Inhibitory effect of carboxylated nanodiamond on oral pathogenic bacteria Streptococcus mutans.

BACKGROUND: Nanodiamonds (NDs) have been demonstrated to have bactericidal activity on several microorganisms and can be used in various kinds of dental materials. NDs are potential candidates for antibacterial dental materials. However, the possible inhibitory effect of NDs on oral pathogenic bacteria is largely unknown. This study was performed to investigate the inhibitory effects of carboxylated nanodiamond (cND) on Streptococcus mutans. METHODS: Fourier transform infrared spectroscopy was used to confirm carboxyl groups on the surface of commercial cND. The inhibitory effect of serially diluted cND on S. mutans was evaluated by spectrophotometry and plating methods. Escherichia coli was treated as a positive control in spectrophotometry. Chlorhexidine was used as a positive control in plating methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to confirm the antibacterial activity of cND. RESULTS: The results showed that cND exhibited a significant inhibitory effect on S. mutans. For S. mutans, the minimum inhibitory concentration was 4 µg/ml and the minimum bactericidal concentration was 16 µg/ml. SEM and TEM results indicated that cND functioned as an antibacterial agent, likely due to its ability to disrupt the cell membrane of S. mutans. CONCLUSION: In conclusion, these findings demonstrated an inhibitory effect of cND on S. mutans and suggest its use as a potential antibacterial dental material.

Modification of cell wall polysaccharide guides cell division in Streptococcus mutans.

In ovoid-shaped, Gram-positive bacteria, MapZ guides FtsZ-ring positioning at cell equators. The cell wall of the ovococcus Streptococcus mutans contains peptidoglycan decorated with serotype c carbohydrates (SCCs). In the present study, we identify the major cell separation autolysin AtlA as an SCC-binding protein. AtlA binding to SCC is attenuated by the glycerol phosphate (GroP) modification. Using fluorescently labeled AtlA constructs, we mapped SCC distribution on the streptococcal surface, revealing enrichment of GroP-deficient immature SCCs at the cell poles and equators. The immature SCCs co-localize with MapZ at the equatorial rings throughout the cell cycle. In GroP-deficient mutants, AtlA is mislocalized, resulting in dysregulated cellular autolysis. These mutants display morphological abnormalities associated with MapZ mislocalization, leading to FtsZ-ring misplacement. Altogether, our data support a model in which maturation of a cell wall polysaccharide provides the molecular cues for the recruitment of cell division machinery, ensuring proper daughter cell separation and FtsZ-ring positioning.

Near Simultaneous Laser Scanning Confocal and Atomic Force Microscopy (Conpokal) on Live Cells.

Techniques available for micro- and nano-scale mechanical characterization have exploded in the last few decades. From further development of the scanning and transmission electron microscope, to the invention of atomic force microscopy, and advances in fluorescent imaging, there have been substantial gains in technologies that enable the study of small materials. Conpokal is a portmanteau that combines confocal microscopy with atomic force microscopy (AFM), where a probe "pokes" the surface. Although each technique is extremely effective for the qualitative and/or quantitative image collection on their own, Conpokal provides the capability to test with blended fluorescence imaging and mechanical characterization. Designed for near simultaneous confocal imaging and atomic force probing, Conpokal facilitates experimentation on live microbiological samples. The added insight from paired instrumentation provides co-localization of measured mechanical properties (e.g., elastic modulus, adhesion, surface roughness) by AFM with subcellular components or activity observable through confocal microscopy. This work provides a step by step protocol for the operation of laser scanning confocal and atomic force microscopy, simultaneously, to achieve same cell, same region, confocal imaging, and mechanical characterization.

La actividad antibacteriana de Camellia sinensis comparada con propóleo frente al Streptococcus mutans / Antibacterial activity of Camellia sinensis versus propolis against Streptococcus mutans

RESUMEN Introducción: El té verde (Camellia sinensis) y el propóleo presentan flavonoides, que inhiben el crecimiento, metabolismo y la coagregación del Streptococcus mutans, principal agente causal de la caries dental. Objetivo: Evaluar la actividad antibacteriana in vitro del extracto etanólico del té verde (Camellia sinensis) al 10 por ciento y 20 por ciento comparado con extracto etanólico de propóleo al 10 por ciento y 20 por ciento, frente al crecimiento de cepas de Streptococcus mutans (ATCC 25175). Métodos: Estudio experimental in vitro, longitudinal, prospectivo y comparativo. El universo estuvo constituido por 90 discos de difusión y la muestra por 15 discos embebidos en té verde (Camellia sinensis) o propóleo a diferentes concentraciones, clorhexidina acuosa al 0,12 por ciento y agua destilada. El tamaño de muestra se calculó por fórmula de comparación de medias, después de realizar un estudio piloto. Se colocaron los discos de difusión embebidos en las sustancias sobre agar Mueller Hinton, sembrado con Streptococcus mutans (ATCC 25175), haciendo medición del ancho de los halos inhibitorios a las 24 y 48 h. Se aplicaron pruebas de comparación no paramétricas de Kruskal Wallis y la prueba rangos de Wilcoxon. Resultados: El máximo ancho de halo inhibitorio logrado por clorhexidina acuosa al 0,12 por ciento, extracto etanólico de té verde (Camellia sinensis) al 20 por ciento y extracto etanólico de propóleo al 20 por ciento fue a las 24 h con valores de 10,64 mm ± 0,924 mm, 6,82 mm ± 0,982 mm y 8,36 mm ± 1,286 mm, respectivamente. El extracto etanólico de té verde (Camellia sinensis) al 20 por ciento, presentó diferencias estadísticamente significativas respecto al extracto etanólico de propóleo al 20 por ciento, tanto a las 24 h (p= 0,013), como a las 48 h (p= 0,011). Conclusiones: Frente al crecimiento de cepas de Streptococcus mutans (ATCC 25175), el extracto etanólico de propóleo al 20 por ciento presenta mayor actividad antibacteriana respecto al extracto etanólico de té verde (Camellia sinensis) al 10 por ciento y 20 por ciento, actividad que disminuye con el paso del tiempo(AU)

ABSTRACT Introduction: Green tea (Camellia sinensis) and propolis contain flavonoids which inhibit the growth, metabolism and co-aggregation of Streptococcus mutans, the main causative agent of dental caries. Objective: Evaluate the antibacterial activity in vitro of 10 percent and 20 percent green tea (Camellia sinensis) ethanolic extract versus 10 percent and 20 percent propolis ethanolic extract against the growth of Streptococcus mutans (ATCC 25175) strains. Methods: An in vitro experimental prospective longitudinal comparative study was conducted. The study universe was 90 diffusion disks and the sample was 15 disks soaked up in green tea (Camellia sinensis) or propolis at various concentrations, 0.12 percent aqueous chlorhexidine and distilled water. Sample size was estimated by the comparison of means formula after conducting a pilot study. The diffusion disks soaked up in the substances were placed on Mueller Hinton agar planted with Streptococcus mutans (ATCC 25175) and the width of the inhibition haloes was measured at 24 h and 48 h. Nonparametric Kruskal-Wallis comparison tests and the Wilcoxon rank test were performed. Results: The maximum width of the inhibition halo achieved by 0.12 percent aqueous chlorhexidine, 20 percent green tea (Camellia sinensis) ethanolic extract, and 20 percent propolis ethanolic extract at 24 h was 10.64 mm ± 0.924 mm, 6.82 mm ± 0.982 mm and 8.36 mm ± 1.286 mm, respectively. The 20 percent green tea (Camellia sinensis) ethanolic extract showed statistically significant differences with respect to the 20 percent propolis ethanolic extract, both at 24 h (p= 0.013) and at 48 h (p= 0.011). Conclusions: The 20 percent propolis ethanolic extract displays greater antibacterial activity against the growth of Streptococcus mutans (ATCC 25175) strains than the 10 percent and 20 percent green tea (Camellia sinensis) ethanolic extract. This activity decreases with the passing of time(AU)

Efecto antibacteriano de una pasta dental con xilitol sobre Streptococcus mutans en saliva de gestantes / Antibacterial effect of a toothpaste with xylitol on Streptococcus mutans in pregnant women's saliva

RESUMEN Introducción: Durante la gestación, algunos cambios fisiológicos en la mujer propician un incremento de la placa dental y de la microbiota cariogénica. Esta condición unida a una modificación de la dieta y a una inadecuada higiene bucal condicionarían desfavorablemente la salud oral tanto de la madre como del bebé. Objetivo: Determinar el efecto antibacteriano de una pasta dental con xilitol sobre el recuento de Streptococcus mutans en saliva de gestantes. Métodos: Ensayo clínico, a doble ciego, que se realizó en el Centro de Salud "José Olaya" (Chiclayo Perú), en enero de 2017. Se trabajó con una población muestral de 50 gestantes en el segundo trimestre que cumplieron con los criterios establecidos. Se crearon dos grupos: 25 gestantes usaron dentífrico con 10 por ciento de xilitol y 25 gestantes usaron dentífrico sin xilitol. Se les tomó y proceso microbiológicamente una muestra de saliva antes del inicio del estudio y 14 días después del uso de las respectivas pastas. Se realizó el recuento de unidades formadoras de colonias de Streptococcus mutans en saliva con una confiabilidad altamente significativa mediante el coeficiente de correlación intraclase, calibración intra e interexaminador (1,000 y 0,999, respectivamente). El análisis de los datos se realizó mediante la prueba U de Mann-Whitney, considerando un nivel de significancia del 5 por ciento. Resultados: No se encontró diferencia significativa entre las gestantes que emplearon pasta dental con xilitol en comparación con las que utilizaron pasta dental sin xilitol (p= 0,062). Conclusiones: El efecto antibacteriano de la pasta dental comercial con xilitol es similar a una pasta dental sin xilitol sobre el recuento de Streptococcus mutans en saliva de gestantes(AU)

ABSTRACT Introduction: Some physiological changes occur in women during pregnancy which cause an increase in dental plaque and cariogenic microbiota. This situation, alongside a modification in the diet and inadequate oral hygiene, negatively affect the oral health of both the mother and the baby. Objective: Determine the antibacterial effect of a toothpaste with xylitol on the count of Streptococcus mutans in pregnant women's saliva. Methods: A double-blind clinical trial was conducted in José Olaya Health Center (Chiclayo, Peru) in January 2017. The sample population was 50 women in the second trimester of pregnancy who met the established inclusion criteria. Two groups were formed: 25 pregnant women used a toothpaste with 10 percent xylitol and the other 25 used a toothpaste without xylitol. A saliva sample was taken and processed microbiologically before the start of the study and 14 days after use of the two toothpastes. A count was performed of colony-forming units for Streptococcus mutans in saliva with highly significant reliability, using the intraclass correlation coefficient, and intra- and inter-rater calibration (1.000 and 0.999, respectively). Data analysis was based on the Mann-Whitney U Test, with a significance level of 5 percent. Results: No significant difference was found between the pregnant women who used the toothpaste with xylitol and those who used the toothpaste without xylitol (p= 0.062). Conclusions: The antibacterial effect of the commercial toothpaste with xylitol is similar to that of a toothpaste without xylitol in terms of the Streptococcus mutans count in pregnant women's saliva(AU)

Controllable acidophilic dual-emission fluorescent carbonized polymer dots for selective imaging of bacteria.

Fluorescent materials can be powerful contrast agents in photoelectric devices and for bioimaging. As emerging fluorescent materials, carbonized polymer dots (CPDs) with high quantum yields (QYs), long-wavelength emission and multiple functions are highly desired. Despite great progress in the synthetic methods and QYs of CPDs, multiple emission of CPDs is challenging. Therefore, we developed CPDs with dual-emission fluorescence in terms of inherent blue and red emission. In addition, CPDs with sole blue emission (B-CPDs) and red emission (R-CPDs) were synthesized, respectively, by regulating the reaction conditions to control the quantitative structure and emission centers. The absolute QY of R-CPDs in water was 24.33%. These three types of CPDs with dual/sole emission could be used in optoelectronic and bioimaging applications. With different CPDs coated on a commercially available gallium nitride light-emitting diode chip as a color-conversion layer, LEDs with blue, yellow, and red emission were achieved. Benefiting from the different emission intensities and emission peaks of R/B-CPDs in different pH conditions, they were used (without further modification) to distinguish between Porphyromonas gingivalis, Streptococcus mutans, Escherichia coli and Staphylococcus aureus in dental plaque biofilms (the first time this has been demonstrated). These findings could enable a new development direction of CPDs based on the design of multi-emission centers.

Effects of Nd:YAG laser irradiation on the growth of Candida albicans and Streptococcus mutans: in vitro study.

The purpose of this study was to evaluate the effects of Nd:YAG laser with flat-top handpiece on the in vitro growth of Candida albicans and Streptococcus mutans. The incidence of C. albicans (opportunistic commensal) and S. mutans (facultatively anaerobic) infections is increasing, despite available treatments. Cultures of Streptococcus mutans and Candida albicans were irradiated using Nd:YAG laser (LightWalker, Fotona) with flat-top handpiece (Genova, LightWalker, Fotona) at the following parameters: group G1: 0.25 W, 10 Hz, 15 s, 3 J and group G2: 1 W, 10 Hz, 60s, 59 J. The results were evaluated directly and 24 h after irradiation using a quantitative culture method (estimation of colony-forming units in 1 ml of suspension, cfu/ml), and microscopic analysis with Janus green stain and compared with control group in which laser was not applied. C. albicans was reduced by 20 up to 54% for G1, and for G2 by 10 up to 60% directly after the application. The cfu/ml values for S. mutans decreased by 13% (p = 0.1771) for G1 and 89% (p < 0.0001) for G2. In both test groups 24 h after the application, the number of colony-forming units decreased by 15-46% for G1 and by 15-64% for G2. The arrested cell division, increasing the surface area and increasing the number of metabolically inactive cells, were observed in morphometric analysis. Macroscopic and microscopic analyses revealed a reduction in cell number and a significant decrease of cell metabolism after laser application for both C. albicans and S. mutans.

The synthetic human beta-defensin-3 C15 peptide exhibits antimicrobial activity against Streptococcus mutans, both alone and in combination with dental disinfectants.

Streptococcus mutans is a major etiologic agent of human dental caries that forms biofilms on hard tissues in the human oral cavity, such as tooth and dentinal surfaces. Human ß-defensin-3 (HBD3) is a 45-amino-acid natural antimicrobial peptide that has broad spectrum antimicrobial activity against bacteria and fungi. A synthetic peptide consisting of the C-terminal 15 amino acids of HBD3 (HBD3-C15) was recently shown to be sufficient for its antimicrobial activity. Thus, clinical applications of this peptide have garnered attention. In this study, we investigated whether HBD3-C15 inhibits the growth of the representative cariogenic pathogen Streptococcus mutans and its biofilm formation. HBD3-C15 inhibited bacterial growth, exhibited bactericidal activity, and attenuated bacterial biofilm formation in a dose-dependent manner. HBD3-C15 potentiated the bactericidal and anti-biofilm activity of calcium hydroxide (CH) and chlorhexidine digluconate (CHX), which are representative disinfectants used in dental clinics, against S. mutans. Moreover, HBD3-C15 showed antimicrobial activity by inhibiting biofilm formation by S. mutans and other dentinophilic bacteria such as Enterococcus faecalis and Streptococcus gordonii, which are associated with dental caries and endodontic infection, on human dentin slices. These effects were observed for HBD3-C15 alone and for HBD3-C15 in combination with CH or CHX. Therefore, we suggest that HBD3-C15 is a potential alternative or additive disinfectant that can be used for the treatment of oral infectious diseases, including dental caries and endodontic infections.

Deficiency of RgpG Causes Major Defects in Cell Division and Biofilm Formation, and Deficiency of LytR-CpsA-Psr Family Proteins Leads to Accumulation of Cell Wall Antigens in Culture Medium by Streptococcus mutans.

Streptococcus mutans is known to possess rhamnose-glucose polysaccharide (RGP), a major cell wall antigen. S. mutans strains deficient in rgpG, encoding the first enzyme of the RGP biosynthesis pathway, were constructed by allelic exchange. The rgpG deficiency had no effect on growth rate but caused major defects in cell division and altered cell morphology. Unlike the coccoid wild type, the rgpG mutant existed primarily in chains of swollen, "squarish" dividing cells. Deficiency of rgpG also causes significant reduction in biofilm formation (P < 0.01). Double and triple mutants with deficiency in brpA and/or psr, genes coding for the LytR-CpsA-Psr family proteins BrpA and Psr, which were previously shown to play important roles in cell envelope biogenesis, were constructed using the rgpG mutant. There were no major differences in growth rates between the wild-type strain and the rgpG brpA and rgpG psr double mutants, but the growth rate of the rgpG brpA psr triple mutant was reduced drastically (P < 0.001). Under transmission electron microscopy, both double mutants resembled the rgpG mutant, while the triple mutant existed as giant cells with multiple asymmetric septa. When analyzed by immunoblotting, the rgpG mutant displayed major reductions in cell wall antigens compared to the wild type, while little or no signal was detected with the double and triple mutants and the brpA and psr single mutants. These results suggest that RgpG in S. mutans plays a critical role in cell division and biofilm formation and that BrpA and Psr may be responsible for attachment of cell wall antigens to the cell envelope.IMPORTANCEStreptococcus mutans, a major etiological agent of human dental caries, produces rhamnose-glucose polysaccharide (RGP) as the major cell wall antigen. This study provides direct evidence that deficiency of RgpG, the first enzyme of the RGP biosynthesis pathway, caused major defects in cell division and morphology and reduced biofilm formation by S. mutans, indicative of a significant role of RGP in cell division and biofilm formation in S. mutans These results are novel not only in S. mutans, but also other streptococci that produce RGP. This study also shows that the LytR-CpsA-Psr family proteins BrpA and Psr in S. mutans are involved in attachment of RGP and probably other cell wall glycopolymers to the peptidoglycan. In addition, the results also suggest that BrpA and Psr may play a direct role in cell division and biofilm formation in S. mutans This study reveals new potential targets to develop anticaries therapeutics.

Diverted Total Synthesis of Carolacton-Inspired Analogs Yields Three Distinct Phenotypes in Streptococcus mutans Biofilms.

The oral microbiome is a dynamic environment inhabited by both commensals and pathogens. Among these is Streptococcus mutans, the causative agent of dental caries, the most prevalent childhood disease. Carolacton has remarkably specific activity against S. mutans, causing acid-mediated cell death during biofilm formation; however, its complex structure limits its utility. Herein, we report the diverted total synthesis and biological evaluation of a rationally designed library of simplified analogs that unveiled three unique biofilm phenotypes further validating the role of natural product synthesis in the discovery of new biological phenomena.

The antimicrobial effects of the alginate oligomer OligoG CF-5/20 are independent of direct bacterial cell membrane disruption.

Concerns about acquisition of antibiotic resistance have led to increasing demand for new antimicrobial therapies. OligoG CF-5/20 is an alginate oligosaccharide previously shown to have antimicrobial and antibiotic potentiating activity. We investigated the structural modification of the bacterial cell wall by OligoG CF-5/20 and its effect on membrane permeability. Binding of OligoG CF-5/20 to the bacterial cell surface was demonstrated in Gram-negative bacteria. Permeability assays revealed that OligoG CF-5/20 had virtually no membrane-perturbing effects. Lipopolysaccharide (LPS) surface charge and aggregation were unaltered in the presence of OligoG CF-5/20. Small angle neutron scattering and circular dichroism spectroscopy showed no substantial change to the structure of LPS in the presence of OligoG CF-5/20, however, isothermal titration calorimetry demonstrated a weak calcium-mediated interaction. Metabolomic analysis confirmed no change in cellular metabolic response to a range of osmolytes when treated with OligoG CF-5/20. This data shows that, although weak interactions occur between LPS and OligoG CF-5/20 in the presence of calcium, the antimicrobial effects of OligoG CF-5/20 are not related to the induction of structural alterations in the LPS or cell permeability. These results suggest a novel mechanism of action that may avoid the common route in acquisition of resistance via LPS structural modification.

Bactericidal effect of the photocatalystic reaction of titanium dioxide using visible wavelengths on Streptococcus mutans biofilm.

BACKGROUND: The aim of this study was to determine the effect of titanium dioxide (TiO2) photocatalysis induced by the application of clinically acceptable visible light at 405nm on the growth of Streptococcus mutans biofilms. METHODS: S. mutans biofilms were grown on a hydroxyapatite (HA) disk and deposited in a rutile-type TiO2 solution at a concentration of 0.1mg/mL. TiO2 photocatalysis was measured for exposure to visible light (405nm) and ultraviolet (UV) light (254nm) produced by light-emitting diodes for 10, 20, 30, and 40min. After two treatments, the number of colonies formed in the final S. mutans biofilm on the HA disk were measured to confirm their viability, and the morphological changes of S. mutans were evaluated using scanning electronic microscopy. RESULTS: The bactericidal effects of 254- and 405-nm light resulted in > 5-log and 4-log reductions, respectively (p<0.05), after 20min of treatment and a>7-log reduction after 40min of treatment in both treatment groups relative to the control group. CONCLUSION: It was confirmed that the antibacterial effect could be shown by causing the photocatalytic reaction of TiO2 in S. mutans biofilm even at the wavelength of visible light (405nm) as at the wavelength of ultraviolet light (254nm).

Nicotine Enhances Interspecies Relationship between Streptococcus mutans and Candida albicans.

Streptococcus mutans and Candida albicans are common microorganisms in the human oral cavity. The synergistic relationship between these two species has been deeply explored in many studies. In the present study, the effect of alkaloid nicotine on the interspecies between S. mutans and C. albicans is explored. We developed a dual-species biofilm model and studied biofilm biomass, biofilm structure, synthesis of extracellular polysaccharides (EPS), and expression of glucosyltransferases (Gtfs). Biofilm formation and bacterial and fungal cell numbers in dual-species biofilms increased in the presence of nicotine. More C. albicans cells were present in the dual-species biofilms in the nicotine-treated groups as determined by scanning electron microscopy. The synthesis of EPS was increased by 1 mg/ml of nicotine as detected by confocal laser scanning microscopy. The result of qRT-PCR showed gtfs expression was upregulated when 1 mg/ml of nicotine was used. We speculate that nicotine promoted the growth of S. mutans, and more S. mutans cells attracted more C. albicans cells due to the interaction between two species. Since S. mutans and C. albicans are putative pathogens for dental caries, the enhancement of the synergistic relationship by nicotine may contribute to caries development in smokers.

Influence of Surface Properties on Adhesion Forces and Attachment of Streptococcus mutans to Zirconia In Vitro.

Zirconia is becoming a prevalent material in dentistry. However, any foreign bodies inserted may provide new niches for the bacteria in oral cavity. The object of this study was to explore the effect of surface properties including surface roughness and hydrophobicity on the adhesion and biofilm formation of Streptococcus mutans (S. mutans) to zirconia. Atomic force microscopy was employed to determine the zirconia surface morphology and the adhesion forces between the S. mutans and zirconia. The results showed that the surface roughness was nanoscale and significantly different among tested groups (P < 0.05): Coarse (23.94 ± 2.52 nm) > Medium (17.00 ± 3.81 nm) > Fine (11.89 ± 1.68 nm). The contact angles of the Coarse group were the highest, followed by the Medium and the Fine groups. Increasing the surface roughness and hydrophobicity resulted in an increase of adhesion forces and early attachment (2 h and 4 h) of S. mutans on the zirconia but no influence on the further development of biofilm (6 h~24 h). Our findings suggest that the surface roughness in nanoscale and hydrophobicity of zirconia had influence on the S. mutans initial adhesion force and early attachment instead of whole stages of biofilm formation.

Simultaneous spatiotemporal mapping of in situ pH and bacterial activity within an intact 3D microcolony structure.

Biofilms are comprised of bacterial-clusters (microcolonies) enmeshed in an extracellular matrix. Streptococcus mutans can produce exopolysaccharides (EPS)-matrix and assemble microcolonies with acidic microenvironments that can cause tooth-decay despite the surrounding neutral-pH found in oral cavity. How the matrix influences the pH and bacterial activity locally remains unclear. Here, we simultaneously analyzed in situ pH and gene expression within intact biofilms and measured the impact of damage to the surrounding EPS-matrix. The spatiotemporal changes of these properties were characterized at a single-microcolony level following incubation in neutral-pH buffer. The middle and bottom-regions as well as inner-section within the microcolony 3D structure were resistant to neutralization (vs. upper and peripheral-region), forming an acidic core. Concomitantly, we used a green fluorescent protein (GFP) reporter to monitor expression of the pH-responsive atpB (PatpB::gfp) by S. mutans within microcolonies. The atpB expression was induced in the acidic core, but sharply decreased at peripheral/upper microcolony regions, congruent with local pH microenvironment. Enzymatic digestion of the surrounding matrix resulted in nearly complete neutralization of microcolony interior and down-regulation of atpB. Altogether, our data reveal that biofilm matrix facilitates formation of an acidic core within microcolonies which in turn activates S. mutans acid-stress response, mediating both the local environment and bacterial activity in situ.

Singlet oxygen production by combining erythrosine and halogen light for photodynamic inactivation of Streptococcus mutans.

BACKGROUND: Photodynamic inactivation of microorganisms is based on a photosensitizing substance which, in the presence of light and molecular oxygen, produces singlet oxygen, a toxic agent to microorganisms and tumor cells. This study aimed to evaluate singlet oxygen quantum yield of erythrosine solutions illuminated with a halogen light source in comparison to a LED array (control), and the photodynamic effect of erythrosine dye in association with the halogen light source on Streptococcus mutans. METHODS: Singlet oxygen quantum yield of erythrosine solutions was quantified using uric acid as a chemical-probe in an aqueous solution. The in vitro effect of the photodynamic antimicrobial activity of erythrosine in association with the halogen photopolimerizing light on Streptococcus mutans (UA 159) was assessed during one minute. Bacterial cultures treated with erythrosine alone served as negative control. RESULTS: Singlet oxygen with 24% and 2.8% degradation of uric acid in one minute and a quantum yield of 0.59 and 0.63 was obtained for the erythrosine samples illuminated with the halogen light and the LED array, respectively. The bacterial cultures with erythrosine illuminated with the halogen light presented a decreased number of CFU mL(-1) in comparison with the negative control, with minimal inhibitory concentrations between 0.312 and 0.156mgmL(-1). CONCLUSIONS: The photodynamic response of erythrosine induced by the halogen light was capable of killing S. mutans. Clinical trials should be conducted to better ascertain the use of erythrosine in association with halogen light source for the treatment of dental caries.

Inactivation of glutamate racemase (MurI) eliminates virulence in Streptococcus mutans.

Inhibition of enzymes required for bacterial cell wall synthesis is often lethal or leads to virulence defects. Glutamate racemase (MurI), an essential enzyme in peptidoglycan biosynthesis, has been an attractive target for therapeutic interventions. Streptococcus mutans, one of the many etiological factors of dental caries, possesses a series of virulence factors associated with cariogenicity. However, little is known regarding the mechanism by which MurI influences pathogenesis of S. mutans. In this work, a stable mutant of S. mutans deficient in glutamate racemase (S. mutans FW1718) was constructed to investigate the impact of murI inactivation on cariogenic virulence in S. mutans UA159. Microscopy revealed that the murI mutant exhibited an enlarged cell size, longer cell chains, diminished cell⬜cell aggregation, and altered cell surface ultrastructure compared with the wild-type. Characterization of this mutant revealed that murI deficiency weakened acidogenicity, aciduricity, and biofilm formation ability of S. mutans (P<0.05). Real-time quantitative polymerase chain reaction (qRT-PCR) analysis demonstrated that the deletion of murI reduced the expression of the acidogenesis-related gene ldh by 44-fold (P<0.0001). The expression levels of the gene coding for surface protein antigen P (spaP) and the acid-tolerance related gene (atpD) were down-regulated by 99% (P<0.0001). Expression of comE, comD, gtfB and gtfC, genes related to biofilm formation, were down-regulated 8-, 43-, 85- and 298-fold in the murI mutant compared with the wild-type (P<0.0001), respectively. Taken together, the current study provides the first evidence that MurI deficiency adversely affects S. mutans virulence properties, making MurI a potential target for controlling dental caries.

Effect of the association of maltodextrin and sucrose on the acidogenicity and adherence of cariogenic bacteria.

OBJECTIVE: The aim was to investigate the effect of maltodextrin and sucrose association on the acidogenic and adherence profiles of cariogenic bacteria. DESIGN: Streptococcus mutans (S. mutans) and Lactobacillus casei (L. casei) were cultivated in culture medium containing maltodextrin, sucrose, maltodextrin-sucrose mixture or glucose. Analyses of the acidogenicity and microbial adherence were conducted in triplicate for each microorganism and tested carbohydrate. RESULTS: For L. casei, maltodextrin, sucrose and maltodextrin-sucrose mixture showed lower acidogenic potential compared to glucose. When the microorganism was S. mutans, sucrose and maltodextrin-sucrose mixture presented higher acidogenic potential compared to maltodextrin and glucose. Microbial adherence analysis revealed higher adherence for S. mutans in presence of sucrose and maltodextrin-sucrose mixture compared to maltodextrin and glucose. For L. casei, all the carbohydrates showed similar adherence percentages. CONCLUSION: The addition of maltodextrin to sucrose does not increase the cariogenicity of sucrose in terms of acidogenicity and adherence of the cariogenic bacteria.

Potential effect of cationic liposomes on interactions with oral bacterial cells and biofilms.

CONTEXT: Although oral infectious diseases have been attributed to bacteria, drug treatments remain ineffective because bacteria and their products exist as biofilms. Cationic liposomes have been suggested to electrostatically interact with the negative charge on the bacterial surface, thereby improving the effects of conventional drug therapies. However, the electrostatic interaction between oral bacteria and cationic liposomes has not yet been examined in detail. OBJECTIVE: The aim of the present study was to examine the behavior of cationic liposomes and Streptococcus mutans in planktonic cells and biofilms. MATERIALS AND METHODS: Liposomes with or without cationic lipid were prepared using a reverse-phase evaporation method. The zeta potentials of conventional liposomes (without cationic lipid) and cationic liposomes were -13 and 8 mV, respectively, and both had a mean particle size of approximately 180 nm. We first assessed the interaction between liposomes and planktonic bacterial cells with a flow cytometer. We then used a surface plasmon resonance method to examine the binding of liposomes to biofilms. We confirmed the binding behavior of liposomes with biofilms using confocal laser scanning microscopy. RESULTS: The interactions between cationic liposomes and S. mutans cells and biofilms were stronger than those of conventional liposomes. Microscopic observations revealed that many cationic liposomes interacted with the bacterial mass and penetrated the deep layers of biofilms. DISCUSSION AND CONCLUSION: In this study, we demonstrated that cationic liposomes had higher affinity not only to oral bacterial cells, but also biofilms than conventional liposomes. This electrostatic interaction may be useful as a potential drug delivery system to biofilms.

Antibiofilm Activity of Chilean Propolis on Streptococcus mutans Is Influenced by the Year of Collection.

The chemical composition of propolis varies according to factors that could have an influence on its biological properties. Polyphenols from propolis have demonstrated an inhibitory effect on Streptococcus mutans growth. However, it is not known if different years of propolis collection may affect its activity. We aimed to elucidate if the year of collection of propolis influences its activity on Streptococcus mutans. Polyphenol-rich extracts were prepared from propolis collected in three different years, characterized by LC-MS and quantified the content of total polyphenols and flavonoids groups. Finally, was evaluated the antibacterial effect on Streptococcus mutans and the biofilm formation. Qualitative differences were observed in total polyphenols, flavones, and flavonols and the chemical composition between the extracts, affecting the strength of inhibition of biofilm formation but not the antimicrobial assays. In conclusion, chemical composition of propolis depends on the year of collection and influences the strength of the inhibition of biofilm formation.