A new mechanism of action of fluoride on streptococci

Proteome Analysis of Oral Pathogens

The oral environment contains diverse communities of micro-organisms including bacteria, fungi, protozoa, and viruses. Studies of oral ecology have led to an appreciation of the complexity of the interactions that oral micro-organisms have with the host in both health and disease. Despite this, diseases such as dental caries and periodontal diseases are still worldwide human ailments, resulting in a high level of morbidity and an economic burden to society. Proteomics offers a new approach to the understanding of holistic changes occurring as oral micro-organisms adapt to environmental change within their habitats in the mouth.

Photodynamic potential of curcumin and blue LED against Streptococcus mutans in a planktonic culture

BACKGROUND

The photodynamic therapy (PDT) involves the use of light of specific wavelength to activate a nontoxic photosensitizing agent or dye in the presence of oxygen for eradication of target cells. In dentistry, this therapy is used to suppress the growth of microorganisms involved directly with dental decay and periodontitis process. There are evidences that curcumin dye is able to control microbial activity when illuminated with specific wavelength. The purpose of this study was to evaluate the in vitro efficacy of PDT using curcumin dye (Cur-C) in combination with a blue LED (L) device on a planktonic model of Streptococcus mutans (S. mutans).

METHODS

Suspensions (0.5 mL) containing S. mutans at 1×10(7)CFU mL(-1) were prepared and divided into 4 groups: Group C-L- (control: no treatment and 1 experimental condition), Group C+L- (curcumin at 3 different concentrations: 2000; 4000 and 8000 μM and 3 experimental conditions), Group C-L+ (LED at 3 different dosages: 24, 48 and 72 Jcm(-2) and 3 experimental conditions), and Group C+L+ (PDT group: curcumin at respective concentrations combined to LED dosages and 9 experimental conditions). Samples of each experimental condition were cultured in Petri dishes of BHI agar. Incubation in micro-aerophilia at 37°C for 48 h was performed for subsequent visual counting of CFU/mL. Data were transformed into log10 and analyzed by two-way ANOVA and Tukey's test at p<0.05.

RESULTS

Group C+L+, in specific experimental conditions, demonstrated a log bacterial reduction 70% higher than Group C-L-. Both groups C-L+ and C+L- presented a slight decrease in log bacterial counting.

CONCLUSION

This in vitro method was able to reduce the number of S. mutans in a planktonic suspension.

Evaluation of the effect of photoactivated disinfection with Radachlorin(®) against Streptococcus mutans (an in vitro study)

BACKGROUND

The use of photoactivated disinfection has had a significant medical and technological effect in bacterial inactivation, as an alternative to conventional antimicrobial methods. The main goal of this study was to investigate the effect of photoactivated disinfection on Streptococcus mutans, when Radachlorin(®) was used as a photosensitizer.

METHODS

Streptococcus mutans samples of two different initial concentrations were treated with Radachlorin(®) gel (0.1%), irradiated by the light of a He-Ne laser (633nm), with energy density of 6J/cm(2), and cell viability was evaluated after culturing.

RESULTS

It was observed that the combination of Radachlorin(®) and laser was more effective than Radachlorin(®) or laser alone (p<0.05), in reduction of S. mutans and Radachlorin(®) was cytotoxic, in the dark, only for the lower concentration of bacteria. Lower concentration of S. mutans resulted in higher amount of killing, in the case of using Radachlorin(®) with or without laser.

CONCLUSIONS

The photoactivation of Radachlorin(®) using a He-Ne laser could inactivate S. mutans to a significant level. In addition Radachlorin(®) might be cytotoxic in the dark, for the lower concentration of bacteria.

Interaction between GIC and S. sanguis biofilms: Antibacterial properties and changes of surface hardness

OBJECTIVE

The aim of this study was to investigate the interaction of Streptococcus sanguis with two glass-ionomer formulations (GIC:A containing fluoride and GIC:B without fluoride) with particular reference to bacterial growth and changes in hardness of the cement with respect to time.

MATERIALS AND METHODS

Discs of two water activated glass-ionomer cements were prepared according to the manufacturer's instruction. Hydroxyapatite discs (HA) were used as controls. 3D laser scanning technique was used to characterize surface roughness and area of the substrate prior to growing biofilms. Surface hardness was evaluated before and after biofilm growth. A constant depth film fermenter system (CDFF) was used to grow S. sanguis biofilms on the specimens in a similar manner to that described previously by Wilson et al. in 1995. For susceptibility measurement, specimens were removed from CDFF aseptically over periods up to 14d after the first colonization with bacteria. Counts of viable bacterial in the accumulating biofilm layer on each surface were measured and converted to colony forming units per unit surface area. To determine the effect of storage media, hardness discs were exposed to distilled water, lactic acid pH 4, lactic acid pH 5, citric acid pH 5, artificial saliva and S. sanguis biofilms. Twenty-four hours after preparing and subsequent autoclaving, specimens were transferred to a vessel containing 40 ml storage medium. The specimens were investigated for periods up to 7d.

RESULTS

The viable counts of S. sanguis per mm2 on GIC:A were significantly less than those on HA and GIC:B during the first 5d (p<0.05). The viable counts of bacteria on the surface of GIC:B were lower during the initial 5d when compared to HA. Exposure of GIC:A and GIC:B to different medium produced softening to the surface of cement. It is apparent that the effects of the biofilms are significantly greater than storage in water but similar to storage in lactic acid pH 5.

CONCLUSIONS

This investigation showed that the growth of S. sanguis biofilms were significantly affected by both glass-ionomer formulations, the greater reduction being noted on the surface of the fluoride containing GIC. S. sanguis biofilms produced reduction on the surface hardness of the cement equivalent to that seen after immersion in lactic acid at pH 5. This indicates that while S. sanguis biofilm is affected by the GIC, there is also a decrease in hardness of the cement indicating some cement degradation.

Co-operative inhibition by fluoride and zinc of glucosyl transferase production and polysaccharide synthesis by mutans streptococci in suspension cultures and biofilms

Fluoride and zinc, alone or in combination at concentrations of 0.2 mM, inhibited production-secretion of glucosyltranferases by Streptococcus mutans UA159 growing in suspension cultures. Inhibition did not involve growth inhibition or starvation. Fluoride and zinc also inhibited glucan production, especially insoluble glucan, in fed-batch biofilms. Inhibition of biofilms appeared to be associated with starvation as indicated by markedly decreased ATP pools and iodophilic polysaccharide levels in biofilm cells. As insoluble glucans are important for virulence of mutans streptococci, the inhibitory actions of fluoride and zinc could significantly affect cariogenicity.

Influence of a Fluoride Mouthrinse on Mutans Streptococci in Schoolchildren

This study aimed to determine whether the long-term use of a fluoride mouthrinse affects the salivary levels of mutans streptococci. Two hundred and fifteen schoolchildren (aged 9-10 years) participated. One hundred and forty-nine of these children had used a fluoride mouthrinse since 5 years of age at nursery school, and the remaining 66 children had not. DFT (decayed and filled teeth) was recorded, and the salivary levels of Streptococcus mutans and Streptococcus sobrinus were measured using mitis salivarius bacitracin agar. The group that had used a fluoride mouthrinse had a significantly lower prevalence of both S. mutans and S. sobrinus (p = 0.038) and a significantly lower DFT score (p < 0.001) than the other group. Using logistic regression analysis including caries experience at baseline as a dependent variable, the odds ratio of carrying S. mutans alone was 8.0 (p = 0.066) and that of carrying both S. mutans and S. sobrinus was 16.5 (p = 0.022) in the group that had not used the fluoride mouthrinse. Children carrying both S. mutans and S. sobrinus had a higher caries incidence in 1 year than the others, with odds ratios of 5.73 (p = 0.067) in the group with a fluoride mouthrinse and 3.47 (p = 0.035) in the group without it. These results show that the long-term use of a fluoride mouthrinse is associated with reduced salivary levels of mutans streptococci and this bacterial reduction may partly contribute to the suppression of dental caries in children using a long-term fluoride mouthrinse.

Use of hand held photopolymerizer to photoinactivate Streptococcus mutans

OBJECTIVES

The main focus of this research was to investigate the photodynamic therapy (PDT), in vitro, acting on Streptococcus mutans and fibroblasts. A hand held photopolymerizer (HHP) and a classical photosensitizer (Rose Bengal) were used to induce photodynamic response.

METHODS

S. mutans and fibroblast were treated with different concentrations of Rose Bengal (0-50 microM) irradiated with light (400-500 nm) for different time periods (0-40s) and then cell viability was evaluated.

RESULTS

It was observed that the light (per se) is not toxic and in the dark Rose Bengal is toxic to the cells tested only at concentrations above 2.5 microM. Under light exposure concentrations of Rose Bengal above 0.5 microM all S. mutans were killed with no cytotoxic effects to fibroblasts.

CONCLUSIONS

For the purpose of this work, the photoactivation of Rose Bengal, using the HHP, inactivated the bacteria without affecting the fibroblast viability.

Use of visible light-based photodynamic therapy to bacterial photoinactivation

The main focus of this laboratory exercise was to investigate the photodynamic therapy (PDT) acting over Streptococcus mutans. A handheld photopolymerizer and a classical photosensitizer (Rose Bengal) were used to induce photodynamic response. In this way, a suspension of S. mutans was treated with different concentrations of Rose Bengal (0-10 μmol/liter), irradiated with a light (400-600 nm) for 20 s, and then cell viability was evaluated. It was observed that the light (per se) is not toxic, and in the dark, Rose Bengal is toxic only to the cells tested at concentrations above 5.0 μmol/liter. Under light exposure, concentrations of Rose Bengal above 0.5 μmol/liter killed all S. mutans. Therefore, for the purpose of our work, the photoactivation of Rose Bengal using the handheld photopolymerizer was efficient in bacteria inactivation.

Physiological (osmotic fragility) and morphological effects on red blood cells: action of phytic acid and stannous fluoride

Phytic acid occurs in foods derived from plants. We have investigated the possibility that phytic acid and stannous fluoride are capable of altering the physiological properties (osmotic fragility) and morphological properties of red blood cells (RBC). Osmotic fragility was unchanged by the presence of phytic acid and stannous fluoride in the studied concentrations, but RBC morphology was modified in the presence of the studied substances. In conclusion, the alterations to RBC morphology were not sufficient to promote modifications in osmotic fragility. Our results suggest that the chelating properties of phytic acid could be responsible for the observed effects.Key words: phytic acid, stannous fluoride, morphology, osmotic fragility.

The effect of carbon source and fluoride concentrations in the streptococcus mutans biofilm formation*

The main objective of this class experiment is to show the influence of carbon source and of different fluoride concentrations on the biofilm formation by the bacterium Streptococcus mutans. The observation of different biofilm morphology as a function of carbon source and fluoride concentration allows an interesting discussion regarding the metabolic pathways that lead to cavity development, about the role of fluoride on this disease prevention, and also on the importance of biofilm formation to the cariogenic potential of this bacterium, one of the main responsible for this multifatorial disease appearance. On addition to that, the low execution cost and the simple technical apparatus makes this experiment easy to perform.

Fluoride and organic weak acids as modulators of microbial physiology

Fluoride is widely used as an anticaries agent in drinking water and a variety of other vehicles. This use has resulted in major health benefits. However, there are still open questions regarding the mechanisms of anticaries action and the importance of antimicrobial effects in caries reduction. Fluoride acts in multiple ways to affect the metabolism of cariogenic and other bacteria in the mouth. F(-)/HF can bind directly to many enzymes, for example, heme-containing enzymes or other metalloenzymes, to modulate metabolism. Fluoride is able also to form complexes with metals such as aluminum or beryllium, and the complexes, notably AlF(4)(-) and BeF(3)(-).H(2)O, can mimic phosphate with either positive or negative effects on a variety of enzymes and regulatory phosphatases. The fluoride action that appears to be most important for glycolytic inhibition at low pH in dental plaque bacteria derives from its weak-acid properties (pK(a)=3.15) and the capacity of HF to act as a transmembrane proton conductor. Since many of the actions of fluoride are related to its weak-acid character, it is reasonable to compare fluoride action to those of organic weak acids, including metabolic acids, food preservatives, non-steroidal anti-inflammatory agents and fatty acids, all of which act to de-energize the cell membrane by discharging DeltapH. Moreover, with the realization that the biofilm state is the common lifestyle for most microorganisms in nature, there is need to consider interactions of fluoride and organic weak acids with biofilm communities. Hopefully, this review will stimulate interest in the antimicrobial effects of fluoride or other weak acids and lead to more effective use of the agents for disease control and other applications.

Fluoride modifies adhesion of Streptococcus pyogenes

Streptococcus pyogenes grown in the presence of subinhibitory concentrations of sodium fluoride had a diminished ability, compared to control cells, to adhere to buccal cells, collagen, fibronectin, and laminin. In addition, sodium fluoride was a competitive inhibitor of streptococcal adhesion to collagen and fibronectin, but not laminin. It is suggested that sodium fluoride may be useful in therapy or prophylaxis in infections involving group A streptococci.

Modulation of glucan-binding protein activity in streptococci by fluoride

Glucan-binding lectin (GBL) activity of Streptococcus sobrinus was significantly reduced by fluoride in the growth medium. Approximately 1.5 mM fluoride was required for a 50% reduction in GBL activity. In addition to the GBL, several other glucan-binding proteins were reduced when the bacteria were grown in subinhibitory fluoride. Fluoride had no effect on glucosyltransferases (GTFs), enzymes capable of converting sucrose into alpha-1,6-glucans. All the proteins were detected by use of enhanced chemiluminescence (ECL of fluorescein-labeled dextran) and Western blotting of renatured SDS-PAGE gels. The effects of fluoride on the bacteria were abrogated when the manganous ion was included in the growth medium. It thus appears that one mechanism of action of fluoridated water is its effects on glucan-binding proteins. The fluoride may be reducing metabolism of the mangano aquo ion, essential for expression of the glucan-binding proteins.