Antibiofilm action of a toluidine blue O-silver nanoparticle conjugate on Streptococcus mutans: a mechanism of type I photodynamic therapy

Nanomaterial-based drug-delivery system as an aid to antimicrobial photodynamic therapy in treating oral biofilm

Diverse microorganisms live as biofilm in the mouth accounts for oral diseases and treatment failure. For decades, the prevention and treatment of oral biofilm is a global challenge. Antimicrobial photodynamic therapy (aPDT) holds promise for oral biofilm elimination due to its several traits, including broad-spectrum antimicrobial capacity, lower possibility of resistance and low cytotoxicity. However, the physicochemical properties of photosensitizers and the biological barrier of oral biofilm have limited the efficiency of aPDT. Nanomaterials has been used to fabricate nanocarriers to improve photosensitizer properties and thus enhance antimicrobial effect. In this review, we have discussed the challenges of aPDT used in dentistry, categorized the nanomaterial-delivery system and listed the possible mechanisms involved in nanomaterials when enhancing aPDT effect.

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.

The Facile Synthesis of Eco-Friendly Zinc Magnesium Bimetal Nanoparticles and its Application in the Eradication of Xanthomonas oryzae pv. oryzae that Causes Leaf Blight Disease of Rice

In this research work, we formulated and successfully assessed the antibacterial capability of zinc magnesium bimetal nanoparticles (ZnMgNPs) against Xanthomonas oryzae pv. oryzae (Xoo), the pathogenic microorganism responsible for causing the destructive leaf blight disease in rice. Successful preparation of ZnMgNPs were determined by UV-vis spectroscopy, EDX (Energy dispersive X-ray), FTIR (Fourier transform infrared) and SEM (Scanning Electron Microscopy). ZnMgNPs had antibacterial efficacy towards Xoo at MIC (minimum inhibitory concentration) 50 µg/ml. ZnMgNPs impeded the formation of biofilm of Xoo by drastically reducing the amount of EPS (extracellular polymeric substances) production and number of sessile cells. The ZnMgNPs also reduced several pathogenic traits of Xoo like motility, xanthomonadin and exoenzymes production. ZnMgNPs target cell membrane of Xoo and also induced oxidative damage as mechanisms of its antibacterial activity. As revealed by an ex-vivo study, ZnMgNPs diminished BLB (bacterial leaf blight) disease symptoms in rice leaves, ZnMgNPs had no effect on rice seed germination, and that following foliar application, the length and biomass of roots and shoots of rice seedling were unaffected, low cytotoxic to A549 cell line showing that ZnMgNPs are non-toxic. However, with ZnMgNPs treatment, the chlorophyll content index (CCI) increased significantly, indicating a good impact on rice physiology. All of these findings suggest that ZnMgNPs could be applied in agriculture to combat the Xoo-caused BLB disease.

Antimicrobial Activity of Selenium Nanoparticles (SeNPs) against Potentially Pathogenic Oral Microorganisms: A Scoping Review

Biofilms are responsible for the most prevalent oral infections such as caries, periodontal disease, and pulp and periapical lesions, which affect the quality of life of people. Antibiotics have been widely used to treat these conditions as therapeutic and prophylactic compounds. However, due to the emergence of microbial resistance to antibiotics, there is an urgent need to develop and evaluate new antimicrobial agents. This scoping review offers an extensive and detailed synthesis of the potential role of selenium nanoparticles (SeNPs) in combating oral pathogens responsible for causing infectious diseases. A systematic search was conducted up until May 2022, encompassing the MEDLINE, Embase, Scopus, and Lilacs databases. We included studies focused on evaluating the antimicrobial efficacy of SeNPs on planktonic and biofilm forms and their side effects in in vitro studies. The selection process and data extraction were carried out by two researchers independently. A qualitative synthesis of the results was performed. A total of twenty-two articles were considered eligible for this scoping review. Most of the studies reported relevant antimicrobial efficacy against C. albicans, S. mutans, E. faecalis, and P. gingivalis, as well as effective antioxidant activity and limited toxicity. Further research is mandatory to critically assess the effectiveness of this alternative treatment in ex vivo and in vivo settings, with detailed information about SeNPs concentrations employed, their physicochemical properties, and the experimental conditions to provide enough evidence to address the construction and development of well-designed and safe protocols.

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

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

Untargeted Metabolomics for Unraveling the Metabolic Changes in Planktonic and Sessile Cells of Salmonella Enteritidis ATCC 13076 after Treatment with Lippia origanoides Essential Oil

Nontyphoidal Salmonella species are one of the main bacterial causes of foodborne diseases, causing a public health problem. In addition, the ability to form biofilms, multiresistance to traditional drugs, and the absence of effective therapies against these microorganisms are some of the principal reasons for the increase in bacterial diseases. In this study, the anti-biofilm activity of twenty essential oils (EOs) on Salmonella enterica serovar Enteritidis ATCC 13076 was evaluated, as well as the metabolic changes caused by Lippia origanoides thymol chemotype EO (LOT-II) on planktonic and sessile cells. The anti-biofilm effect was evaluated by the crystal violet staining method, and cell viability was evaluated through the XTT method. The effect of EOs was observed by scanning electron microscopy (SEM) analysis. Untargeted metabolomics analyses were conducted to determine the effect of LOT-II EO on the cellular metabolome. LOT-II EO inhibited S. Enteritidis biofilm formation by more than 60%, without decreasing metabolic activity. Metabolic profile analysis identified changes in the modulation of metabolites in planktonic and sessile cells after LOT-II EO treatment. These changes showed alterations in different metabolic pathways, mainly in central carbon metabolism and nucleotide and amino acid metabolism. Finally, the possible mechanism of action of L. origanoides EO is proposed based on a metabolomics approach. Further studies are required to advance at the molecular level on the cellular targets affected by EOs, which are promising natural products for developing new therapeutic agents against Salmonella sp. strains.

Photodynamic antimicrobial therapy (AmPDT) using 1,9-Dimethyl-Methylene Blue zinc chloride double salt - DMMB and λ640 ± 5ηm LED light in patients undertaking orthodontic treatment

Orthodontic treatment involves the use of apparatuses that impairs oral hygiene making patients susceptible to periodontal diseases and caries. To prevent increased antimicrobial resistance AmPDT has shown itself a feasible option. The aim of this investigation was to assess the efficiency of AmPDT employing 1,9-Dimethyl-Methylene Blue zinc chloride double salt - DMMB as a photosensitizing agent combined with red LED irradiation (λ640 ± 5 ηm) against oral biofilm of patients undertaking orthodontic treatment. Twenty-one patients agreed to participate. Four biofilm collections were carried out on brackets and gingiva around inferior central incisors; first was carried out before any treatment (Control); second followed five minutes of pre-irradiation, the third was immediately after the first AmPDT, and the last after a second AmPDT. Then, a microbiological routine for microorganism growth was carried out and, after 24-h, CFU counting was performed. There was significant difference between all groups. No significant difference was seen between Control and Photosensitizer and AmpDT1 and AmPDT2 groups. Significant differences were observed between Control and AmPDT1 and AmPDT2 groups, Photosensitizer and AmPDT1 and AmPDT2 groups. It was concluded that double AmPDT using DMBB in nano concentration and red LED was capable to meaningfully decrease the number of CFUs in orthodontic patients.

Clinical applications of antimicrobial photodynamic therapy in dentistry

Given the emergence of resistant bacterial strains and novel microorganisms that globally threaten human life, moving toward new treatment modalities for microbial infections has become a priority more than ever. Antimicrobial photodynamic therapy (aPDT) has been introduced as a promising and non-invasive local and adjuvant treatment in several oral infectious diseases. Its efficacy for elimination of bacterial, fungal, and viral infections and key pathogens such as Streptococcus mutans, Porphyromonas gingivalis, Candida albicans, and Enterococcus faecalis have been investigated by many invitro and clinical studies. Researchers have also investigated methods of increasing the efficacy of such treatment modalities by amazing developments in the production of natural, nano based, and targeted photosensitizers. As clinical studies have an important role in paving the way towards evidence-based applications in oral infection treatment by this method, the current review aimed to provide an overall view of potential clinical applications in this field and summarize the data of available randomized controlled clinical studies conducted on the applications of aPDT in dentistry and investigate its future horizons in the dental practice. Four databases including PubMed (Medline), Web of Science, Scopus and Embase were searched up to September 2022 to retrieve related clinical studies. There are several clinical studies reporting aPDT as an effective adjunctive treatment modality capable of reducing pathogenic bacterial loads in periodontal and peri-implant, and persistent endodontic infections. Clinical evidence also reveals a therapeutic potential for aPDT in prevention and reduction of cariogenic organisms and treatment of infections with fungal or viral origins, however, the number of randomized clinical studies in these groups are much less. Altogether, various photosensitizers have been used and it is still not possible to recommend specific irradiation parameters due to heterogenicity among studies. Reaching effective clinical protocols and parameters of this treatment is difficult and requires further high quality randomized controlled trials focusing on specific PS and irradiation parameters that have shown to have clinical efficacy and are able to reduce pathogenic bacterial loads with sufficient follow-up periods.

Does potassium iodide help in the microbial reduction of oral microcosm biofilms after photodynamic therapy with methylene blue and red laser?

OBJECTIVE

To evaluate the efficacy of methylene blue (MB)-mediated antimicrobial photodynamic therapy (aPDT) doped with potassium iodide (KI) against oral microcosms biofilms cultured in dentin.

METHODS

A saliva-glycerol stock formed from pooled human saliva was diluted in McBain artificial saliva with 1% sucrose (1:1), inoculated on bovine dentin blocks, and refreshed daily for 5 days. The biofilms were divided (n = 9/group) and treated with 0.9% NaCl (C), 0.2% chlorhexidine (CX), 0.01% MB + low-power laser 15 J, 88 mW, 180 s (PL), and 0.01% MB + 50 mM KI + laser (PKIL). Serial dilution was performed, and cellular viability (CFU/mL) was evaluated for total microorganisms, total lactobacilli, total streptococci, and S. mutans. Additional biofilms were cultured and treated (n = 4) for biomass determination (%BMR). The microscopic structure of the biofilms was observed by SEM. One-way ANOVA and Tukey tests were conducted (α=5%).

RESULTS

Total microorganisms and total streptococci significantly reduced in biofilms treated with CX and PKIL when compared to C, but the CX, PKIL, and PL treatments did not differ from each other. Total lactobacilli and S. mutans showed a significant reduction in the CX, PL, and PKIL groups when compared to C, but with no difference between them. Biomass analysis showed a significantly reduction for CX and PKIL compared to C. SEM micrographs showed noticeable changes in bacterial membrane integrity for the PKIL and CX groups.

CONCLUSION

The addition of KI to methylene blue-mediated aPDT in microcosm biofilms was effective in reducing oral microorganisms, but the effect was group dependent.

Photodynamic antibacterial and antibiofilm activity of riboflavin against Xanthomonas oryzae pv oryzae: an ecofriendly strategy to combat bacterial leaf blight (BLB) rice disease

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv oryzae (Xoo), is one of the most damaging rice diseases, causing severe production losses depending on the rice variety. The purpose of this study was to develop an antibacterial photodynamic treatment (aPDT) using riboflavin for the treatment of BLB disease. Combining light and riboflavin (RF) therapy significantly reduced bacterial planktonic cells compared to RF alone. Photoactivated riboflavin also decreased biofilm biomass by reducing the number of viable sessile cells and the production of extracellular polymeric substances (EPS). Reactive oxygen species (ROS) levels in Xoo cells treated with photoactivated riboflavin were found to be significantly higher than in cells treated with riboflavin and light individually. Malondialdehyde (MDA) increased greatly in photoactivated riboflavin treated cells, indicating that severe oxidative damage was induced. Subsequently, a reduction in lactate dehydrogenase (LDH) activity in photoactivated riboflavin treated Xoo cells indicates that oxidative stress has disrupted the respiratory system, leading to bacterial cell death. In an ex vivo aPDT assay, photoactivated riboflavin successfully eradicated Xoo on the surface of rice leaves. Photoactivated riboflavin had no side effects on rice seed germination in subsequent trials, indicating that it is safe for agricultural applications. Therefore, all these findings suggest that aPDT is a potential alternative management strategy for BLB disease.

The Potential Application of Natural Photosensitizers Used in Antimicrobial Photodynamic Therapy against Oral Infections

Oral health problems and the emergence of antimicrobial resistance among pathogenic bacterial strains have become major global challenges and are essential elements that negatively affect general well-being. Antimicrobial photodynamic therapy (APDT) is based on a light source and oxygen that activates a nontoxic photosensitizer, resulting in microbial destruction. Synthetic and natural products can be used to help the APDT against oral microorganisms. The undesirable consequences of conventional photosensitizers, including toxicity, and cost encourage researchers to explore new promising photosensitizers based on natural compounds such as curcumin, chlorella, chlorophyllin, phycocyanin, 5-aminolevulinic acid, and riboflavin. In this review, we summarize in vitro studies describing the potential use of APDT therapy conjugated with some natural products against selected microorganisms that are considered to be responsible for oral infections.

Nanomaterials enabling clinical translation of antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (aPDT) has emerged as a promising approach to aid the fight against looming antibiotic resistance. aPDT harnesses the energy of light through photosenstizers to generate highly reactive oxygen species that can inactivate bacteria and fungi with no resistance. To date aPDT has shown great efficacy against microbes causing localized infections in the skin and the oral cavity. However, its wide application in clinical settings has been limited due to both physicochemical and biological challenges. Over the past decade nanomaterials have contributed to promoting photosensitizer performance and aPDT efficiency, yet further developments are required to establish accredited treatment options. In this review we discuss the challenges facing the clinical application of aPDT and the opportunities that nanotechnology may offer to promote the safety and efficiency of aPDT.

The application of selenium nanoparticles for enhancing the efficacy of photodynamic inactivation of planktonic communities and the biofilm of Streptococcus mutans

Objective

Streptococcus mutans is one of the principal causative agents of dental caries (tooth decay) found in the oral cavity. Therefore, this study investigates whether selenium nanoparticles (SeNPs) enhance the efficacy of photodynamic therapy (PDT) against both planktonic communities and the one-day-old biofilm of S. mutans. In this study, the planktonic and 24-h biofilm of S. mutans have been prepared in 96-cell microplates. These forms were treated by methylene blue (MB) and SeNPs and then were exposed to light-emitting diode (LED) lighting. Finally, the results have been reported as CFU/ml.

Results

The outcomes demonstrated that MB-induced PDT and SeNPs significantly reduced the number of planktonic bacteria (P-value < 0.001). The comparison between the treated and untreated groups showed that combining therapy with SeNPs and PDT remarkably decreased colony-forming units of one-day-old S. mutans biofilm (P-value < 0.05). The findings revealed that PDT modified by SeNPs had a high potential to destroy S. mutans biofilm. This combination therapy showed promising results to overcome oral infection in dental science.

Magnetic-Responsive Photosensitizer Nanoplatform for Optimized Inactivation of Dental Caries-Related Biofilms: Technology Development and Proof of Principle

Conventional antibiotic therapies for biofilm-trigged oral diseases are becoming less efficient due to the emergence of antibiotic-resistant bacterial strains. Antimicrobial photodynamic therapy (aPDT) is hampered by restricted access to bacterial communities embedded within the dense extracellular matrix of mature biofilms. Herein, a versatile photosensitizer nanoplatform (named MagTBO) was designed to overcome this obstacle by integrating toluidine-blue ortho (TBO) photosensitizer and superparamagnetic iron oxide nanoparticles (SPIONs) via a microemulsion method. In this study, we reported the preparation, characterization, and application of MagTBO for aPDT. In the presence of an external magnetic field, the MagTBO microemulsion can be driven and penetrate deep sites inside the biofilms, resulting in an improved photodynamic disinfection effect compared to using TBO alone. Besides, the obtained MagTBO microemulsions revealed excellent water solubility and stability over time, enhanced the aPDT performance against S. mutans and saliva-derived multispecies biofilms, and improved the TBO's biocompatibility. Such results demonstrate a proof-of-principle for using microemulsion as a delivery vehicle and magnetic field as a navigation approach to intensify the antibacterial action of currently available photosensitizers, leading to efficient modulation of pathogenic oral biofilms.

A nano phototheranostic approach of toluidine blue conjugated gold silver core shells mediated photodynamic therapy to treat diabetic foot ulcer

Diabetic foot infection caused by multidrug-resistant bacteria, is becoming serious problem. Moreover, polymicrobial biofilms contribute significantly to the persistent infections. In the present study, we investigated the effectiveness of novel toluidine blue conjugated chitosan coated gold-silver core-shell nanoparticles (TBO-chit-Au-AgNPs) mediated photodynamic therapy and demonstrate their use as a nontoxic antibacterial therapy to combat diabetic foot ulcer (DFU) caused by multi-drug resistant strains both in monomicrobial and polymicrobial state of infection. In vitro efficacy of TBO-chit-Au-AgNPs mediated photodynamic therapy (PDT) against polymicrobial biofilms was determined using standard plate count method and compared with that of monomicrobial biofilms of each species. Different anti-biofilm assays and microscopic studies were performed to check the efficacy of TBO-chit-Au-AgNPs mediated PDT, displayed significant decrease in the formation of biofilm. Finally, its therapeutic potential was validated in vivo type-2DFU. Cytokines level was found reduced, using nano-phototheranostic approach, indicating infection control. Expression profile of growth factors confirmed both the pathogenesis and healing of DFU. Hence, we conclude that TBO-chit-Au-AgNPs mediated PDT is a promising anti-bacterial therapeutic approach which leads to a synergistic healing of DFU caused by MDR bacterial strains.

Poly Lactic-co-Glycolic Acid-Coated Toluidine Blue Nanoparticles for the Antibacterial Therapy of Wounds

Bacterial infections in wounded skin are associated with high mortality. The emergence of drug-resistant bacteria in wounded skin has been a challenge. Toluidine blue (TB) is a safe and inexpensive photosensitizer that can be activated and used in near-infrared photodynamic therapy to effectively kill methicillin-resistant Staphylococcus aureus (MRSA). However, its aggregation-induced quenching effect largely affects its clinical applications. In this study, TB nanoparticles (NPs) were synthesized using an ultrasound-assisted coating method. Their physicochemical and biological properties were studied and evaluated by scanning electron microscopy and Fourier-transform infrared spectroscopy. The TBNPs had a broad-spectrum antibacterial activity against Gram-positive bacteria (MRSA) and Gram-negative bacteria (E. coli). In addition, MTT, hemolysis, and acute toxicity tests confirmed that TBNPs had good biocompatibility. The TBNPs exhibited a high photodynamic performance under laser irradiation and efficiently killed E. coli and MRSA through generated reactive oxygen species, which destroyed the cell wall structure. The potential application of TBNPs in vivo was studied using an MRSA-infected wound model. The TBNPs could promote wound healing within 7 days, mainly by reducing the inflammation and promoting collagen deposition and granulation tissue formation. In conclusion, the TBNPs offer a promising strategy for clinical applications against multiple-drug resistance.

The effect of photodynamic therapy by gold nanoparticles on Streptococcus mutans and biofilm formation: an in vitro study

In this experimental study, we aimed to evaluate the antibacterial and anti-biofilm effects of photodynamic therapy with a photosensitizer in conjunction with Gold nanoparticles against Streptococcus mutans as an important cariogenic bacterial agent. This experimental in vitro study evaluated the antibacterial and anti-biofilm effect of five groups as followed against S. mutans: methylene blue (MB), Gold nanoparticles (AuNPs), methylene blue conjugated with Gold nanoparticles (MB-AuNPs), MB mediated photodynamic therapy (MB mediated PDT) and methylene blue conjugated with Gold nanoparticles mediated photodynamic therapy (MB-AuNPs mediated PDT). InGaAlP laser (Azor-2 K) with 25 mW total output, 660 nm wavelength and laser probe cross-section of 0.78 cm² was used for methylene blue activation. Total dose of 19.23 J/cm² for 10 min was irradiated to each group. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and colony forming unit (CFU) were determined. Bacterial biofilm formation inhibition was assessed by crystal violet staining (The microtiter plate biofilm assay). The viability of S. mutans cells was assessed by MTT assay. MB mediated PDT and MB-AuNP mediated PDT were the most effective method for S. mutans biofilm inhibition (P < 0.05). MB alone, MB-AuNP alone and MB mediated PDT and MB-AuNP mediated PDT had the same effect against the planktonic phase of S. mutans (P > 0.05). Also they had similar pattern for bacterial growth inhibition and bactericidal effect (P > 0.05). Gold nano particle mediated photodynamic therapy represented antibacterial and antibiofilm activity against S. mutans; but this modality was not more effective than routine PDT.

Nanostructures as Targeted Therapeutics for Combating Oral Bacterial Diseases

Pathogenic oral biofilms are now recognized as a key virulence factor in many microorganisms that cause the heavy burden of oral infectious diseases. Recently, new investigations in the nanotechnology field have propelled the development of novel biomaterials and approaches to control bacterial biofilms, either independently or in combination with other substances such as drugs, bioactive molecules, and photosensitizers used in antimicrobial photodynamic therapy (aPDT) to target different cells. Moreover, nanoparticles (NPs) showed some interesting capacity to reverse microbial dysbiosis, which is a major problem in oral biofilm formation. This review provides a perspective on oral bacterial biofilms targeted with NP-mediated treatment approaches. The first section aims to investigate the effect of NPs targeting oral bacterial biofilms. The second part of this review focuses on the application of NPs in aPDT and drug delivery systems.

Antimicrobial photodynamic therapy (aPDT) against vancomycin resistant Staphylococcus aureus (VRSA) biofilm disruption: A putative role of phagocytosis in infection control

Biofilm mediated infections have major clinical impact. Staphylococcus aureus is a pathogen that frequently causes biofilm forming infections, such as those associated with medical devices and persistent wounds. Microorganisms embedded in biofilm are impervious to antibiotics and other antimicrobial agents, thus they are difficult to eliminate. The upsurge of multi-drug resistant strains makes treating such illnesses even more difficult. Therefore, new strategies are required to combat such type of infections. In this work, we have proposed an alternative therapeutic option to eradicate preformed biofilm of vancomycin resistant Staphylococcus aureus (VRSA) and enhanced phagocytosis by neutrophils in fresh human blood using curcumin mediated antimicrobial photodynamic therapy (aPDT).At sub-MIC of curcumin, different anti-biofilm assays and microscopic examinations were performed, followed by 20 J/cm² of blue laser light irradiation which corresponds to 52 s only. The result showed significant disruption of VRSA biofilm. Moreover, when curcumin-aPDT treated VRSA biofilm was exposed to whole blood from healthy donors, it was nearly completely eradicated. The present study suggests that curcumin-aPDT enhanced phagocytosis may be a useful strategy for inactivating VRSA biofilms adhering to medical implant surfaces.

Functionalized Nanoparticles Activated by Photodynamic Therapy as an Antimicrobial Strategy in Endodontics: A Scoping Review

The eradication of endodontic pathogens continues to be the focus of the search for new root canal system (RCS) disinfection strategies. This scoping review provides a comprehensive synthesis of antimicrobial photodynamic therapy (aPDT) using nanoparticles (NPs) as an alternative to optimize RCS disinfection. A systematic search up to March 2021 was carried out using the MEDLINE, EMBASE, Scopus, Lilacs, Central Cochrane Library, and BBO databases. We included studies focused on evaluating the activation of NPs by aPDT in inoculated root canals of human or animal teeth or bacterial cultures in the laboratory. The selection process and data extraction were carried out by two researchers independently. A qualitative synthesis of the results was performed. A total of seventeen studies were included, of which twelve showed a substantial antibacterial efficacy, two assessed the substantivity of the disinfection effect, and three showed low cytotoxicity. No adverse effects were reported. The use of functionalized NPs with photosensitizer molecules in aPDT has been shown to be effective in reducing the bacteria count, making it a promising alternative in endodontic disinfection. Further studies are needed to assess the development of this therapy in in vivo conditions, with detailed information about the laser parameters used to allow the development of safe and standardized protocols.

Photosensitization With Supramolecular Arrays for Enhanced Antimicrobial Photodynamic Treatments

Microbial infections represent a silent threat to health that has worsened in recent decades due to microbial resistance to multiple drugs, preventing the fight against infectious diseases. Therefore, the current postantibiotic era forces the search for new microbial control strategies. In this regard, antimicrobial photodynamic therapy (aPDT) using supramolecular arrays with photosensitizing capabilities showed successful emerging applications. This exciting field makes it possible to combine applied aspects of molecular photochemistry and supramolecular chemistry, together with the development of nano- and biomaterials for the design of multifunctional or "smart" supramolecular photosensitizers (SPS). This minireview aims to collect the concepts of the photosensitization process and supramolecular chemistry applied to the development of efficient applications of aPDT, with a brief discussion of the most recent literature in the field.

Antimicrobial effects of selenium nanoparticles in combination with photodynamic therapy against Enterococcus faecalis biofilm

BACKGROUND

Selenium Nanoparticles (SeNPs) were reported as an agent that may enhance the effectiveness of Photodynamic Antimicrobial Chemotherapy (PACT). This in vitro study evaluates the effect of SeNPs on the efficacy of Methylene Blue (MB)-induced PACT against the biofilm formated in 96-well plates and the dentine tubule biofilm of Enterococcus faecalis.

METHODS

Chitosan coated SeNPs were synthesized using chemical reduction method and were characterized by Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS). Twenty-four-hour biofilms of E. faecalis were developed on 96-well plates and treated with SeNPs, MB, and Light-Emitting Diode (LED). Also, three-week biofilms of E. faecalis were formed on 67 specimens of dentinal tubules, and the antibacterial effects of MB+SeNPs on these biofilms were studied.

RESULTS

The average hydrodynamic diameter of SeNPs was 80/3 nm according to DLS measurement. The combined use of MB and SeNPs significantly reduced Colony-Forming Units (CFUs) of one-day-old E. faecalis biofilms in comparison with the control group (P value < 0.05). Besides, combination therapy had the most antibacterial effect on root canal E. faecalis biofilms at both 200 and 400 µm depths of dentine tubules (P value < 0.001). Of note, about 50% of human fibroblast cells survived at a concentration of 128 µg/ml of SeNPs, compared to the control group.

CONCLUSION

The results demonstrated that the photodynamic therapy modified by SeNPs could be an effective disinfection alternative to the destruction of E. faecalis biofilms and root canal treatment.

Antibacterial Photodynamic Inactivation of Fagopyrin F from Tartary Buckwheat (Fagopyrum tataricum) Flower against Streptococcus mutans and Its Biofilm

The objective of this study was to determine reactive oxygen species (ROS) produced by fagopyrin F-rich fraction (FFF) separated from Tartary buckwheat flower extract exposed to lights and to investigate its antibacterial photodynamic inactivation (PDI) against Streptococcus mutans and its biofilm. ROS producing mechanisms involving FFF with light exposure were determined using a spectrophotometer and a fluorometer. S. mutans and its biofilm inactivation after PDI treatment of FFF using blue light (BL; 450 nm) were determined by plate count method and crystal violet assay, respectively. The biofilm destruction by ROS produced from FFF after exposure to BL was visualized using confocal laser scanning microscopy (CLSM) and field emission scanning electron microscope (FE-SEM). BL among 3 light sources produced type 1 ROS the most when applying FFF as a photosensitizer. FFF exposed to BL (5 and 10 J/cm2) significantly more inhibited S. mutans viability and biofilm formation than FFF without the light exposure (p < 0.05). In the PDI of FFF exposed to BL (10 J/cm2), an apparent destruction of S. mutans and its biofilm were observed by the CLSM and FE-SEM. Antibacterial PDI effect of FFF was determined for the first time in this study.

Phenothiazinium Photosensitizers Associated with Silver Nanoparticles in Enhancement of Antimicrobial Photodynamic Therapy

Antimicrobial photodynamic therapy (APDT) and silver nanoparticles (AgNPs) are known as promising alternatives for the control of microorganisms. This study aims to evaluate the antifungal activity of APDT, particularly by using the association of low concentrations of phenothiazinium photosensitizers (PS) methylene blue (MB), new methylene blue N (NMBN), and new methylene blue N Zinc (NMBN-Zn) in association with biosynthesized AgNPs. The AgNPs were characterized by UV-Vis spectrophotometry, transmission electron microscopy, and the dynamic light scattering method. The minimum inhibitory concentration of compounds in APDT against Candida albicans and Fusarium keratoplasticum was obtained and the Fractional Inhibitory Concentration Index determined the antifungal effect. The toxicity of compounds and associations in APDT were evaluated in Galleria mellonella. The AgNPs presented a surface plasmon band peak at 420 nm, hydrodynamic diameter of 86.72 nm, and zeta potential of -28.6 mV. AgNPs-PS showed a wider and displaced plasmon band peak due to PS ligands on the surface and decreased zeta potential. AgNPs-NMBN and AgNPs-NMBN-Zn associations presented synergistic effect in APDT with 15 J cm-2 against both fungi and did not show toxicity to G. mellonella. Hence, the enhancement of antifungal activity with low concentrations of compounds and absence of toxicity makes APDT with AgNPs-PS a promising therapeutic alternative for fungal infections.

Silver nanoprisms as plasmonic enhancers applied in the photodynamic inactivation of Staphylococcus aureus isolated from bubaline mastitis

Mastitis is a bacterial infection that affects all lactating mammals, and in dairy cattle, it leads to a reduction in their milk production and, in worse cases, it may lead to animal death. One viable therapeutic modality for overcoming bacterial resistance can be photodynamic inactivation (PDI), a therapeutic modality for bacterial infection treatment. One of the main factors that can lead to an efficient PDI process is the association of metallic nanoparticles in the close vicinity of photosensitizers, which has shown promising results due to localized surface plasmon resonance phenomena. In this work, methylene blue (MB) molecules were associated with Ag prismatic nanoplatelets (AgNPrs) to use as PDI photosensitizer against Staphylococcus aureus isolated from bubaline mastitis. The optical plasmonic activity of AgNPrs was tuned to the MB absorption region (600-700 nm) by inducing their growth into prismatic shapes by a seed-mediated procedure, using poly (sodium 4-styrene sulfonate) as the surfactant. A simulation on the plasmonic properties of the nanoprisms, applying particle size within the dimensions determined by TEM image analysis (d = 32 ± 6 nm), showed a 30 % increase of the incident field on the prismatic tips. Photodynamic results showed that the electrostatic AgNPr-MB conjugates promoted enhancement (ca. 15 %) of the reactive oxygen species production. Besides, PDI mediated by AgNPrs-MB led to the complete inactivation of the mastitis S. aureus strain after 6 min inactivation, in contrast to PDI mediated by MB, which reduced less than a 0.5 bacterial log. Thus, the results show this plasmonic enhanced photodynamic tool's potential to be applied in the inactivation of multi-resistant bacterial strains.

Microbes of the human eye: Microbiome, antimicrobial resistance and biofilm formation

BACKGROUND

The review focuses on the bacteria associated with the human eye using the dual approach of detecting cultivable bacteria and the total microbiome using next generation sequencing. The purpose of this review was to highlight the connection between antimicrobial resistance and biofilm formation in ocular bacteria.

METHODS

Pubmed was used as the source to catalogue culturable bacteria and ocular microbiomes associated with the normal eyes and those with ocular diseases, to ascertain the emergence of anti-microbial resistance with special reference to biofilm formation.

RESULTS

This review highlights the genetic strategies used by microorganisms to evade the lethal effects of anti-microbial agents by tracing the connections between candidate genes and biofilm formation.

CONCLUSION

The eye has its own microbiome which needs to be extensively studied under different physiological conditions; data on eye microbiomes of people from different ethnicities, geographical regions etc. are also needed to understand how these microbiomes affect ocular health.

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

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

Bacterial phototoxicity of biomimetic CdTe-GSH quantum dots

AIM

Fluorescent semiconductor nanoparticles or quantum dots (QDs) have excellent properties as photosensitizers in photodynamic therapy. This is mainly a consequence of their nanometric size and the generation of light-activated redox species. In previous works, we have reported the low-cost biomimetic synthesis of glutathione (GSH) capped QDs (CdTe-GSH QDs) with high biocompatibility. However, no studies have been performed to determine their phototoxic effect. The aim of this work was to characterize the light-induced toxicity of green (QDs₅₀₀ ) and red (QDs₆₀₀ ) QDs in Escherichia coli, and to study the molecular mechanism involved.

METHODS AND RESULTS

Photodegradation and reduction power of biomimetic QDs was determined to analyse their potential for radical generation. Escherichia coli cells were exposed to photoactivated QDs and viability was evaluated at different times. High toxicity was determined in E. coli cells exposed to photoactivated QDs, particularly QDs₅₀₀ . The molecular mechanism involved in QDs phototoxicity was studied by determining Cd²⁺ -release and intracellular reactive oxygen species (ROS). Cells exposed to photoactivated QDs₅₀₀ presented high levels of ROS. Cells exposed to photoactivated QDs₅₀₀ presented high levels of ROS. Finally, to understand this phenomenon and the importance of oxidative and cadmium-stress in QDs-mediated phototoxicity, experiments were performed in E. coli mutants in ROS and Cd²⁺ response genes. As expected, E. coli mutants in ROS response genes were more sensitive than the wt strain to photoactivated QDs, with a higher effect in green-QDs₅₀₀ . No increase in phototoxicity was observed in cadmium-related mutants.

CONCLUSION

Obtained results indicate that light exposure increases the toxicity of biomimetic QDs on E. coli cells. The mechanism of bacterial phototoxicity of biomimetic CdTe-GSH QDs is mostly associated with ROS generation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results presented establish biomimetic CdTe-GSH QDs as a promising cost-effective alternative against microbial infections, particularly QDs₅₀₀ .

Light Energy Dose and Photosensitizer Concentration Are Determinants of Effective Photo-Killing against Caries-Related Biofilms

Caries-related biofilms and associated complications are significant threats in dentistry, especially when biofilms grow over dental restorations. The inhibition of cariogenic biofilm associated with the onset of carious lesions is crucial for preventing disease recurrence after treatment. This in vitro study defined optimized parameters for using a photosensitizer, toluidine blue O (TBO), activated via a red light-emitting diode (LED)-based wireless device to control the growth of cariogenic biofilms. The effect of TBO concentrations (50, 100, 150, and 200 μg/mL) exposed to light or incubated in the dark was investigated in successive cytotoxicity assays. Then, a mature Streptococcus mutans biofilm model under sucrose challenge was treated with different TBO concentrations (50, 100, and 150 μg/mL), different light energy doses (36, 108, and 180 J/cm²), and different incubation times before irradiation (1, 3, and 5 min). The untreated biofilm, irradiation with no TBO, and TBO incubation with no activation represented the controls. After treatments, biofilms were analyzed via S. mutans colony-forming units (CFUs) and live/dead assay. The percentage of cell viability was within the normal range compared to the control when 50 and 100 μg/mL of TBO were used. Increasing the TBO concentration and energy dose was associated with biofilm inhibition (p < 0.001), while increasing incubation time did not contribute to bacterial elimination (p > 0.05). Irradiating the S. mutans biofilm via 100 μg/mL of TBO and ≈180 J/cm² energy dose resulted in ≈3-log reduction and a higher amount of dead/compromised S. mutans colonies in live/dead assay compared to the control (p < 0.001). The light energy dose and TBO concentration optimized the bacterial elimination of S. mutans biofilms. These results provide a perspective on the determining parameters for highly effective photo-killing of caries-related biofilms and display the limitations imposed by the toxicity of the antibacterial photodynamic therapy’s chemical components. Future studies should support investigations on new approaches to improve or overcome the constraints of opportunities offered by photodynamic inactivation of caries-related biofilms.

Propolis nanoparticle enhances the potency of antimicrobial photodynamic therapy against Streptococcus mutans in a synergistic manner

Less invasive removal approaches have been recommended for deep caries lesions. Antimicrobial photodynamic therapy (aPDT) and propolis nanoparticle (PNP) are highlighted for the caries management plan. Evidence is lacking for an additive effect of combination PNP with photosensitizer (PS) in aPDT. This study aimed to investigate the individual and synergistic effects of chlorophyllin-phycocyanin mixture (PhotoActive⁺) and toluidine blue O (TBO) as PSs in combination with PNP in the aPDT process (aPDT^plus) against major important virulence factors of Streptococcus mutans. Following characterization, biocompatibility of the PSs alone, or in combination with PNP were investigated on human gingival fibroblast cell. The in vitro synergy of PhotoActive⁺ or TBO and PNP was evaluated by the checkerboard method. The bacteria's virulence properties were surveyed in the presence of the PSs, individually as well as in combination. When the PSs were examined in combination (synergistic effect, FIC Index < 0.5), a stronger growth inhibitory activity was exhibited than the individual PSs. The biofilm formation, as well as genes involved in biofilm formation, showed greater suppression when the PSs were employed in combination. Overall, the results of this study suggest that the combination of PhotoActive⁺ or TBO with PNP with the least cytotoxicity effects and the highest antimicrobial activites would improve aPDT outcomes, leading to synergistic effects and impairing the virulence of S. mutans.

Photodynamic antimicrobial chemotherapy (PACT) using riboflavin inhibits the mono and dual species biofilm produced by antibiotic resistant Staphylococcus aureus and Escherichia coli

PURPOSE

Multispecies biofilms play a significant role in persistent infections. Furthermore, by interspecies transfer of antibiotic resistance genes, multispecies biofilms spread antibiotic resistance. The purpose of this study was to investigate the effect of Photodynamic Antimicrobial Chemotherapy (PACT) using riboflavin on mono and multi species biofilms.

METHODS

For this we used two clinically relevant opportunistic pathogens species E. coli and S. aureus as mono-species and multispecies biofilms. We did broth dilution assay for antibacterial, crystal violet assay for biofilms and fluorometric study for reactive oxygen species (ROS) and extracellular polymeric substance (EPS) production by phenol-HCl method.

RESULTS

Antibacterial study revealed that photo-illuminated riboflavin shows bactericidal effect against each bacteria and their mix culture. E. coli was found to be little more resistant than S. aureus. Crystal violet assay revealed photo-illuminated riboflavin shows anti-biofilms activity against both mono and mix species biofilms. But mix species biofilms were more resistant to PACT than mono species biofilms. Further study revealed this may be due to the interaction between different EPS production, hence in mix species biofilms EPS production is less affected after PACT than mono species biofilms. We found photo-illuminated riboflavin increased the intracellular ROS production.

CONCLUSION

Photo-illuminated riboflavin shows bactericidal and anti-biofilms effect against each bacteria and their mix culture. Photo-illuminated increased intracellular ROS production, which may induce the oxidative stress and destroy the respiratory system of bacteria.

Biogenic Silver Nanoparticles Decorated with Methylene Blue Potentiated the Photodynamic Inactivation of Pseudomonas aeruginosa and Staphylococcus aureus

The persistence of multidrug resistance among microorganisms has directed a mandate towards a hunt for the development of alternative therapeutic modalities. In this context, antimicrobial photodynamic therapy (aPDT) is sprouted as a novel strategy to mitigate biofilms and planktonic cells of pathogens. Nanoparticles (NPs) are reported with unique intrinsic and antimicrobial properties. Therefore, silver NPs (AgNPs) were investigated in this study to determine their ability to potentiate the aPDT of photosensitizer against Staphylococcus aureus and Pseudomonas aeruginosa. Biologically synthesized AgNPs were surface coated with methylene blue (MB) and studied for their aPDT against planktonic cells and biofilms of bacteria. The nano-conjugates (MB-AgNPs) were characterized for their size, shape and coated materials. MB-AgNPs showed significant phototoxicity against both forms of test bacteria and no toxicity was observed in the dark. Moreover, activity of MB-AgNPs was comparatively higher than that of the free MB, which concludes that MB-AgNPs could be an excellent alternative to combat antibiotic resistant bacteria.

Prospects on Nano-Based Platforms for Antimicrobial Photodynamic Therapy Against Oral Biofilms

Objective: This review clusters the growing field of nano-based platforms for antimicrobial photodynamic therapy (aPDT) targeting pathogenic oral biofilms and increase interactions between dental researchers and investigators in many related fields. Background data: Clinically relevant disinfection of dental tissues is difficult to achieve with aPDT alone. It has been found that limited penetrability into soft and hard dental tissues, diffusion of the photosensitizers, and the small light absorption coefficient are contributing factors. As a result, the effectiveness of aPDT is reduced in vivo applications. To overcome limitations, nanotechnology has been implied to enhance the penetration and delivery of photosensitizers to target microorganisms and increase the bactericidal effect. Materials and methods: The current literature was screened for the various platforms composed of photosensitizers functionalized with nanoparticles and their enhanced performance against oral pathogenic biofilms. Results: The evidence-based findings from the up-to-date literature were promising to control the onset and the progression of dental biofilm-triggered diseases such as dental caries, endodontic infections, and periodontal diseases. The antimicrobial effects of aPDT with nano-based platforms on oral bacterial disinfection will help to advance the design of combination strategies that increase the rate of complete and durable clinical response in oral infections. Conclusions: There is enthusiasm about the potential of nano-based platforms to treat currently out of the reach pathogenic oral biofilms. Much of the potential exists because these nano-based platforms use unique mechanisms of action that allow us to overcome the challenging of intra-oral and hard-tissue disinfection.

bolA gene involved in curli amyloids and fimbriae production in E. coli: exploring pathways to inhibit biofilm and amyloid formation

Background

Biofilm formation is a complex phenomenon of bacterial cells, involved in several human infections. Its formation is regulated and controlled by several protein factors. The BolA-like proteins (bolA gene) are conserved in both prokaryotes and eukaryotes. The BolA protein is a transcription factor involved in bacterial cell motility and biofilm formation. This study was initiated to elucidate the role of the bolA gene in the curli biogenesis and amyloid production as well as to observe changes in the expression of fimH, a fimbriae gene.

Methods

Knockdown mutants of Escherichia coli MG1655 bolA gene (bolA-KD) were generated using CRISPR interference. The results obtained, were validated through gene expression using RT-PCR, microscopic analysis and different biofilm and amyloid assays.

Results

The bolA knockdown mutants showed a decrement in curli amyloid fibers, in fimbriae production and biofilm formation. We have also observed a reduction in EPS formation, eDNA production and extracellular protein content. Gene expression data showed that bolA downregulation caused the suppression of csgA and csgD of curli that led to the reduction in curli fiber and the amyloid formation and also the suppression of fimH, leading to the loss of fimbriae.

Conclusions

Curli fibers and fimbriae are found to be involved in biofilm formation leading to the pathogenicity of the bacterial cell. BolA is a conserved protein and is found to play a significant role in curli and fimbriae formation in E. coli. This study further proved that CRISPRi mediated suppression of the bolA gene leads to inhibition of biofilm formation through curli and fimbriae inhibition. Hence, it may be proposed as a possible target for intervention of biofilm mediated infections.

Exploring antibiofilm potential of bacitracin against streptococcus mutans

Bacitracin has well familiar effects on growth and colonization of bacteria but its antibiofilm action on majority of bacteria is still not studied. Bacitracin is a bactericidal antibiotic that primarily acts on Gram positive bacteria by obstructing the process of cell wall synthesis. In this study, we have investigated antibiofilm potential and the mechanism of bacitracin against a cariogenic bacteria 'Streptococcus mutans' which has not been reported so far. Bacitracin has been found to affect propensity of S. mutans to form biofilm. On treatment with sub-MIC concentration of bacitracin resulted in significant reduction in bifilm formation as evaluated by crystal violet and congo red assays. The architecture of S. mutans biofilm was observed by scanning electron microscopy which revealed astonishing phenotype of biofilm. Deficient biofilm was found to be composed of abnormally elongated cells. Transmission electron microscopy showed multiple septa formation in each cell of biofilm thereby indicating, cell division defect as the most probable cause of cell elongation. To elucidate the effect of bacitracin on molecular level, expression profiling of genes critically important for cell division and biofilm formation was performed, which were found many folds downregulated. Bacitracin at very low concentration has been found to have potent antibiofilm activity, therefore is a potential antibiofilm agent to treat oral biofilms. It is being anticipated, this study will offer novel information to identify potential targets and effectively creates true innovation to understand the biofilm's basic biology. Besides, discovering new uses for currently marketed drugs makes commercial as well as research sense.

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

OBJECTIVE

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Anti-biofilm and anti-metabolic effects of antimicrobial photodynamic therapy using chlorophyllin-phycocyanin mixture against Streptococcus mutans in experimental biofilm caries model on enamel slabs

BACKGROUND

Partial (selective) removal of dental caries is a suitable manner to treat deep carious lesions in vital teeth with asymptomatic pulps. Antimicrobial photodynamic therapy (aPDT) was proposed as a promising ancillary approach for reduction of the residual bacteria from the cavity. Therefore, the focus of this study was to investigate the influence of aPDT using diode laser (DL) plus PhotoActive+ (chlorophyllin-phycocyanin mixture [CHL-PC]) as photosensitizer (PS) on metabolic activity and the reduction in the number of living bacteria within the preformed biofilm caries model on enamel slabs of Streptococcus mutans.

MATERIALS AND METHODS

The lethal and sub-significant inhibitory (SSI) potential of aPDT using CHL-PC and 635 nm DL against experimental biofilm caries model on enamel slabs and metabolic activity of S. mutans was analyzed using crystal violet and XTT reduction assays, respectively. Intracellular ROS formation by DCFH-DA assay was measured in CHL-PC mediated aPDT treated bacterial samples. Tooth discoloration and cell cytotoxicity of CHL-PC were assessed in the CIEL*a*b* color space and neutral red assay, respectively.

RESULTS

In this study aPDT at a maximum concentration level of CHL-PC (5000 μg/mL) with 3 min DL irradiation time (103.12 J/cm²) reduced the ex-vivo cariogenic biofilm of S. mutans by 36.93 % (P <  0.05). Although chlorhexidine (CHX) had an anti-biofilm effect about 1.7 fold compared to CHL-PC mediated aPDT, this difference was not significant (36.93 in comparison to 63.05 %; P >  0.05). CHL-PC mediated aPDT demonstrated a significant reduction in bacterial metabolic activity, with rates of 77 % at a SSI dose (using 156 μg/mL of CHL-PC and 3 min DL irradiation time with the energy density of 103.12 J/cm²). The treated bacterial cells exhibited significant (P < 0.05) increment in the ROS generation. The least color change (ΔE) was found using CHL-PC at a concentration of 156 μg/mL (ΔE = 2.74). CHL-PC in different concentrations showed no significant reduction in human gingival fibroblasts (HGFs) cell survival (P >  0.05).

CONCLUSION

CHL-PC mediated aPDT not only reduces the number of living bacteria within the biofilms of S. mutans in an experimental biofilm caries model on enamel slabs but also its influences microbial virulence by reducing the metabolic activity of the S. mutants.

Nanocarriers in photodynamic therapy-in vitro and in vivo studies

Photodynamic therapy (PDT) is a minimally invasive technique which has proven to be successful in the treatment of several types of tumors. This relatively simple method exploits three inseparable elements: phototoxic compound (photosensitizer [PS]), light source, and oxygen. Upon irradiation by light with specified wavelength, PS generates reactive oxygen species, which starts the cascade of reactions leading to cell death. The positive therapeutic outcome of PDT may be limited due to several aspects, including low water solubility of PSs, hampering their effective administration and blood circulation, as well as low tumor specificity, inefficient cellular uptake and activation energies requiring prolonged illumination times. One of the promising approaches to overcome these obstacles involves the use of carrier systems modulating pharmacokinetics and pharmacodynamics of the PSs. In the present review, we summarized current in vitro and in vivo studies regarding the use of nanoparticles as potential delivery devices for PSs to enhance their cellular uptake and cytotoxic properties, and thus-the therapeutic outcome of PDT. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Antimicrobial photodynamic therapy on Staphylococcus aureus and Escherichia coli using malachite green encapsulated mesoporous silica nanoparticles: an in vitro study

Background

Rise in the number of healthcare associated or hospital acquired infections is a major problem affecting the global healthcare sector. We evaluated superior antibacterial and antibiofilm photodynamic therapy (aPDT) using malachite green encapsulated mesoporous silica nanoparticles (MG-MSN) against Staphylococcus aureus and Escherichia coli, which are known to be major causative agents of nosocomial infections.

Methods

Malachite green (MG) was encapsulated on mesoporous silica nanoparticles (MSN). Fourier-transform infrared spectroscopy, Transmission electron microscopy, and spectroscopic analysis were performed to characterize the MG-MSN. The antimicrobial efficacies of MSN, MG, and MG-MSN were investigated and the results were recorded.

Results

MG-MSN was effective against both the tested bacteria. S. aureus was more phototoxic to MG-MSN compared to E. coli. The antibiofilm efficacy of MG-MSN on E. coli and S. aureus was also studied. Biofilm inhibition was 65.68 ± 2.62% in E. coli and 79.66 ± 3.82% in S. aureus. Cell viability assay, exopolysaccharides quantification, and confocal laser scanning microscopy studies also revealed the enhanced antibiofilm activity of MG-MSN when used as a potential photosensitizer for aPDT. This study can be extended to eradicate these strains from localized superficial infections and medical appliances, preventing nosocomial infections.

Novel nanomaterial-based antibacterial photodynamic therapies to combat oral bacterial biofilms and infectious diseases

Oral diseases such as tooth caries, periodontal diseases, endodontic infections, etc., are prevalent worldwide. The heavy burden of oral infectious diseases and their consequences on the patients' quality of life indicates a strong need for developing effective therapies. Advanced understandings of such oral diseases, e.g., inflammatory periodontal lesions, have raised the demand for antibacterial therapeutic strategies, because these diseases are caused by viruses and bacteria. The application of antimicrobial photodynamic therapy (aPDT) on oral infectious diseases has attracted tremendous interest in the past decade. However, aPDT had a minimal effect on the viability of organized biofilms due to the hydrophobic nature of the majority of the photosensitizers (PSs). Therefore, novel nanotechnologies were rapidly developed to target the delivery of hydrophobic PSs into microorganisms for the antimicrobial performance improvement of aPDT. This review focuses on the state-of-the-art of nanomaterials applications in aPDT against oral infectious diseases. The first part of this article focuses on the cutting-edge research on the synthesis, toxicity, and therapeutic effects of various forms of nanomaterials serving as PS carriers for aPDT applications. The second part discusses nanomaterials applications for aPDT in treatments of oral diseases. These novel bioactive nanomaterials have demonstrated great potential to serve as carriers for PSs to substantially enhance the PDT therapeutic effects. Furthermore, the novel aPDT applications not only have exciting therapeutic potential to inhibit bacterial plaque-initiated oral diseases, but also have a wide applicability to other biomedical and tissue engineering applications.

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.

Antimicrobial photodynamic activity of toluidine blue-carbon nanotube conjugate against Pseudomonas aeruginosa and Staphylococcus aureus - Understanding the mechanism of action

BACKGROUND

The emergence of drug-resistant bacterial strains has raised the need to develop alternative treatment modalities to combat infectious diseases. Antimicrobial photodynamic therapy (aPDT) is an alternative to conventional treatment modalities. aPDT integrates a photosensitizer, which, after exposure to light of an appropriate wavelength, leads to the generation of cytotoxic reactive oxygen species (ROS).

METHODS

The aim of the present study was to synthesize a toluidine blue/multiwalled carbon nanotube conjugate (TBCNT) for enhanced photoinactivation of Pseudomonas aeruginosa and Staphylococcus aureus. Synthesized TBCNT conjugate was characterized and its antibacterial and antibiofilm activity was determined.

RESULTS

During TBCNT synthesis, dye loading, and entrapment efficiency of the CNT were 12.04 ± 0.55% and 48.99 ± 2.33%, respectively. The photo-destruction of planktonic cells of the test bacteria was performed by exposure to a 125 mW red laser with a wavelength of 670 nm (radiant exposure of 58.49 J/cm²) for 3 min. Photoinactivation using TBCNT resulted in a 4.91- and 5.47-log10 reduction in P. aeruginosa and S. aureus, respectively. The mechanism of this aPDT was studied by measuring intracellular ROS generation, protein leakage, and lipid peroxidation in the test bacteria after light irradiation. The antibiofilm activity of TBCNT after light exposure was 69.94% and 75.54% for P. aeruginosa and S. aureus, respectively. Photoinactivation of test bacteria treated with TBCNT reduced cell viability and exopolysaccharide production. Confocal laser-scanning microscopy revealed a significant biofilm inhibition efficacy of the TBCNT conjugate.

CONCLUSION

Therefore, TBCNT conjugates may be used for the eradication of P. aeruginosa and S. aureus biofilms.

Malachite green-conjugated multi-walled carbon nanotubes potentiate antimicrobial photodynamic inactivation of planktonic cells and biofilms of Pseudomonas aeruginosa and Staphylococcus aureus

Purpose: Infections associated with medical devices that are caused by biofilms remain a considerable challenge for health care systems owing to their multidrug resistance patterns. Biofilms of Pseudomonas aeruginosa and Staphylococcus aureus can result in life-threatening situations which are tough to eliminate by traditional methods. Antimicrobial photodynamic inactivation (aPDT) constitutes an alternative method of killing deadly pathogens and their biofilms using reactive oxygen species (ROS). This study investigated the efficacy of enhanced in vitro aPDT of P. aeruginosa and S. aureus using malachite green conjugated to carboxyl-functionalized multi-walled carbon nanotubes (MGCNT). Both the planktonic cells and biofilms of test bacteria were demonstrated to be susceptible to the MGCNT conjugate. These MGCNT conjugates may thus be employed as a facile strategy for designing antibacterial and anti-biofilm coatings to prevent the infections associated with medical devices. Methods: Conjugation of the cationic dye malachite green to carbon nanotube was studied by UV-visible spectroscopy, high-resolution transmission electron microscopy, and Fourier transform infrared spectrometry. P. aeruginosa and S. aureus photodestruction were studied using MGCNT conjugate irradiated for 3 mins with a red laser of wavelength 660 nm and radiant exposure of 58.49 J cm^-2. Results: Upon MGCNT treatment, S. aureus and P. aeruginosa were reduced by 5.16 and 5.55 log₁₀ , respectively. Compared to free dye, treatment with MGCNT afforded improved phototoxicity against test bacteria, concomitant with greater ROS production. The results revealed improved biofilm inhibition, exopolysaccharide inhibition, and reduced cell viability in test bacteria treated with MGCNT conjugate. P. aeruginosa and S. aureus biofilms were considerably reduced to 60.20±2.48% and 67.59±3.53%, respectively. Enhanced relative MGCNT phototoxicity in test bacteria was confirmed using confocal laser scanning microscopy. Conclusion: The findings indicated that MGCNT conjugate could be useful to eliminate the biofilms formed on medical devices by S. aureus and P. aeruginosa.

Antibiotics versus biofilm: an emerging battleground in microbial communities

Biofilm is a complex structure of microbiome having different bacterial colonies or single type of cells in a group; adhere to the surface. These cells are embedded in extracellular polymeric substances, a matrix which is generally composed of eDNA, proteins and polysaccharides, showed high resistance to antibiotics. It is one of the major causes of infection persistence especially in nosocomial settings through indwelling devices. Quorum sensing plays an important role in regulating the biofilm formation. There are many approaches being used to control infections by suppressing its formation but CRISPR-CAS (gene editing technique) and photo dynamic therapy (PDT) are proposed to be used as therapeutic approaches to subside bacterial biofim infections, especially caused by deadly drug resistant bad bugs.

Photoinactivation of ESKAPE pathogens: overview of novel therapeutic strategy

The emergence of antimicrobial drug resistance requires development of alternative therapeutic options. Multidrug-resistant strains of Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa and Enterobacter spp. are still the most commonly identified antimicrobial-resistant pathogens. These microorganisms are part of the so-called 'ESKAPE' pathogens to emphasize that they currently cause the majority of hospital acquired infections and effectively 'escape' the effects of antibacterial drugs. Thus, alternative, safer and more efficient antimicrobial strategies are urgently needed, especially against 'ESKAPE' superbugs. Antimicrobial photodynamic inactivation is a therapeutic option used in the treatment of infectious diseases. It is based on a combination of a photosensitizer, light and oxygen to remove highly metabolically active cells.