Phototargeting human periodontal pathogens in vivo

The influence of growth medium on the photodynamic susceptibility of Aggregatibacter actinomycetemcomitans to antimicrobial blue light

The aim of this study was to investigate whether antimicrobial blue light (aBL) can cause the death of Aggregatibacter actinomycetemcomitans (A.a) and to determine the influence of different culture media, specifically brain heart infusion and blood agar, on bacterial survival fraction. An LED emitting at 403 ± 15 nm, with a radiant power of 1W, irradiance of 588.2 mW/cm2, and an irradiation time of 0 min, 1 min, 5 min, 10 min, 30 min, and 60 min, was used. The plates were incubated in microaerophilic conditions at 37 °C for 48 h, and the colony-forming units were counted. The photosensitizers were investigated using spectroscopy and fluorescence microscopy. There was no significant difference between the culture media (p > 0.05). However, a statistical reduction in both media was observed at 30 min (1058 J/cm2) (p < 0.05). The findings of this study suggest that aBL has the potential to kill bacteria regardless of the culture media used. Light therapy could be a promising and cost-effective strategy for preventing periodontal disease when used in combination with mechanical plaque control.

Photoinactivation and Photoablation of Porphyromonas gingivalis

Several types of phototherapy target human pathogens and Porphyromonas gingivitis (Pg) in particular. The various approaches can be organized into five different treatment modes sorted by different power densities, interaction times, effective wavelengths and mechanisms of action. Mode 1: antimicrobial ultraviolet (aUV); mode 2: antimicrobial blue light (aBL); mode 3: antimicrobial selective photothermolysis (aSP); mode 4: antimicrobial vaporization; mode 5: antimicrobial photodynamic therapy (aPDT). This report reviews the literature to identify for each mode (a) the putative molecular mechanism of action; (b) the effective wavelength range and penetration depth; (c) selectivity; (d) in vitro outcomes; and (e) clinical trial/study outcomes as these elements apply to Porphyromonas gingivalis (Pg). The characteristics of each mode influence how each is translated into the clinic.

The Parameters Affecting Antimicrobial Efficiency of Antimicrobial Blue Light Therapy: A Review and Prospect

Antimicrobial blue light (aBL) therapy is a novel non-antibiotic antimicrobial approach which works by generating reactive oxygen species. It has shown excellent antimicrobial ability to various microbial pathogens in many studies. However, due to the variability of aBL parameters (e.g., wavelength, dose), there are differences in the antimicrobial effect across different studies, which makes it difficult to form treatment plans for clinical and industrial application. In this review, we summarize research on aBL from the last six years to provide suggestions for clinical and industrial settings. Furthermore, we discuss the damage mechanism and protection mechanism of aBL therapy, and provide a prospect about valuable research fields related to aBL therapy.

Response of genes related to iron and porphyrin transport in Porphyromonas gingivalis to blue light

BACKGROUND

Antimicrobial blue light (aBL) kills a variety of bacteria, including Porphyromonas gingivalis. However, little is known about the transcriptomic response of P. gingivalis to aBL therapy. This study was designed to evaluate the selective cytotoxicity of aBL against P. gingivalis over human cells and to further investigate the genetic response of P. gingivalis to aBL at the transcriptome level.

METHODS

Colony forming unit (CFU) testing, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM) were used to investigate the antimicrobial effectiveness of blue light against P. gingivalis. The temperatures of the irradiated targets were measured to prevent overheating. Multiple fluorescent probes were used to quantify reactive oxygen species (ROS) generation after blue-light irradiation. RNA sequencing (RNA-seq) was used to investigate the changes in global gene expression. Following the screening of target genes, real-time quantitative polymerase chain reaction (RT-qPCR) was performed to confirm the regulation of gene expression.

RESULTS

A 405 nm aBL at 100 mW/cm² significantly killed P. gingivalis within 5 min while sparing human gingival fibroblasts (HGFs). No obvious temperature changes were detected in the irradiated surface under our experimental conditions. RNA-seq showed that the transcription of multiple genes was regulated, and RT-qPCR revealed that the expression levels of the genes RgpA and RgpB, which may promote heme uptake, as well as the genes Ftn and FetB, which are related to iron homeostasis, were significantly upregulated. The expression levels of the FeoB-2 and HmuR genes, which are related to hydroxyl radical scavenging, were significantly downregulated.

CONCLUSIONS

aBL strengthens the heme uptake and iron export gene pathways while reducing the ROS scavenging pathways in P. gingivalis, thus improving the accumulation of endogenous photosensitizers and enhancing oxidative damage to P. gingivalis.

The effects of violet and blue light irradiation on ESKAPE pathogens and human cells in presence of cell culture media

Bacteria belonging to the group of ESKAPE pathogens are responsible for the majority of nosocomial infections. Due to the increase of antibiotic resistance, alternative treatment strategies are of high clinical relevance. In this context visible light as disinfection technique represents an interesting option as microbial pathogens can be inactivated without adjuvants. However cytotoxic effects of visible light on host cells have also been reported. We compared the cytotoxicity of violet and blue light irradiation on monocytic THP-1 and alveolar epithelium A549 cells with the inactivation effect on ESKAPE pathogens. THP-1 cells displayed a higher susceptibility to irradiation than A549 cells with first cytotoxic effects occurring at 300 J cm⁻² (405 nm) and 400 J cm⁻² (450 nm) in comparison to 300 J cm⁻² and 1000 J cm⁻², respectively. We could define conditions in which a significant reduction of colony forming units for all ESKAPE pathogens, except Enterococcus faecium, was achieved at 405 nm while avoiding cytotoxicity. Irradiation at 450 nm demonstrated a more variable effect which was species and medium dependent. In summary a significant reduction of viable bacteria could be achieved at subtoxic irradiation doses, supporting a potential use of visible light as an antimicrobial agent in clinical settings.

Evidence and Therapeutic Perspectives in the Relationship between the Oral Microbiome and Alzheimer's Disease: A Systematic Review

This review aims to clarify the nature of the link between Alzheimer’s disease and the oral microbiome on an epidemiological and pathophysiological level, as well as to highlight new therapeutic perspectives that contribute to the management of this disease. We performed a systematic review, following the Preferred Reporting Items for Systematic Reviews checklist, from January 2000 to July 2021. The terms “plaque,” “saliva,” and “mouth” were associated with the search term “oral diseases” and used in combination with the Boolean operator “AND”/“OR”. We included experimental or clinical studies and excluded conferences, abstracts, reviews, and editorials. A total of 27 articles were selected. Evidence for the impact of the oral microbiome on the pathophysiological and immunoinflammatory mechanisms of Alzheimer’s disease is accumulating. The impact of the oral microbiome on the development of AD opens the door to complementary therapies such as phototherapy and/or the use of prebiotic compounds and probiotic strains for global or targeted modulation of the oral microbiome in order to have a favourable influence on the evolution of this pathology in the future.

Cavity Disinfection With a 445 nm Diode Laser Within the Scope of Restorative Therapy - A Pilot Study

Introduction: Cavity disinfection is necessary to prevent a progressive infection of the crown dentin and pulp. Increasing intolerance and resistance to antiseptics and antibiotics as well as the controversy over the effects of those on the dental hard tissue and composite have prompted the investigation of alternative treatment options. The objective of this pilot study is to evaluate the antibacterial potential of a diode laser with a wavelength of 445 nm in the cavity preparation using the bacterium Streptococcus salivarius associated with caries in conjunction with the characteristics and influences of dentin on light transmission. Methods: The bactericidal effect of the laser irradiation was determined in culture experiments by using caries-free human dentin samples on bacteria-inoculated agar. For this, dentin discs (horizontally cut coronal dentin) of 500 µm and 1000 µm thicknesses were produced and irradiated with the laser with irradiation parameters of 0.7-1 W in a cw-mode and exposure times of between 5-30 s. Based on the different sample thicknesses, the penetration depth effect of the irradiation was ascertained after the subsequent incubation of the bacteria-inoculated agar. Additional influential parameters on the irradiation transmission were investigated, including surface moisture, tooth color as well as the presence of a smear layer on the dentin surface. Results: The optical transmission values of the laser radiation for dentin were significantly dependent on the sample thickness (P = 0.006) as well as its moisture content (P = 0.013) and were independent of the presence of a smear layer. There was a 40% reduction in bacteria after the radiography of the 500-µm-thick dentin samples, which was shown as the lowest laser dose (443 J/cm²). Conclusion: These findings indicate that the diode laser with light emission at a wavelength of 445 nm is interesting for the supportive cavity disinfection within the scope of caries therapy and show potential for clinical applications.

Light-based technologies for management of COVID-19 pandemic crisis

The global dissemination of the novel coronavirus disease (COVID-19) has accelerated the need for the implementation of effective antimicrobial strategies to target the causative agent SARS-CoV-2. Light-based technologies have a demonstrable broad range of activity over standard chemotherapeutic antimicrobials and conventional disinfectants, negligible emergence of resistance, and the capability to modulate the host immune response. This perspective article identifies the benefits, challenges, and pitfalls of repurposing light-based strategies to combat the emergence of COVID-19 pandemic.

Killing mechanism of bacteria within multi-species biofilm by blue light

Objectives: The aim of the study was to characterize the immediate and delayed effects of non-coherent blue-light treatment on the composition and viability of an in vitro biofilm composed of anaerobic multispecies, as well as the mechanisms involved. Methods: A multispecies biofilm was constructed of Streptococcus sanguinis, Actinomyces naeslundii, Porphyromonas gingivalis and Fusobacterium nucleatum, test groups were exposed to blue light. The multispecies biofilm was explored with a newly developed method based on flow cytometry and confocal microscopy. The involvement of the paracrine pathway in the phototoxic mechanism was investigated by a crossover of the supernatants between mono-species P. gingivalis and F. nucleatum biofilms. Results: Blue light led to a reduction of about 50% in the viable pathogenic bacteria P. gingivalis and F. nucleatum, vs that in the non-exposed biofilm. Biofilm thickness was also reduced by 50%. The phototoxic effect of blue light on mono-species biofilm was observed in P. gingivalis, whereas F. nucleatum biofilm was unaffected. A lethal effect was obtained when the supernatant of P. gingivalis biofilm previously exposed to blue light was added to the F. nucleatum biofilm. The effect was circumvented by the addition of reactive oxygen species (ROS) scavengers to the supernatant. Conclusion: Blue-light has an impact on the bacterial composition and viability of the multispecies biofilm. The phototoxic effect of blue light on P. gingivalis in biofilm was induced directly and on F. nucleatum via ROS mediators of the paracrine pathway. This phenomenon may lead to a novel approach for 'replacement therapy,' resulting in a less periodonto-pathogenic biofilm.

Antimicrobial Blue Light Inactivation of Polymicrobial Biofilms

Polymicrobial biofilms, in which mixed microbial species are present, play a significant role in persistent infections. Furthermore, polymicrobial biofilms promote antibiotic resistance by allowing interspecies transfer of antibiotic resistance genes. In the present study, we investigated the effectiveness of antimicrobial blue light (aBL; 405 nm), an innovative non-antibiotic approach, for the inactivation of polymicrobial biofilms. Dual-species biofilms with Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) as well as with P. aeruginosa and Candida albicans were reproducibly grown in 96-well microtiter plates or in the CDC biofilm reactor for 24 or 48 h. The effectiveness of aBL inactivation of polymicrobial biofilms was determined through colony forming assay and compared with that of monomicrobial biofilms of each species. aBL-induced morphological changes of biofilms were analyzed with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). For 24-h old monomicrobial biofilms formed in 96-well microtiter plates, 6.30-log₁₀ CFU inactivation of P. aeruginosa, 2.33-log₁₀ CFU inactivation of C. albicans and 3.48-log₁₀ CFU inactivation of MRSA were observed after an aBL exposure of 500 J/cm². Under the same aBL exposure, 6.34-log₁₀ CFU inactivation of P. aeruginosa and 3.11-log₁₀ CFU inactivation of C. albicans were observed, respectively, in dual-species biofilms. In addition, 2.37- and 3.40-log₁₀ CFU inactivation were obtained in MRSA and P. aeruginosa, dual-species biofilms. The same aBL treatment of the biofilms developed in the CDC-biofilm reactor for 48 h significantly decreased the viability of P. aeruginosa monomicrobial and polymicrobial biofilm when cocultured with MRSA (3.70- and 3.56-log₁₀ CFU inactivation, respectively). 2.58-log₁₀ CFU inactivation and 0.86-log₁₀ CFU inactivation was detected in MRSA monomicrobial and polymicrobial biofilm when cocultured with P. aeruginosa. These findings were further supported by the CLSM and SEM experiments. Phototoxicity studies revealed a no statistically significant loss of viability in human keratinocytes after an exposure to 216 J/cm² and a statistically significant loss of viability after 500 J/cm². aBL is potentially an alternative treatment against polymicrobial biofilm-related infections. Future studies will aim to improve the efficacy of aBL and to investigate aBL treatment of polymicrobial biofilm-related infections in vivo.

Efficacy of an LED toothbrush on a Porphyromonas gingivalis biofilm on a sandblasted and acid-etched titanium surface: an in vitro study

Purpose

The aim of this study was to evaluate the antimicrobial effect of a newly devised toothbrush with light-emitting diodes (LEDs) on Porphyromonas gingivalis attached to sandblasted and acid-etched titanium surfaces.

Methods

The study included a control group, a commercial photodynamic therapy (PDT) group, and 3 test groups (B, BL, and BLE). The disks in the PDT group were placed in methylene blue and then irradiated with a diode laser. The B disks were only brushed, the BL disks were brushed with an LED toothbrush, and the BLE disks were placed into erythrosine and then brushed with an LED toothbrush. After the different treatments, bacteria were detached from the disks and spread on selective agar. The number of viable bacteria and percentage of bacterial reduction were determined from colony counts. Scanning electron microscopy was performed to visualize bacterial alterations.

Results

The number of viable bacteria in the BLE group was significantly lower than that in the other groups (P<0.05). Scanning electron microscopy showed that bacterial cell walls were intact in the control and B groups, but changed after commercial PDT and LED exposure.

Conclusions

The findings suggest that an LED toothbrush with erythrosine treatment was more effective than a commercial PDT kit in reducing the number of P. gingivalis cells attached to surface-modified titanium in vitro.

Remediation of adult black dental stains by phototherapy

Introduction and aims

This study investigates the effects of the application of antimicrobial phototherapy on black-stained tooth surfaces. Key variables were area, color and time taken to reappearance of black stain following dental prophylaxis with and without antimicrobial phototherapy. Differences in bacterial composition of black stain (specifically Aggregatibacter actinomycetemcomitans, Tannerella forsythia, and Porphyromonas gingivalis) were analyzed.

Material and methods

The phototherapy device used was GLO™ Science LLC, New York, America, emitting light at 475 nm and a power of 3 W. Light was applied in 2 cycles of 8 min on 31 volunteers. Microbial identification was carried out on DNA extracted from black plaque. This study is registered with ClinicalTrials.gov, number NCT03309748.

Results

Following antimicrobial phototherapy, 64.5% of patients displayed reduced pigmentation area. Plaque color was lighter in 48.4% of subjects. Pigmentation area and depth of color returned to normal levels during the course of the study. Colonization by the three bacterial species decreased, although the changes were not statistically significant. We report a key novel finding showing elevated levels of colonization by Tannerella forsythia (83.9%) in adult black stain.

Conclusions

Application of phototherapy results in a reduction in area, color and bacterial colonization of black plaque in adults. The changes were not found to be statistically significant, perhaps owing to the low illumination power of the home-whitening device. For the first time, we document the elevated presence of Tannerella forsythia in adult black stain. We also demonstrate the potential application of a commercially available home-whitening device for black plaque treatment.

Recent Patents on Light-Based Anti-Infective Approaches

BACKGROUND

Antibiotic resistance is one of the most serious health threats to modern medicine. The lack of potent antibiotics puts us at a disadvantage in the fight against infectious diseases, especially those caused by antibiotic-resistant microbial strains. To this end, an urgent need to search for alternative antimicrobial approaches has arisen. In the last decade, light-based anti-infective therapy has made significant strides in this fight to combat antibiotic resistance among various microbial strains. This method includes utilizing antimicrobial blue light, antimicrobial photodynamic therapy, and germicidal ultraviolet irradiation, among others. Light-based therapy is advantageous over traditional antibiotics in that it eradicates microbial cells rapidly and the likelihood of light-resistance development by microbes is low.

METHODS

This review highlights the patents on light-based therapy that were filed approximately within the last decade and are dedicated to eradicating pathogenic microorganisms. The primary database that was used for the search was Google Patents. The searches were performed using the keywords including blue light, antimicrobial photodynamic therapy, ultraviolet irradiation, antibiotic resistance, disinfection, bacterium, fungus, and virus.

RESULTS

Forty-five patents were obtained in our search: 9 patents for the antimicrobial blue light approach, 21 for antimicrobial photodynamic therapy, 11 for UV irradiation, and lastly 4 for other light-based anti-infective approaches. The treatments and devices discussed in this review are interestingly enough able to be used in various different functions and settings, such as dental applications, certain eye diseases, skin and hard surface cleansing, decontamination of internal organs (e.g., the stomach), decontamination of apparel and equipment, eradication of pathogenic microorganisms from buildings and rooms, etc. Most of the devices and inventions introduce methods of destroying pathogenic bacteria and fungi without harming human cells and tissues.

CONCLUSIONS

Light-based antimicrobial approaches hold great promise for the future in regards to treating antibiotic-resistant infections and related diseases.

Antimicrobial blue light inactivation of pathogenic microbes: State of the art

As an innovative non-antibiotic approach, antimicrobial blue light in the spectrum of 400-470nm has demonstrated its intrinsic antimicrobial properties resulting from the presence of endogenous photosensitizing chromophores in pathogenic microbes and, subsequently, its promise as a counteracter of antibiotic resistance. Since we published our last review of antimicrobial blue light in 2012, there have been a substantial number of new studies reported in this area. Here we provide an updated overview of the findings from the new studies over the past 5 years, including the efficacy of antimicrobial blue light inactivation of different microbes, its mechanism of action, synergism of antimicrobial blue light with other angents, its effect on host cells and tissues, the potential development of resistance to antimicrobial blue light by microbes, and a novel interstitial delivery approach of antimicrobial blue light. The potential new applications of antimicrobial blue light are also discussed.

Gut Microbiota and Salivary Diagnostics: The Mouth Is Salivating to Tell Us Something

The microbiome of the human body represents a symbiosis of microbial networks spanning multiple organ systems. Bacteria predominantly represent the diversity of human microbiota, but not to be forgotten are fungi, viruses, and protists. Mounting evidence points to the fact that the "microbial signature" is host-specific and relatively stable over time. As our understanding of the human microbiome and its relationship to the health of the host increases, it is becoming clear that many and perhaps most chronic conditions have a microbial involvement. The oral and gastrointestinal tract microbiome constitutes the bulk of the overall human microbial load, and thus presents unique opportunities for advancing human health prognosis, diagnosis, and therapy development. This review is an attempt to catalog a broad diversity of recent evidence and focus it toward opportunities for prevention and treatment of debilitating illnesses.

Impact of Docosahexaenoic Acid Therapy on Subgingival Plaque Microbiota

BACKGROUND

Oral docosahexaenoic acid (DHA) + aspirin therapy has been shown to reduce periodontal probing depth (PD) and local inflammatory mediators in gingival crevicular fluid (GCF) among patients with untreated chronic periodontal disease. Whether DHA + aspirin therapy influences specific bacterial burden in this setting is unknown. Thus, the aim of this study is to evaluate the impact of DHA with low-dose aspirin therapy on periodontal bacterial profile in patients with periodontitis.

METHODS

Fifty-five adults with moderate-to-severe periodontitis were enrolled in a randomized, 3-month double-masked, placebo-controlled trial of daily 2 g DHA or placebo capsules enriched with 81 mg aspirin; 46 enrollees completed the trial. In addition to clinical measurements and GCF sampling, subgingival plaque samples were collected from four posterior sites in all participants and analyzed by the checkerboard DNA-DNA hybridization technique. Presence of 40 periodontal bacterial species at baseline and 3 months was semiquantitatively estimated.

RESULTS

Despite broad improvements in clinical parameters, total bacteria and individual species counts in dental plaque did not differ significantly between baseline and 3 months in either group (P >0.1 for all). A modest effect of DHA + aspirin on Porphyromonas gingivalis counts was associated with 14% (95% confidence interval: 3% to 35%) of the observed benefit of DHA on PD. DHA + aspirin had no significant effect on individual plaque bacterial counts in unadjusted models or those adjusted for age, sex, and race (P >0.1 for all).

CONCLUSIONS

This pilot randomized, controlled trial suggests that DHA + aspirin therapy improves periodontitis largely by modulating host inflammatory response. Changes in individual species levels in subgingival plaque microbiota were not detectable; however, a small portion of the benefit appears to stem from changes in P. gingivalis levels in the DHA + aspirin treatment group. Whether this change in P. gingivalis levels leads to biofilm alteration with reversal of dysbiosis requires further longitudinal and more specific investigations.

The effect of blue light on periodontal biofilm growth in vitro

We have previously shown that blue light eliminates the black-pigmented oral bacteria Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, and Prevotella melaninogenica. In the present study, the in vitro photosensitivity of the above black-pigmented microorganisms and four Fusobacteria species (Fusobacterium nucleatum ss. nucleatum, F. nucleatum ss. vincentii, F. nucleatum ss. polymorphum, Fusobacterium periodonticum) was investigated in pure cultures and human dental plaque suspensions. We also tested the hypothesis that phototargeting the above eight key periodontopathogens in plaque-derived biofilms in vitro would control growth within the dental biofilm environment. Cultures of the eight bacteria were exposed to blue light at 455 nm with power density of 80 mW/cm2 and energy fluence of 4.8 J/cm2. High-performance liquid chromatography (HPLC) analysis of bacteria was performed to demonstrate the presence and amounts of porphyrin molecules within microorganisms. Suspensions of human dental plaque bacteria were also exposed once to blue light at 455 nm with power density of 50 mW/cm2 and energy fluence of 12 J/cm2. Microbial biofilms developed from the same plaque were exposed to 455 nm blue light at 50 mW/cm2 once daily for 4 min (12 J/cm2) over a period of 3 days (4 exposures) in order to investigate the cumulative action of phototherapy on the eight photosensitive pathogens as well as on biofilm growth. Bacterial growth was evaluated using the colony-forming unit (CFU) assay. The selective phototargeting of pathogens was studied using whole genomic probes in the checkerboard DNA-DNA format. In cultures, all eight species showed significant growth reduction (p < 0.05). HPLC demonstrated various porphyrin patterns and amounts of porphyrins in bacteria. Following phototherapy, the mean survival fractions were reduced by 28.5 and 48.2% in plaque suspensions and biofilms, respectively, (p < 0.05). DNA probe analysis showed significant reduction in relative abundances of the eight bacteria as a group in plaque suspensions and biofilms. The cumulative blue light treatment suppressed biofilm growth in vitro. This may introduce a new avenue of prophylactic treatment for periodontal diseases.