Antimicrobial efficacy of methylene blue-mediated photodynamic therapy on titanium alloy surfaces in vitro

Antimicrobial Activity of Methylene Blue Associated with Photodynamic Therapy: In Vitro Study in Multi-Species Oral Biofilm

The control of infectious diseases caused by biofilms is a continuing challenge for researchers due to the complexity of their microbial structures and therapeutic implications. Photodynamic therapy as an adjunctive anti-infective treatment has been described as a possible valid approach but has not been tested in polymicrobial biofilm models. This study evaluated the effect of photodynamic therapy in vitro with methylene blue (MB) 0.01% and red LEDs (λ = 660 nm, power density ≈ 330 mW/cm2, 2 mm distance from culture) on the metabolic activity and composition of a multispecies subgingival biofilm. Test Groups LED and MB + LED showed a more significant reduction in metabolic activity than the non-LED application group (~50 and 55%, respectively). Groups LED and MB equally affected (more than 80%) the total bacterial count in biofilms. No differences were noted in the bacterial biofilm composition between the groups. In vitro LED alone or the MB + LED combination reduced the metabolic activity of bacteria in polymicrobial biofilms and the total subgingival biofilm count.

Type I photodynamic antimicrobial therapy: Principles, progress, and future perspectives

The emergence of drug-resistant bacteria has significantly diminished the efficacy of existing antibiotics in the treatment of bacterial infections. Consequently, the need for finding a strategy capable of effectively combating bacterial infections has become increasingly urgent. Photodynamic therapy (PDT) is considered one of the most promising emerging antibacterial strategies due to its non-invasiveness, low adverse effect, and the fact that it does not lead to the development of drug resistance. However, bacteria at the infection sites often exist in the form of biofilm instead of the planktonic form, resulting in a hypoxic microenvironment. This phenomenon compromises the treatment outcome of oxygen-dependent type-II PDT. Compared to type-II PDT, type-I PDT is not constrained by the oxygen concentration in the infected tissues. Therefore, in the treatment of bacterial infections, type-I PDT exhibits significant advantages over type-II PDT. In this review, we first introduce the fundamental principles of type-I PDT in details, including its physicochemical properties and how it generates reactive oxygen species (ROS). Next, we explore several specific antimicrobial mechanisms utilized by type-I PDT and summarize the recent applications of type-I PDT in antimicrobial treatment. Finally, the limitations and future development directions of type-I photosensitizers are discussed. STATEMENT OF SIGNIFICANCE: The misuse and overuse of antibiotics have accelerated the development of bacterial resistance. To achieve the effective eradication of resistant bacteria, pathfinders have devised various treatment strategies. Among these strategies, type I photodynamic therapy has garnered considerable attention owing to its non-oxygen dependence. The utilization of non-oxygen-dependent photodynamic therapy not only enables the effective elimination of drug-resistant bacteria but also facilitates the successful eradication of hypoxic biofilms, which exhibits promising prospects for treating biofilm-associated infections. Based on the current research status, we anticipate that the novel type I photodynamic therapy agent can surmount the biofilm barrier, enabling efficient treatment of hypoxic biofilm infections.

Effectiveness of mechanical and chemical decontamination methods for the treatment of dental implant surfaces affected by peri-implantitis: A systematic review and meta-analysis

OBJECTIVE

To assess which decontamination method(s) used for the debridement of titanium surfaces (disks and dental implants) contaminated with bacterial, most efficiently eliminate bacterial biofilms.

MATERIAL AND METHODS

A systematic search was conducted in four electronic databases between January 1, 2010 and October 31, 2022. The search strategy followed the PICOS format and included only in vitro studies completed on either dental implant or titanium disk samples. The assessed outcome variable consisted of the most effective method(s)-chemical or mechanical- removing bacterial biofilm from titanium surfaces. A meta-analysis was conducted, and data was summarized through single- and multi-level random effects model (p < .05).

RESULTS

The initial search resulted in 5260 articles after the removal of duplicates. After assessment by title, abstract, and full-text review, a total of 13 articles met the inclusion criteria for this review. Different decontamination methods were assessed, including both mechanical and chemical, with the most common method across studies being chlorhexidine (CHX). Significant heterogeneity was noted across the included studies. The meta-analyses only identified a significant difference in biofilm reduction when CHX treatment was compared against PBS. The remaining comparisons did not identify significant differences between the various decontamination methods.

CONCLUSIONS

The present results do not demonstrate that one method of decontamination is superior in eliminating bacterial biofilm from titanium disk and implant surfaces.

Comparative study of the effect of different exposure parameters of 635nm diode laser and toluidine blue O in eliminating Aggregatibacter actinomycetemcomitans biofilm from titanium implant surfaces

BACKGROUND

The aim of this study was to investigate the effects of antimicrobial photodynamic therapy (PDT) using 635 nm diode laser irradiation with an energy density of 6 to 30 J/cm2 and toluidine blue O (TBO) as a photosensitizer on the viability of Aggregatibacter actinomycetemcomitans attached to the surface of titanium implants.

MATERIALS AND METHODS

Titanium implants contaminated with A. actinomycetemcomitans were treated with TBO alone or in combination with different exposure parameters (light doses of 6 - 30 J/cm2 at 635 nm) and 0.2 % chlorhexidine (CHX). After treatment, colony forming units (CFUs)/ml were determined to assess PDT efficacy. The structure of the biofilm of A. actinomycetemcomitans was analyzed by field emission scanning electron microscopy (FESEM).

RESULTS

Under optimal conditions, the colony count was reduced by ∼90 %. Treatment with CHX was somewhat more effective (colony formation was reduced by ∼95 %), but this agent has adverse effects that can be avoided with PDT.

CONCLUSION

This study confirms the efficacy of PDT against A. actinomycetemcomitans depending on the light dose. Treatment with TBO + 635 nm diode laser has an effect that may be equivalent to that of CHX, but perhaps with fewer adverse effects.

In vitro cytotoxicity and antibacterial activity of hypochlorous acid antimicrobial agent

Background/purpose

Bacteria-associated oral diseases such as dental caries and periodontitis are widespread epidemics that cause oral pain and loss of function. The purpose of this study was to evaluate the in vitro cytotoxicity and antibacterial activity of different concentrations of hypochlorous acid (HOCl).

Materials and methods

Five different concentrations (100, 200, 300, 400, and 500 ppm) of HOCl were evaluated for their antimicrobial efficacy against Gram-negative (A. actinomycetcmcomitans and P. gingivalis) and Gram-positive bacteria (S. mutans and S. sanguinis) after treatment for 1 and 10 min. Sodium hypochlorite (NaOCl) and chlorhexidine (CHX) were used as positive controls. In addition, HOCl was examined for L929 cytotoxicity and RAW 264.7 growth.

Results

The bacteriostatic ratio of NaOCl was comparable to that of CHX and significantly (P < 0.05) higher than that of all HOCl solutions. Higher HOCl concentration had significantly (P < 0.05) higher antibacterial effect, and the bacteriostatic ratio of 10 min treatment was slightly higher than that of 1 min treatment. CHX and NaOCl seeded into L929 cells resulted in low cell viability with only 30-39%, much significantly (P < 0.05) lower than all HOCl groups (greater than 80%). All HOCl solutions met the recommendations of ISO 10993-5 and showed no cytotoxicity, although there was a concentration-dependent decrease in cell viability. All antimicrobial agents showed the same trend of response to RAW 264.7 as L929.

Conclusion

Within the limit of this study, 400 ppm HOCl disinfectant may be a potential antimicrobial candidate for mouthwash, endodontic irrigants, and periodontitis treatment.

The effect of photodynamic therapy in controlling the oral biofilm: A comprehensive overview

Several resistance mechanisms are involved in dental caries, including oral biofilms. An accumulation of bacteria on the surface of teeth is called plaque. Periodontitis and gingivitis are caused by dental plaque. In this review article, we aimed to review the studies associated with the application of photodynamic therapy (PDT) to prevent and treat various microbial biofilm-caused oral diseases in recent decades. There are several studies published in PubMed that have described antimicrobial photodynamic therapy (APDT) effects on microorganisms. Several in vitro and in vivo studies have demonstrated the potential of APDT for treating endodontic, periodontal, and mucosal infections caused by bacteria as biofilms. Reactive oxygen species (ROS) are activated in the presence of oxygen by integrating a nontoxic photosensitizer (PS) with appropriate wavelength visible light. By causing irreversible damage to microorganisms, ROS induces some biological and photochemical events. Testing several wavelengths has been conducted to identify potential PS for APDT. A standard protocol is not yet available, and the current review summarizes findings from dental studies on APDT.

Antimicrobial photodynamic therapy for the treatment of oral infections: A systematic review

Oral infection is a common clinical symptom. While antibiotics are widely employed as the primary treatment for oral diseases, the emergence of drug-resistant bacteria has necessitated the exploration of alternative therapeutic approaches. One such modality is antimicrobial photodynamic therapy (aPDT), which utilizes light and photosensitizers. Indeed, aPDT has been used alone or in combination with other treatment options dealing with periodontal disease for the elimination of biofilms from bacterial community to achieve bone formation and/or tissue regeneration. In this review article, in addition to factors affecting the efficacy of aPDT, various photosensitizers, the latest technology and perspectives on aPDT are discussed in detail. More importantly, the article emphasizes the novel design and clinical applications of photosensitizers, as well as the synergistic effects of chemical and biomolecules with aPDT to achieve the complete eradication of biofilms and even enhance the biological performance of tissues surrounding the treated oral area.

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

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

The role of the light source in antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (APDT) is a promising approach to fight the growing problem of antimicrobial resistance that threatens health care, food security and agriculture. APDT uses light to excite a light-activated chemical (photosensitiser), leading to the generation of reactive oxygen species (ROS). Many APDT studies confirm its efficacy in vitro and in vivo against bacteria, fungi, viruses and parasites. However, the development of the field is focused on exploring potential targets and developing new photosensitisers. The role of light, a crucial element for ROS production, has been neglected. What are the main parameters essential for effective photosensitiser activation? Does an optimal light radiant exposure exist? And finally, which light source is best? Many reports have described the promising antibacterial effects of APDT in vitro, however, its application in vivo, especially in clinical settings remains very limited. The restricted availability may partially be due to a lack of standard conditions or protocols, arising from the diversity of selected photosensitising agents (PS), variable testing conditions including light sources used for PS activation and methods of measuring anti-bacterial activity and their effectiveness in treating bacterial infections. We thus sought to systematically review and examine the evidence from existing studies on APDT associated with the light source used. We show how the reduction of pathogens depends on the light source applied, radiant exposure and irradiance of light used, and type of pathogen, and so critically appraise the current state of development of APDT and areas to be addressed in future studies. We anticipate that further standardisation of the experimental conditions will help the field advance, and suggest key optical and biological parameters that should be reported in all APDT studies. More in vivo and clinical studies are needed and are expected to be facilitated by advances in light sources, leading to APDT becoming a sustainable, alternative therapeutic option for bacterial and other microbial infections in the future.

Effective Biofilm Eradication on Orthopedic Implants with Methylene Blue Based Antimicrobial Photodynamic Therapy In Vitro

Periprosthetic joint infections (PJI) are difficult to treat due to biofilm formation on implant surfaces, often requiring removal or exchange of prostheses along with long-lasting antibiotic treatment. This in vitro study investigated the effect of methylene blue photodynamic therapy (MB-PDT) on PJI-causing biofilms on different implant materials. MB-PDT (664 nm LED, 15 J/cm²) was tested on different Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Cutibacterium acnes strains in both planktonic form and grown in early and mature biofilms on prosthetic materials (polyethylene, titanium alloys, cobalt-chrome-based alloys, and bone cement). The minimum bactericidal concentration with 100% killing (MBC_100%) was determined. Chemical and topographical alterations were investigated on the prosthesis surfaces after MB-PDT. Results showed a MBC_100% of 0.5-5 μg/mL for planktonic bacteria and 50-100 μg/mL for bacteria in biofilms-independent of the tested strain, the orthopedic material, or the maturity of the biofilm. Material testing showed no relevant surface modification. MB-PDT effectively eradicated common PJI pathogens on arthroplasty materials without damage to the materials, suggesting that MB-PDT could be used as a novel treatment method, replacing current, more invasive approaches and potentially shortening the antibiotic treatment in PJI. This would improve quality of life and reduce morbidity, mortality, and high health-care costs.

Photodynamic therapy and photobiomodulation therapy in zoledronic acid-induced osteonecrosis in rats

BACKGROUND

This study investigated the effect of antimicrobial photodynamic therapy (PDT), using methylene blue (MBO) and photobiomodulation therapy (PT), on the alveolar bone of rats submitted to bisphosphonate-induced osteonecrosis of the maxillaries (OMB) model using zoledronic acid (ZA).

METHODS

Sixty rats divided into six groups were used: SALINE, PDT, ZA, ZA+PDT, ZA+PT, and ZA+MBO. Three weekly administrations (Days 0, 7, and 14) of ZA 0.20 mg/kg or saline solution were performed. After one month (Day 42), the exodontia of the left lower first molars were performed. An additional dose of ZA was administered at Day 49. PDT was performed on days 42, 45, 49, and 54. One month after exodontia (Day 70), the animals were euthanized to obtain samples for imaging and microscopic analysis. ANOVA/Bonferroni tests were used for statistical analysis.

RESULTS

The ZA+PDT group showed a significantly lower percentage of apoptotic osteocytes than the ZA group (p<0.001). The ZA+MBO, ZA+PT, and PDT groups significantly reduced the number of mononuclear cells compared to the ZA group (p<0.001). The ZA+PT and ZA+PDT groups showed a significant reduction in the number of CD 68+ (p<0.001) and CD3+ (p=0.002) cells compared to the ZA group. The number of cells expressing INF-y had a significant reduction in the groups co-treated with PT and PDT compared to the ZA group (p<0.001).

CONCLUSIONS

We conclude that PDT and PT attenuated the severity of OMB and the inflammatory process due to a reduction of macrophages, T lymphocytes, and cytokines that stimulate the activity of these cells.

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

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

Methylene Blue-Based Nano and Microparticles: Fabrication and Applications in Photodynamic Therapy

Methylene blue (MB) has been used in the textile industry since it was first extracted by the German chemist Heinrich Caro. Its pharmacological properties have also been applied toward the treatment of certain diseases such as methemoglobinemia, ifosfamide-induced encephalopathy, and thyroid conditions requiring surgery. Recently, the utilization of MB as a safe photosensitizer in photodynamic therapy (PDT) has received attention. Recent findings demonstrate that photoactivated MB exhibits not only anticancer activity but also antibacterial activity both in vitro and in vivo. However, due to the hydrophilic nature of MB, it is difficult to create MB-embedded nano- or microparticles capable of increasing the clinical efficacy of the PDT. This review aims to summarize fabrication techniques for MB-embedded nano and microparticles and to provide both in vitro and in vivo examples of MB-mediated PDT, thereby offering a future perspective on improving this promising clinical treatment modality. We also address examples of MB-mediated PDT in both cancer and infection treatments. Both in-vitro and in-vivo studies are summarized here to document recent trends in utilizing MB as an effective photosensitizer in PDT. Lastly, we discuss how developing efficient MB-carrying nano- and microparticle platforms would be able to increase the benefits of PDT.

Microbial Biofilm Decontamination on Dental Implant Surfaces: A Mini Review

Introduction

After insertion into the bone, implants osseointegrate, which is required for their long-term success. However, inflammation and infection around the implants may lead to implant failure leading to peri-implantitis and loss of supporting bone, which may eventually lead to failure of implant. Surface chemistry of the implant and lack of cleanliness on the part of the patient are related to peri-implantitis. The only way to get rid of this infection is decontamination of dental implants.

Objective

This systematic review intended to study decontamination of microbial biofilm methods on titanium implant surfaces used in dentistry.

Methods

The electronic databases Springer Link, Science Direct, and PubMed were explored from their inception until December 2020 to identify relevant studies. Studies included had to evaluate the efficiency of new strategies either to prevent formation of biofilm or to treat matured biofilm on dental implant surfaces.

Results and Discussion

In this systematic review, 17 different groups of decontamination methods were summarized from 116 studies. The decontamination methods included coating materials, mechanical cleaning, laser treatment, photodynamic therapy, air polishing, anodizing treatment, radiation, sonication, thermal treatment, ultrasound treatment, chemical treatment, electrochemical treatment, antimicrobial drugs, argon treatment, and probiotics.

Conclusion

The findings suggest that most of the decontamination methods were effective in preventing the formation of biofilm and in decontaminating established biofilm on dental implants. This narrative review provides a summary of methods for future research in the development of new dental implants and decontamination techniques.

Optical profile: A key determinant of antibacterial efficacy of photodynamic therapy in dentistry

BACKGROUND

Periodontal disease effects 20-50% of the population worldwide, posing a global health challenge. It has been reported to be more prevalent among adults. Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) is an important organism associated with localized juvenile periodontitis. Photodynamic therapy (PDT) has been widely utilized for the treatment of periodontal disease; however, the effect of laser (light) profile on the antibacterial efficacy of PDT remains to be established. The quantitative measurement of laser profile is required to confirm the in vitro efficacy of PDT.

AIM

In the present study, a low cost PDT system comprising of six copper tube waveguides (CTW) was developed to provide more uniform irradiation of the culture plate.

METHODS

The antibacterial effect of PDT, in combination with 200 μg/mL methylene blue (MB) as photosensitizer and 60 sec of irradiation, was studied on A. actinomycetemcomitans and Streptococcus mutans (S. mutans). In the present case, 660 nm laser guided with unpolished CTW, polished CTW, and optical fiber waveguide (OFW) provided radiant exposure of 0.86, 1.38, and 1.36 J/cm², respectively, for a 24-well culture plate.

RESULTS

The designed PDT system provided antimicrobial efficacy of 98% and 91% for A. actinomycetemcomitans and S. mutans, respectively, which was significantly higher as compared to OFW guided PDT.

CONCLUSION

The results of the study highlighted the importance of laser profile as a key parameter that determines the survival rate of bacteria at the edge of the culture plate. Thus, the dose of PDT at the margin of optical profile is important for antibacterial activity for in vitro evaluation.

Synergistic Photoantimicrobial Chemotherapy of Methylene Blue-Encapsulated Chitosan on Biofilm-Contaminated Titanium

Intensive efforts have been made to eliminate or substantial reduce bacterial adhesion and biofilm formation on titanium implants. However, in the management of peri-implantitis, the methylene blue (MB) photosensitizer commonly used in photoantimicrobial chemotherapy (PACT) is limited to a low retention on the implant surface. The purpose of this study was to assess enhancive effect of water-soluble quaternary ammonium chitosan (QTS) on MB retention on biofilm-infected SLA (sandblasted, large grid, and acid-etched) Ti alloy surfaces in vitro. The effectiveness of QTS + MB with different concentrations in eliminating Gram-negative A. actinomycetemcomitans or Gram-positive S. mutans bacteria was compared before and after PACT. Bacterial counting and lipopolysaccharide (LPS) detection were examined, and then the growth of human osteoblast-like MG63 cells was evaluated. The results indicated that the synergistic QTS + MB with retention ability significantly decreased the biofilm accumulation on the Ti alloy surface, which was better than the same concentration of 1 wt% methyl cellulose (MC). More importantly, the osteogenic activity of MG63 cells on the disinfected sample treated by QTS + MB-PACT modality was comparable to that of sterile Ti control, significantly higher than that by MC + MB-PACT modality. It is concluded that, in terms of improved retention efficacy, effective bacteria eradication, and enhanced cell growth, synergistically, PACT using the 100 μg/mL MB-encapsulated 1% QTS was a promising modality for the treatment of peri-implantitis.

Electrosprayed calcium silicate nanoparticle-coated titanium implant with improved antibacterial activity and osteogenesis

To ensure clinical success, the implant and the surrounding bone tissue must not only be integrated, but also must not be suspected of infection. In this work, an antibacterial and bioactive nanostructured calcium silicate (CaSi) layer on titanium substrate by an electrospray deposition method was prepared, followed by annealing at 700, 750 and 800 °C to improve the bonding strength of the CaSi coating. The phase composition, microstructure and bonding strength of the CaSi coatings were examined. Human mesenchymal stem cells (hMSCs), Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) species were used to analyze the osteogenic and antibacterial activity of the coatings, respectively. Experimental results showed that the as-prepared CaSi coating was mainly composted of β-dicalcium silicate phase with a particle size of about 300 nm. After annealing, the thickness of the oxidation reaction layer increased obviously from 0.3 μm to 1 μm with increase in temperature, which was confirmed by the cross-sectional morphology and element depth profile. The bonding strength of the coating annealed at 750 °C (19.0 MPa) was significantly higher (p < 0.05) than that of the as-prepared coating (4.4 MPa) and the ISO 13,779 standard (15 MPa). The results of antibacterial efficacy and stem cell osteogenesis consistently elaborated that the 750 °C-annealed coating had higher activity than the as-prepared coating and the Ti control. It is concluded that after annealing at 750 °C, the CaSi nanoparticle-coated Ti implant had good bond strength, osteogenic and antibacterial activity.

Effect of long-term methylene blue treatment on the composition of mouse gut microbiome and its relationship with the cognitive abilities of mice

In recent years, methylene blue (MB) has attracted considerable interest as a potential drug for the treatment of methemoglobinemia and neurodegenerative diseases. MB is active against microorganisms from various taxonomic groups. However, no studies have yet been conducted on the effect of MB on the intestinal microbiome of model animals. The aim of this work was to study the effect of different concentrations of MB on the mouse gut microbiome and its relationship with the cognitive abilities of mice. We showed that a low MB concentration (15 mg/kg/day) did not cause significant changes in the microbiome composition. The Bacteroidetes/Firmicutes ratio decreased relative to the control on the 2nd and 3rd weeks. A slight decrease in the levels Actinobacteria was detected on the 3rd week of the experiment. Changes in the content of Delta, Gamma, and Epsilonproteobacteria have been also observed. We did not find significant alterations in the composition of intestinal microbiome, which could be an indication of the development of dysbiosis or other gut dysfunction. At the same time, a high concentration of MB (50 mg/kg/day) led to pronounced changes, primarily an increase in the levels of Delta, Gamma and Epsilonproteobacteria. Over 4 weeks of therapy, the treatment with high MB concentration has led to an increase in the median content of Proteobacteria to 7.49% vs. 1.61% in the control group. Finally, we found that MB at a concentration of 15 mg/kg/day improved the cognitive abilities of mice, while negative correlation between the content of Deferribacteres and cognitive parameters was revealed. Our data expand the understanding of the relationship between MB, cognitive abilities, and gut microbiome in respect to the antibacterial properties of MB.

Photosensitizers attenuate LPS-induced inflammation: implications in dentistry and general health

Antimicrobial photodynamic therapy (aPDT) is a complementary therapeutic modality for periodontal and endodontic diseases, in which Gram-negative bacteria are directly involved. Currently, there are few evidences regarding the effects of aPDT on bacterial components such as lipopolysaccharide (LPS) and it would represent a major step forward in the clinical use of this therapy. In this context, this study aimed to evaluate the efficacy of different photosensitizers (PSs) used in aPDT in LPS inhibition. Four PSs were used in this study: methylene blue (MB), toluidine blue (TBO), new methylene blue (NMB), and curcumin (CUR). Different approaches to evaluate LPS interaction with PSs were used, such as spectrophotometry, Limulus amebocyte lysate (LAL) test, functional assays using mouse macrophages, and an in vivo model of LPS injection. Spectrophotometry showed that LPS decreased the absorbance of all PSs used, indicating interactions between the two species. LAL assay revealed significant differences in LPS concentrations upon pre-incubation with the different PSs. Interestingly, the inflammatory potential of LPS decreased after previous treatment with the four PSs, resulting in decreased secretion of inflammatory cytokines by macrophages. In vivo, pre-incubating curcumin with LPS prevented animals from undergoing septic shock within the established time. Using relevant models to study the inflammatory activity of LPS, we found that all PSs used in this work decreased LPS-induced inflammation, with a more striking effect observed for NMB and curcumin. These data advance the understanding of the mechanisms of LPS inhibition by PSs.

Effect of rutin as flavonoid compound on photodynamic inactivation against P. aeruginosa and S. aureus

Antimicrobial photodynamic therapy (aPDT) has drawn increasing attention for its potential to effectively kill multidrug-resistant pathogenic bacteria and also for its low tendency to induce drug resistance. Antimicrobial photodynamic therapy (aPDT) is the application of photoactive dye followed by light irradiation that leads to the death of microbial cells mainly by reactive oxygen species (ROS) production in the presence of oxygen molecules. Methylene Blue (MB) as a photosensitizer is a hydrophobic drug molecule and prone to aggregation and dimer formation which lead to its low phototoxicity. Rutin, a flavonoid compound which is derived from plants such as wheat, apple, and tea has many properties such as antibacterial activity. In this study, we investigated the effect of rutin as a flavonoid compound on photodynamic inactivation by MB on Pseudomonas aeruginosa and Staphylococcus aureus. After performing the Minimum Inhibitory Concentration (MIC) assay (to measure minimum inhibitory concentration) and the MTT assay (to evaluate methylene blue toxicity), the effect of aPDT at 660 nm and pretreatment or post treatment with rutin on bacteria in the forms of planktonic and biofilm were investigated. The results showed that by a combination of rutin (800 μg/mL) with methylene blue (MB 8 μg/mL) as a photosensitizer and aPDT (660 nm, 5 min), there is a more reduction in the number of bacteria in the planktonic condition and bacterial biofilm production in comparison to MB alone. MB-aPDT showed no toxic effect against human dermal fibroblast with the proposed strategy which could suggest its application with rutin as a novel approach in the treatment of bacteria in wound infection.

Assessment of safety and efficacy of antimicrobial photodynamic therapy for peri-implant disease

BACKGROUND

There is no reliable treatment procedure for peri-implant disease, despite the rise in its incidence. This study sought to evaluate the short-term safety and efficacy of antimicrobial photodynamic therapy (a-PDT) on peri-implantitis by assessing the volume of pus discharge after a-PDT.

METHODS

Patients with pus discharge from a peri-implant pocket were recruited from December 1st, 2019 to April 30th, 2020. The enrolled implants were randomly assigned to one of two groups, the irrigation and a-PDT groups. Their peri-implant pocket was irrigated with normal saline in the irrigation group, and a saline irrigation and subsequent a-PDT with toluidine blue (TB) was performed in the a-PDT group. The safety and efficacy of a-PDT were assessed 7 days after treatment.

RESULTS

Twenty-five implants in 21 patients (irrigation group; 13 implants, a-PDT group; 12 implants) were registered. No complication was observed after a-PDT. Pus discharge was decreased in 7 of 12 implants (58.3 %) in the a-PDT group, and in 2 of 13 implants (15.4 %) in the irrigation group. According to Fisher's exact test, a-PDT resulted in a statistically significant decrease in pus discharge compared to irrigation alone (p = 0.0414).

CONCLUSIONS

a-PDT was confirmed to be a safe treatment for peri-implantitis, and the short-term efficacy of a-PDT with TB on peri-implantitis was clarified. Nevertheless, its efficacy remains restricted, and a new combination therapy of a-PDT and decontamination procedures is expected to be developed in future.

Antimicrobial photodynamic therapy associated with bone regeneration for peri-implantitis treatment: A case report

Antimicrobial photodynamic therapy (aPDT) has emerged as a promising alternative to promote bacterial elimination and crestal bone remodeling in patients affected by peri-implantitis, once it is able to access the implant microstructure at the most restricted sites with no damage to implant surface. This paper reports a 6-month follow-up of a patient with peri-implantitis treated by surgical approach with adjunct photodynamic therapy associated to guided bone regeneration. A full thickness open-flap was performed to allow directly mechanical debridement, followed by aPDT using methylene blue 200 μg/mL under red laser irradiation (660 nm, 100 mW, 9 J), providing decontamination of implant surface and surrounding tissue. Photosensitizer was washed twice with saline solution previously to guided bone regeneration, which was carried out using xenogeneic bone and resorbable collagen membrane. After 6-month follow-up, the use of aPDT as an adjunct therapy to the surgical treatment of peri-implantitis promoted sufficient decontamination, clear evidence of bone regeneration, and peri-implant health restoration.

Comparison of photodynamic therapy with methylene blue associated with ceftriaxone in gram-negative bacteria; an in vitro study

The resistance of microorganisms increases the need for new antimicrobial therapies. The aim of this study was to evaluate the in vitro action of photodynamic therapy and its combination with ceftriaxone in third generation cephalosporin resistant gram-negative bacteria. Clinical strains of Klebsiella pneumoniae, Enterobacter aerogenes and Escherichia coli were obtained, incubated with MB for 15 min combined or not with ceftriaxone and irradiated with fluence of 10 and 25 J/cm². MB internalization was evaluated by confocal microscopy. Cell viability was assessed by counting colony forming units and bacterian metabolism by the resazurin test. MB has been observed within cells, although not in all bacteria. PDT-MB alone and combined with Ceftriaxone reduced bacterial growth by approximately 1 log at 10 J/cm² of fluence and 4 logs by 25 J/cm², with a significant difference from the control group. The reduction in bacterial growth between the treated groups was similar, without significant difference between them. The Resazurin test showed lower bacterial metabolic activity in the treated groups, but it did not allow to observe difference between fluences. It was concluded with this study that the internalization of MB was not observed in all cells of K. pneumoniae, E. aerogenes and E. coli strains. There was less bacterial metabolic activity in the treated groups, with no variation between different fluences. PDT-MB 25 J/cm² alone and combined with Ceftriaxone showed antimicrobial action, but the PDT-MB/Ceftriaxone combination had no potentiating effect.

Carbohydrate coated fluorescent mesoporous silica particles for bacterial imaging

This work investigated the synthesis of carbohydrate functionalized methylene blue doped amine grafted mesoporous silica nanoparticles (MB AMSN) and their application in bioimaging. A single-pot synthesis methodology was developed via a modified co-condensation sol-gel technique for simultaneous incorporation of the dye molecule in the nanoparticles, with amine grafting for subsequent functionalization. The obtained nanoparticles (∼ 450 nm) are mesoporous and have a high surface area (538 m²/g), pore-volume (0.3 cm³/g), showed excellent UV-vis absorbance, and dye encapsulation efficiency (> 75 %). These fluorescent nanoparticles were further functionalized with carbohydrate molecules before application as contrast agents in bacterial cells. In the present study, gram-positive (E. coli) and gram-negative (B. subtilis) bacteria were used as model organisms. Confocal laser microscopy results showed that the nanoparticles are highly fluorescent, and SEM of glucose conjugated MB doped nanoparticles indicated close interaction with E. coli with no toxicity observed towards either bacterial cells. The results demonstrate that by suitable surface functionalization, the methylene blue doped silica nanoparticles can be used as bioimaging agents.

Oral microbiological control by photodynamic action in orthodontic patients

BACKGROUND

Orthodontics involves diagnosis and treatment of dental and skeletal malocclusions. Orthodontic apparatus may repair these malocclusions but may also impair oral hygiene making patients prone to develop both periodontal diseases and caries. Antimicrobial agents may be used to prevent this.To avoid increased antimicrobial resistance to available drugs, A-PDT (Antimicrobial Photodynamic Therapy) appears as a viable alternative.

OBJECTIVE

This work aimed to evaluate the efficacy of A-PDT on reducing the number of colony forming units (CFU) through the use of phenothiazine compound (methylene blue+ toluidine blue) as a photosensitizer, associated with red LED (λ640±5ηm) irradiation in orthodontic patients.

METHODOLOGY

Twenty-one patients consented to participate in the study. Three biofilm collections were performed around the brackets and gums of the inferior central incisors; first before any intervention (Control); second after 5min of pre-irradiation and the last one immediately after AmPDT. Subsequently, a microbiological routine for microorganism growth period were performed and CFU counting after a 24h done.

RESULTS

The data showed that the AmPDT was able to reduce CFU count around 90% when compared to Control group (p=0.007) and also between the A-PDT and Photosensitizer groups (p=0.010). However, there were no differences between the Control and Photosensitizer groups.

CONCLUSION

A-PDT associated with the use of phenothiazine compounds and red LED was able to significantly reduce the number of CFUs in orthodontic patients.

In vitro Assessment of Peri-implantitis Treatment Procedures: A Review

Background:

The prevalence of peri-implantitis is increasing continuously and such a biological complication significantly decreases implant survival and success. Although various treatment modalities have been identified for peri-implantitis, no completely efficient method has yet been established.

Objective:

The aim of this review was to evaluate the scientific literature regarding the in vitro effects of peri-implantitis treatment.

Methods:

A review of the literature was performed by using Google Scholar, PubMed/ MEDLINE and Science Direct databases. In vitro studies on peri-implantitis treatment modalities were selected. The search strategy identified 57 eligible studies. After selection, 21 articles met all the inclusion criteria and were included in the present review.

Results:

Included in vitro studies evaluated different types of peri-implantitis treatment modalities such as mechanical, chemical, combination and laser therapies. Combination therapies with the aid of adjuvants were found to be more effective compared to the studies that used only one type of treatment modality. Laser systems were also tested and displayed interesting results in terms of surface decontamination with a variability associated with selected parameters.

Conclusion:

This review was performed to evaluate the efficacy of the treatment modalities used for peri-implantitis in vitro. Although there are various effective treatment methods, none has been completely successful in removing the biofilms related to peri-implantitis. The findings imply the need for further studies to develop more effective antimicrobial treatment procedures.

Enhancing osteoblast functions on biofilm-contaminated titanium alloy by concentration-dependent use of methylene blue-mediated antimicrobial photodynamic therapy

The concentration of methylene blue (MB) photosensitizer could affect the eradication efficacy of antimicrobial photodynamic therapy (aPDT) in the treatment of contaminated implants, which is linked to the osseointegration of the implant. We evaluated osteoblast functions on the contaminated SLA (sandblasting, large-grit and acid-etching) Ti alloy surfaces after the concentration-dependent use of MB-aPDT. Totally 1164 SLA discs were randomly distributed for the analyses of antibacterial efficacy and osteoblast functions. Gram-negative (Aggregatibacter actinomycetemcomitans; A. actinomycetemcomitans) or Gram-positive (Streptococcus mutans; S. mutans) adhered on disc samples was subjected to aPDT with different MB concentrations (200, 250, 300, 350, and 400 μg/mL) using 660 nm diode laser with maximum output 80 mW for 1 min irradiation (4.8 J/cm²). Bactericidal effect was examined by viability, morphology, and lipopolysaccharide (LPS) assays. The disinfected disc surfaces by MB-aPDT to support osteoblast-like MG63 attachment, proliferation, differentiation, and mineralization were assessed for the predetermined culture time intervals. The statistical differences between the means were performed using a one-way analysis of variance (ANOVA) with a post hoc Scheffe test. The results of the morphology observation and bacterial survival examination consistently indicated a remarkably lower quantity of bacterial colonies on biofilm-contaminated surfaces after the aPDT treatment with higher MB concentration. Similarly, the higher MB concentration in aPDT resulted in the lower LPS amounts remaining on the A. actinomycetemcomitans-contaminated surfaces. Intriguingly, the expression of osteoblast cultured on disinfected surfaces using aPDT with higher MB concentration was comparable to the control without contamination. Within the limits of this in vitro model, this formulation of 400 μg/mL MB used in aPDT may be not only the lethal concentration against the 2 bacteria-contaminated implants, but it could also enhance the osteoblast functions on the contaminated implants. Nevertheless, the efficacy in the clinical practice for peri-implantitis therapy remains to be studied.

Evaluation of physicochemical properties and bacterial photoinactivation of phenothiazine photosensitizers

We report herein the physicochemical properties and antimicrobial activity of a new monobrominated derivative of Azure B and its parent compound.

A maltoheptaose-decorated BODIPY photosensitizer for photodynamic inactivation of Gram-positive bacteria

A maltoheptaose-decorated BODIPY with high singlet oxygen generation efficacy was synthesized for photodynamic inactivation of Gram-positive bacteria in planktonic forms and biofilms.