Streptococcus mutans photoinactivation using a combination of a high potency photopolymerizer and rose bengal

Morphological changes and viability of Streptococcus mutans biofilm treated with erythrosine: A confocal laser scanning microscopy analysis

Antimicrobial photodynamic therapy (a-PDT) is a modality that aims to induce microorganisms through visible light, a photosensitizer, and molecular oxygen. This therapy has shown promising results in controlling cariogenic biofilm in vitro and in vivo counterparts. This study investigated bacterial viability and morphological characterization of Streptococcus mutans mature biofilms after combination of erythrosine and a high potency dental curing light. Biofilms were formed on saliva-coated hydroxyapatite disks in batch culture. The samples were performed in triplicates. Fresh medium was replaced daily for five days and treated using 40 μM of E activated by HL 288 J/cm2 and total dose of 226 J at 1200 mW/cm2. Phosphate buffer saline and 0.12% of chlorhexidine were used as negative and positive control, respectively. After treatment, biofilms were assessed for microbial viability and morphological characterization by means of bio-volume and thickness. COMSTAT software was used for image analysis. Data were analyzed using two-way ANOVA followed by Tukey test with significance level 5%. The application of a-PDT and CHX treatments decreased S. mutans bacterial viability. The image analysis showed more red cells on biofilms when compared to other groups, demonstrating photobacterial killing. Erythrosine irradiated with a high potency curing light can potentially act as an antimicrobial tool in the treatment of cariogenic biofilms. The morphology and viability of microorganisms were impacted after treatment. Treatment with photodynamic therapy may be able to reduce the bio-volume and viability of bacteria present in biofilms. CLINICAL RELEVANCE AND RESEARCH HIGHLIGHTS: The use of the a-PDT technique has been applied in dentistry with satisfactory results. Some applications of this technique are in stomatology and endodontics. In the present study, we sought to understand the use of photodynamic therapy in the control of biofilm and the results found are compatible with the objective of microbiological control proposed by this technique, thus raising the alert for future studies in vivo using the combination of a-PDT with erythrosine, since they are easily accessible materials for the dental surgeon and can be applied in clinical practice.

Rose bengal-mediated photodynamic inactivation against periodontopathogens in vitro

BACKGROUND

The main goal of periodontal therapy is to eliminate the spread of infection in the periodontium. Antimicrobial photodynamic therapy (aPDT) is a bactericidal method that has been recently introduced for controlling periodontal infection. The aim of this in vitro study was to evaluate the effect of aPDT using a combination of medium-power blue light-emitting diodes (LEDs) and rose bengal (RB) on selected key periodontopathogens.

METHODS

Porphyromonas gingivalis ATCC33277, Aggregatibacter actinomycetemcomitans ATCC29523 and Fusobacterium nucleatum ATCC10953 were used in the experiments. Each bacterial suspension was irradiated with a blue LED (BL) (450-470 nm, output power density of 1.2 W/cm²) for 20-60 s (6-18 J/cm²), treated with RB (1 min), or subjected to a combination of RB treatment and BL irradiation (40 s, 12 J/cm²). All bacterial suspensions were serially diluted, plated and incubated anaerobically or microaerobically, and the numbers of colony-forming units (CFUs) were counted on day 7. One-way analysis of variance (ANOVA) and Tukey's HSD tests were used for statistical analysis.

RESULTS

Treatment with BL irradiation from 6 to 18 J/cm² did not significantly reduce the number of CFUs, whereas treatment with RB alone induced a low-to-high reduction in the bacterial CFUs in a dye concentration-dependent manner. Furthermore, the difference in the effects obtained with 16 μg/mL and 160 μg/mL RB was not statistically significant. Treatment with the BL at 12 J/cm² combined with 160 μg/mL RB yielded maximal log reductions of 3.03, 4.2 and 2.23 in P. gingivalis, A. actinomycetemcomitans and F. nucleatum CFUs, respectively.

CONCLUSION

Within the limits of this study, the three periodontal pathogens, especially A. actinomycetemcomitans, were susceptible to photodynamic inactivation by the combination of the BL and RB. RB-mediated aPDT may offer a viable alternative tool for periodontal pathogen treatment, especially for A. actinomycetemcomitans eradication. aPDT may be a valuable tool for the treatment of periodontal diseases, particularly those in which A. actinomycetemcomitans is a dominating pathogen.

Photodynamic optimization by combination of xanthene dyes on different forms of Streptococcus mutans: An in vitro study

OBJECTIVE

The photokilling rate in antimicrobial photodynamic therapy (a-PDT) is highly related to interaction of reactive oxygen species (ROS) produced, ability of photosensitizers (PS) in incorporating into microorgansims and light devices/microorganism type. Since xanthene dyes (Rose Bengal and Erythrosine) are present in the dental practice as PS, have high quantum yield of singlet oxygen and are efficiently incorporated into bacterial cells, the additive bactericidal ability of a combination of xanthene dyes was tested on planktonic cultures and biofilms of Streptococcus mutans when irradiated by a hand-held LED photopolymerizer unit.

METHODS

Planktonic cultures of S. mutans (UA 159 ATCC 700610) were grown in BHI broth with 1 % sucrose. This culture was exposed to a concentrations of Rose Bengal (RB) and Erythrosine (ER) at 1.5, 3.5 μM, in combination (RB + ER + L+) / alone (RB + L+/ ER + L+) and irradiated with a blue LED high light intensity (L). Accordingly, concentrations of dyes and time irradiation were increased in 10 times and applied on 120 h - biofilms of S. mutans and compared with a 0.12 % Chlorhexidine solution (0.12 % - CHX). For statistical analysis, parametrical procedures were applied (n = 6; ANOVA test and Tukey post hoc test; α = 0.05) and data transformed into log ₁₀.

RESULTS

Substantial antimicrobial reduction was verified in planktonic cultures (∼ 7 log reduction) and biofilm (∼ 1 log reduction) for combined a-PDT group (RB + ER + L+) presenting a significant statistical difference to control group (p < 0.05) with similar effect to CHX group (p > 0.05).

CONCLUSION

Different forms of S. mutans can be effectively controlled by photodynamic therapy and optimized when in combination of xanthene dyes.

In vitro antimicrobial potential of infant mouthwashes against streptococcus mutans biofilm: A preliminary study

Background

Children and teenagers accumulate dental plaque easily due to immature motor coordination present at this specific age. Thus, chemical solutions such as mouthwashes are used for biofilm control. The widespread use of mouthwash could potentially change the oral environment though there is no evidence of its effects on the biofilm.

Aim

The present study aimed to investigate the in vitro antimicrobial potential of infant mouthwashes on mature Streptococcus mutans biofilm.

Methods

The susceptibility of S. mutans biofilm UA 159 (ATCC700610) to infant mouthwashes was tested with childrens mouthwashes containing the following active agents: G1-cetylpyridinium chloride, G2-xylitol and triclosan and G3-Malva sylvestris and xylitol. Phosphage-buffered saline (PBS) was used at the negative control (G4). In this study, cariogenic biofilm was exposed once a day for one minute to the mouthwashes over a period of five days. Following this, an aliquot of each mouthwash used was seeded in brain heart infusion (BHI) agar and then incubated at 37°C, 5% CO₂ for 48 h. The results were expressed as colony-forming units (CFU) and converted into log₁₀. The results were submitted to ANOVA and Tukey's test at 5%.

Results

It was observed 7.75, 7.66, and 7.49 CFU_log10 values to G1, G2, and G3, respectively, with 9.53 CFU_log10 value to G4. Accordingly, all studied mouthwashes showed no significant statistical difference between them but with statistically significant bacterial reduction in comparison to control group.

Conclusion

Infant mouthwashes presented a highly significant antimicrobial effect on cariogenic biofilm in an in vitro model, which raises concern when used by a young population.

Photodynamic inactivation as an emergent strategy against foodborne pathogenic bacteria in planktonic and sessile states

Foodborne microbial diseases are still considered a growing public health problem worldwide despite the global continuous efforts to ensure food safety. The traditional chemical and thermal-based procedures applied for microbial growth control in the food industry can change the food matrix and lead to antimicrobial resistance. Moreover, currently applied disinfectants have limited efficiency against biofilms. Therefore, antimicrobial photodynamic therapy (aPDT) has become a novel alternative for controlling foodborne pathogenic bacteria in both planktonic and sessile states. The use of aPDT in the food sector is attractive as it is less likely to cause antimicrobial resistance and it does not promote undesirable nutritional and sensory changes in the food matrix. In this review, aspects on the antimicrobial photodynamic technology applied against foodborne pathogenic bacteria and studied in recent years are presented. The application of photodynamic inactivation as an antibiofilm strategy is also reviewed.

Antimicrobial Photodynamic Inactivation Mediated by Rose Bengal and Erythrosine Is Effective in the Control of Food-Related Bacteria in Planktonic and Biofilm States

The thermal and chemical-based methods applied for microbial control in the food industry are not always environmentally friendly and may change the nutritional and organoleptic characteristics of the final products. Moreover, the efficacy of sanitizing agents may be reduced when microbial cells are enclosed in biofilms. The objective of this study was to investigate the effect of photodynamic inactivation, using two xanthene dyes (rose bengal and erythrosine) as photosensitizing agents and green LED as a light source, against Staphylococcus aureus, Listeria innocua, Enterococcus hirae and Escherichia coli in both planktonic and biofilm states. Both photosensitizing agents were able to control planktonic cells of all bacteria tested. The treatments altered the physicochemical properties of cells surface and also induced potassium leakage, indicating damage of cell membranes. Although higher concentrations of the photosensitizing agents (ranging from 0.01 to 50.0 μmol/L) were needed to be applied, the culturability of biofilm cells was reduced to undetectable levels. This finding was confirmed by the live/dead staining, where propidium iodide-labeled bacteria numbers reached up to 100%. The overall results demonstrated that photoinactivation by rose bengal and erythrosine may be a powerful candidate for the control of planktonic cells and biofilms in the food sector.