Photodynamic and peptide-based strategy to inhibit Gram-positive bacterial biofilm formation

The Effect of Photodynamic Therapy on Enterococcus spp. and Its Application in Dentistry: A Scoping Review

Enterococci spp. are Gram-positive bacteria that cause mild to severe infections, many associated with the oral cavity, such as periapical infections and healthcare-associated infections (HAIs). Many of these infections become serious diseases that are difficult to resolve, specifically when multidrug-resistant (MDR) strains cause them. In recent years, the number of MDR strains of Enterococcus spp. has increased significantly. This increased prevalence of MDR strains produces significant pressure to generate more antimicrobial therapies, but there is a decline in the production of new antibiotics, driving the development of complementary therapies, such as photodynamic therapy (PDT). PDT combines a photosensitizer agent (PS), light, and oxygen to cause photooxidative stress in bacterial cells. PDT can eradicate Enterococcus spp. contaminations, improve the classic cleaning processes, and eradicate the bacteria in dental pieces. PDT's effectiveness can be improved with nanoparticles that function as carriers. Our work aims to describe the advances in PDT against Enterococcus spp. as a complement to antibiotic therapy, focusing on infections by Enterococcus faecium and Enterococcus faecalis, dental hygiene, and using nanoparticles to improve the antimicrobial effect. A systematic bibliographic search without a meta-analysis was conducted on various databases, using inclusion and exclusion criteria to identify the most relevant research. Of the 193 non-redundant articles found, 65 were selected for a systematic review, from which a summary table was created and a manual description was made. Photodynamic therapy for treating E. faecium and E. faecalis is a widely studied area, with promising results concerning bactericidal effectiveness and reductions in biofilm formation, particularly in regard to dental hygiene. Because most of the studies were conducted in vitro or ex vivo, the results indicated that there were not sufficient data to initiate clinical trials for safety and efficacy studies on humans.

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.

Chlorin-e6 conjugated to the antimicrobial peptide LL-37 loaded nanoemulsion enhances photodynamic therapy against multi-species biofilms related to periodontitis

In our previous studies, Chlorin-e6 (Ce6) demonstrated a significant reduction of microorganisms' viability against multi-species biofilm related to periodontitis while irradiated with blue light. However, the conjugation of Ce6 and antimicrobial peptides, and the incorporation of this photosensitizer in a nanocarrier, is still poorly explored. We hypothesized that chlorin-e6 conjugated to the antimicrobial peptide LL-37 loaded nanoemulsion could inhibit a multi-species biofilm related to periodontitis during photodynamic therapy (PDT), the pre-treatment with hydrogen peroxide was also tested. The nanoemulsion (NE) incorporated with Ce6 was characterized regarding the physiochemical parameters. Images were obtained by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Later, the Ce6 and LL-37 incorporated in NE was submitted to UV-Vis analysis and Reactive Oxygen Species (ROS) assay. Finally, the combined formulation (Ce6+LL-37 in nanoemulsion) was tested against multi-species biofilm related to periodontitis. The formed nanoformulation was kinetically stable, optically transparent with a relatively small droplet diameter (134.2 unloaded and 146.9 loaded), and weak light scattering. The NE system did not impact the standard UV-VIS spectra of Ce6, and the ROS production was improved while Ce6 was incorporated in the NE. The combination of Ce6 and LL-37 in NE was effective to reduce the viability of all bacteria tested. The treatment with hydrogen peroxide previous to PDT significantly impacted bacterial viability. The current aPDT regimen was the best already tested against periodontal biofilm by our research team. Our results suggest that this combined protocol must be exploited for clinical applications in localized infections such as periodontal disease. - Nanoemulsion demonstrated to be an excellent nanocarrier for photodynamic application. - Chlorin-e6 incorporated in nanoemulsion showed great physicochemical and biophotonic parameters. - The combination of chlorin-e6 and LL-37 peptide in nanoemulsion is effective to eliminate periodontal pathogenic bacteria. - The treatment with hydrogen peroxide previous to PDT significantly impacted bacterial viability.

Sonophotodynamic inactivation of Pseudomonas aeruginosa biofilm mediated by curcumin

The inactivation of Pseudomonas aeruginosa biofilm is a major challenge, as biofilms are less responsive to conventional treatments and responsible for persistent infections. This has led to the investigation of alternative approaches for biofilm control such as photodynamic (PDI) and sonodynamic (SDI) inactivation. The combination of them, known as Sonophotodynamic Inactivation (SPDI), has improved the effectiveness of the process. Curcumin, a well-established photosensitizer, has been identified as a potential sonosensitizer. This study evaluated the most effective combination for SPDI against P. aeruginosa biofilms in vitro, varying curcumin concentrations and ultrasound intensities. The results indicated that the inactivation was directly proportional to the curcumin concentration. Using curcumin 120 µM and 3.0 W.cm-2 of ultrasound intensity, SPDI demonstrated the highest and the best synergistic results, equivalent to 6.9 ± 2.1 logs of reduction. PDI reduced 0.7 ± 0.9 log and SDI had no effect. In conclusion, SPDI with curcumin is a promising approach for biofilm inactivation.

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.

The structure and matrix dynamics of bacterial biofilms as revealed by antimicrobial peptides' diffusion

From the biological point of view, bacterial biofilms are communities of bacteria embedded in a self-produced gel matrix composed of polysaccharides, DNA, and proteins. Considering the biophysical point of view, the biofilm matrix is a highly dense, crowded medium that imposes constraints to solute diffusion, depending on the size, conformational dynamics, and net charge. From the pharmacological point of view, biofilms are additional difficulties to drug development as heterogeneity in oxygen and nutrient distribution, and consequently, heterogeneity in bacterial metabolic status leads to recalcitrance. For peptide scientists, biofilms are both a challenge and an opportunity. Biofilms can be intruded by peptides, revealing important biological, biophysical, and pharmacological insights. Peptides can be engineered for different sizes, flexibilities, and net charges, unravelling the determinants of diffusion; they kill bacteria by lysis, overcoming the hurdles of metabolic status heterogeneity, and they are able to kill bacteria in the biofilm core, leaving the matrix intact, that is, without causing bacterial biofilm dispersion as side effect. This concise review addresses the knowledge reached while interrogating bacterial biofilms with peptides and other reporter molecules, and the advances therefrom in biology, biophysics, and drug development.

A conjugate of chlorin e6 and cationic amphipathic peptoid: a dual antimicrobial and anticancer photodynamic therapy agent

Cationic amphipathic structures are often utilized in natural membrane-active host-defense peptides. Negatively charged surface membranes of rapidly proliferating bacterial and cancer cells have been targeted by various synthetic peptides and peptidomimetics adopting the structural motif. Herein, we synthesized a set of conjugates composed of cationic amphipathic peptoids (i.e., oligo-N-substituted glycines) and a chlorin photosensitizer, named chlorin e6 (Ce6)-peptoid conjugates (CPCs). Among the nine CPCs, CPC 7, composed of Ce6, a PEG linker, and guanidine-rich helical amphipathic peptoids, exhibited a distinct photoresponsive inactivation of Gram-positive and Gram-negative bacteria. Subsequent studies showed that CPC 7 effectively killed various cancer cells after irradiation with red light (655 nm), suggesting the potential of CPC 7 as a dual antimicrobial and anticancer agent. Confocal laser scanning microscopy and flow cytometry data suggested that CPC 7 could induce apoptotic cell death. Our results show the potential of peptoid-based photosensitizer conjugates as a versatile platform for antimicrobial and anticancer photodynamic therapy agents and peptoid therapeutics.

Efficacy of the combination of P5 peptide and photodynamic therapy mediated by bixin and chlorin-e6 against Cutibacterium acnes biofilm

In this study, the action of antimicrobial peptide (AMP) P5 and antimicrobial photodynamic therapy (aPDT) mediated by bixin and chlorin-e6 (Ce6) on Cutibacterium acnes (C. acnes) in planktonic phase and biofilm were evaluated both as monotherapies and combined therapies. Microbial viability after treatments were quantified by colony-forming units per milliliter of the sample (CFU/mL) and have demonstrated that all treatments employed exerted bactericidal activity, reducing the microbial load by more than 3 log₁₀ CFU/mL, also demonstrating for the first time in the literature the antimicrobial photodynamic effect of bixin that occurs mostly through type I mechanism which was proved by the quantification of superoxide anion production. Bacterial biofilm was completely eliminated only after its exposure to aPDT mediated by this PS, however, Ce6 proved to be a more efficient PS, considering that most of the photodynamic effect of bixin- aPDT was exerted by excitation of the endogenous C porphyrins of C. acnes with blue light. The combination of P5 with Ce6-aPDT showed a synergistic effect on the bacterial biofilm with a reduction in microbial load by more than 10 log₁₀ CFU/mL, in which the ability of P5 to permeabilize the polymeric extracellular matrix of the biofilm explains the obtained results, with greater internalization of the PS as shown by the Confocal Laser Scanning Microscopy. One-way ANOVA (Analysis of Variance) with Tukey's post-test and two-way ANOVA with Bonferroni's post-test were used to compare the values of continuous variables between the control group and the treatment groups.

Photodynamic therapy-a promising treatment of oral mucosal infections

The treatment of oral mucosal infections is increasingly challenging owing to antibiotic resistance. Therefore, alternative antimicrobial strategies are urgently required. Photodynamic therapy (PDT) has attracted attention for the treatment of oral mucosal infections because of its ability to effectively inactivate drug-resistant bacteria, completely heal clinical infectious lesions and usually offers only mild adverse reactions. This review briefly summarizes relevant scientific data and published papers and discusses the potential mechanism and application of PDT in the treatment of oral mucosal infections.

Use of Photodynamic Therapy Associated with Antimicrobial Peptides for Bacterial Control: A Systematic Review and Meta-Analysis

Considering the challenges related to antimicrobial resistance, other strategies for controlling infections have been suggested, such as antimicrobial photodynamic therapy (aPDT) and antimicrobial peptides (AMP). This study aims to perform a systematic review and meta-analysis to obtain evidence on the antimicrobial effectiveness of aPDT associated with AMP and establish in vitro knowledge on this topic for further study designs. The PubMed, Scopus, Web of Science, Science Direct, Scielo, and Cochrane Library databases were searched. Two independent and calibrated researchers (Kappa = 0.88) performed all the systematic steps according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The odds ratio (OR) was used as the effect measure. The Peto method was used to perform the meta-analysis due to the sparse data. Twenty studies were included in the present review. The result was significant (OR = 0.14/p = 0.0235/I-squared = 0%), showing better outcomes of aPDT associated with peptides than those of aPDT alone for controlling the microbial load. Only 20% of the studies included evaluated this approach in a biofilm culture. Combined treatment with aPDT and AMP highly increased the ability of microbial reduction of Gram-positive and Gram-negative bacteria. However, additional blind studies are required to evaluate the efficacy of this therapy on microbial biofilms.

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.

Photodynamic Inactivation of an Endodontic Bacteria Using Diode Laser and Indocyanine Green-Loaded Nanosphere

Apical periodontitis, an inflammatory lesion causing bone resorption around the apex of teeth, is treated by eradicating infectious bacteria from the root canal. However, it has a high recurrence rate and often requires retreatment. We investigated the bactericidal effect of antimicrobial photodynamic therapy (aPDT)/photodynamic antimicrobial chemotherapy (PACT) using indocyanine green (ICG)-loaded nanospheres coated with chitosan and a diode laser on a biofilm of Enterococcus faecalis, a pathogen of refractory apical periodontitis. Biofilm of E. faecalis was cultured in a porcine infected root canal model. ICG solution was injected into the root canal, which was then irradiated with a laser (810 nm wavelength) from outside the root canal. The bactericidal effect was evaluated by colony counts and scanning electron microscopy. The result of the colony counts showed a maximum 1.89 log reduction after irradiation at 2.1 W for 5 min. The temperature rise during aPDT/PACT was confirmed to be within a safe range. Furthermore, the light energy transmittance through the root was at a peak approximately 1 min after the start of irradiation, indicating that most of the ICG in the root canal was consumed. This study shows that aPDT/PACT can suppress E. faecalis in infected root canals with high efficiency.