50 adult male Sprague Dawley rats were recruited. Oral ulcers were surgically made on the left cheek mucosa, and animals were randomly assigned into five groups (n = 10). Wound site in groups 1, 2, and 3 was irrigated with the sterile saline (0.9%), chlorhexidine (CHX; 0.2%), and ICG solutions (1 mg/mL), respectively. Group 4 was exposed to laser irradiation using 810 nm diode laser on continuous-wave mode for 30 seconds (fluence: 55 J/cm² , power: 300 mW, spot size: 4.5 mm). In group 5, PACT was performed using topical application of ICG followed by laser irradiation in the same way as the previous group. Bacterial load of oral ulcers was assessed before and after each treatment modality. Besides, rats were sacrificed on the 5th day post ulceration and histological features of healing were evaluated.

RESULTS

Bacterial load was significantly reduced merely in the PACT-ICG-treated group by one log (P < .0001). Animals in the PACT-ICG-treated group also showed an accelerated healing in comparison with others on the 5th day of an experiment.

CONCLUSION

Photodynamic antimicrobial chemotherapy using topical application of ICG has a potential to reduce the bacterial load of oral ulcers and accelerate wound repair. Therefore, it can be considered as an alternative to currently available modalities for wound management.

Photodynamic antimicrobial chemotherapy in mice with Pseudomonas aeruginosa-infected wounds

This study examined the antibacterial effect of protoporphyrin IX–ethylenediamine derivative (PPIX-ED)–mediated photodynamic antimicrobial chemotherapy (PPIX-ED-PACT) against Pseudomonas aeruginosa in vitro and in vivo. PPIX-ED potently inhibited the growth of Pseudomonas aeruginosa by inducing reactive oxygen species production via photoactivation. Atomic force microscopy revealed that PPIX-ED-PACT induced the leakage of bacterial content by degrading the bacterial membrane and wall. As revealed using acridine orange/ethidium bromide staining, PPIX-ED-PACT altered the permeability of the bacterial membrane. In addition, the antibacterial effect of PPIX-ED-PACT was demonstrated in an in vivo model of P. aeruginosa-infected wounds. PPIX-ED (100 μM) decreased the number of P. aeruginosa colony-forming units by 4.2 log₁₀. Moreover, histological analysis illustrated that the wound healing rate was 98% on day 14 after treatment, which was 10% higher than that in the control group. According to the present findings, PPIX-ED-PACT can effectively inhibit the growth of P. aeruginosa in vitro and in vivo.

Innovative Strategies Toward the Disassembly of the EPS Matrix in Bacterial Biofilms

Bacterial biofilms represent a major concern at a worldwide level due to the high demand for implantable medical devices and the rising numbers of bacterial resistance. The complex structure of the extracellular polymeric substances (EPS) matrix plays a major role in this phenomenon, since it protects bacteria from antibiotics, avoiding drug penetration at bactericidal concentrations. Besides, this structure promotes bacterial cells to adopt a dormant lifestyle, becoming less susceptible to antibacterial agents. Currently, the available treatment for biofilm-related infections consists in the administration of conventional antibiotics at high doses for a long-term period. However, this treatment lacks efficiency against mature biofilms and for implant-associated biofilms it may be necessary to remove the medical device. Thus, biofilm-related infections represent an economical burden for the healthcare systems. New strategies focusing on the matrix are being highlighted as alternative therapies to eradicate biofilms. Here, we outline reported matrix disruptive agents, nanocarriers, and technologies, such as application of magnetic fields, photodynamic therapy, and ultrasounds, that have been under investigation to disrupt the EPS matrix of clinically relevant bacterial biofilms. In an ideal therapy, a synergistic effect between antibiotics and the explored innovated strategies is aimed to completely eradicate biofilms and avoid antimicrobial resistance phenomena.

Inhibition of methicillin-resistant Staphylococcus aureus (MRSA) biofilm by cationic poly (D, L-lactide-co-glycolide) nanoparticles

The emergent need for new treatment methods for multi-drug resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) has focused attention on novel potential tools like nanoparticles (NPs). In the present study, a drug-free cationic nanoparticles (CNPs) system was developed and its anti-MRSA effects were firstly investigated. The results showed that CNPs (261.7 nm, 26.1 mv) showed time- and concentration-dependent activity against MRSA growth, killing ∼ 90% of planktonic bacterial cells in 3 h at 400 μg ml^-1, and completely inhibiting biofilm formation at 1000 μg ml^-1. Moreover, CNPs at 400 μg ml^-1 reduced the minimum inhibitory concentration (MIC) of vancomycin on inhibition of planktonic MRSA growth (∼ 25%) and biofilm formation (∼ 50%). The CNPs-bacteria interaction force was up to 22 nN. Overall, these data suggest that CNPs have a good potential in clinical applications for the prevention and treatment of MRSA infection.

Synergistic antimicrobial effects of photodynamic antimicrobial chemotherapy and gentamicin on Staphylococcus aureus and multidrug-resistant Staphylococcus aureus

BACKGROUND

Bacterial resistance to antibiotics is generally increasing, which has become a great challenge for treating infectious diseases caused by microbes. Photodynamic antibacterial chemotherapy (PACT) has been considered as a promising method for inactivating bacteria. The combination of antimicrobial agent with PACT may provide efficient way against drug-resistant microbe. This study aims to investigate the synergistic effects of PACT mediated by toluidine blue (TB), combined with gentamicin (GEN) on common pathogens Staphylococcus aureus (S. aureus) and multidrug-resistant S. aureus (MDR S. aureus).

METHODS

Alkaline lysis was used to detect the uptake of TB by S. aureus and MDR S. aureus. Plate counting was applied to evaluate the inhibition efficiency of GEN alone, TB-PACT alone, and work together. Flow cytometry and fluorescence microscopy were performed to examine the permeability of bacterial membranes after different treatments. Intracellular and extracellular reactive oxygen species (ROS) were assessed with the assist of H₂DCF-DA and SOSG probes.

RESULTS

TB-PACT combined with GEN led to more pronounced antibacterial effects in S. aureus and MDR S. aureus, as compared with either alone. TB-PACT treatment permeabilized the bacterial membranes, promoted GEN cellular accumulation and augmented the antibacterial efficiency. The intracellular ROS generation by the combination of TB-PACT and GEN was much higher than that of single treatment groups.

CONCLUSIONS

TB-PACT decreased the GEN cytotoxic threshold and usage, and the synergy of them significantly enhanced the sterilization of S. aureus and MDR S. aureus.

Photodynamic treatment for multidrug-resistant Gram-negative bacteria: Perspectives for the treatment of Klebsiella pneumoniae infections

The emergence of multi-drug resistance for pathogenic bacteria is one of the most pressing global threats to human health in the 21st century. Hence, the availability of new treatment becomes indispensable to prevent morbidity and mortality caused by infectious agents. This article reviews the antimicrobial properties of photodynamic therapy (PDT), which is based on the use of photosensitizers compounds (PSs). The PSs are non-toxic small molecules, which induce oxidative stress only under excitation with light. Then, the PDT has the advantage to be locally activated using phototherapy devices. We focus on PDT for the Klebsiella pneumoniae, as an example of Gram-negative bacteria, due to its relevance as an agent of health-associated infections (HAI) and a multi-drug resistant bacteria. K. pneumoniae is a fermentative bacillus, member of the Enterobacteriaceae family, which is most commonly associated with producing infection of the urinary tract (UTI) and pneumonia. K. pneumoniae infections may occur in deep organs such as bladder or lungs tissues; therefore, activating light must get access or penetrate tissues with sufficient power to produce effective PDT. Consequently, the rationale for selecting the most appropriate PSs, as well as photodynamic devices and photon fluence doses, were reviewed. Also, the mechanisms by which PDT activates the immune system and its importance to eradicate the infection successfully, are discussed.