Antigenic heterogeneity of Bacteroides intermedius as recognized by monoclonal antibodies

Optimal 16S rRNA gene amplicon sequencing analysis for oral microbiota to avoid the potential bias introduced by trimming length, primer, and database

16S rRNA gene amplicon sequencing analysis is used to investigate bacterial communities; however, the estimated bacterial composition can differ from the original due to experimental and analytical biases. Therefore, this study determines the optimal conditions to minimize the potential biases in 16S rRNA gene amplicon sequencing analysis using different DNA samples, trimming lengths, primers, and databases. The results of the mock1 community with 250 and 300 bp paired-end (PE), comprising 15 bacteria from various environments, showed the highest similarity between the theoretical value and the data using the Greengenes2 and the V3 region at the genus level and V5-V6 at the species level. In the 300 bp PE sequencing analysis of the mock2 community, comprising six major oral bacteria, the data using the V3-V4, V4, and V5-V6 regions with the SILVA, Greengenes2, and the Human Oral Microbiome Database (HOMD) showed the highest similarity to the theoretical values at the genus level. At the species level, the data using the V3-V4 and V4 regions with Greengenes2 and the data using the V1-V2 with HOMD exhibited the highest alignment with the theoretical values. In the species analysis of the dental calculus samples with 300 bp PE, the Shannon index value was higher with the V1-V2 region and HOMD than with others. Our results suggest that the optimal conditions for oral microbiome analysis are the combinations of 300 bp PE and the V3-V4 or V4 region with the Greengenes2 and the V1-V2 with HOMD.IMPORTANCEThe 16S rRNA gene amplicon sequencing analysis is frequently used in oral microbiome research. However, this method can have biases that distort the experimental data, which depend on the methodological steps, including sequencing length, trimming length, selected amplification regions, and referenced databases. In this study, a combination of 300 bp PE and the primer targeting the V3-V4 or V4 regions with the Greengenes2 and the V1-V2 region with the HOMD was the most bias-minimizing condition for oral microbiota analysis. In addition, this is the first report of such analyses in modern Japanese dental calculus. The methods used in this study will aid in setting appropriate conditions for sequence analysis of microbiota obtained not only from the oral cavity but also from any environment.

Enhancing Antibiotic Efficacy in Regenerative Endodontics by Improving Biofilm Susceptibility

INTRODUCTION

Various strategies have been researched to enhance the susceptibility of biofilms, given their tolerance to antibiotics. This study evaluated the effect of the anti-microbial peptide nisin in association with antibiotics used in regenerative endodontics, exploring different treatment times and biofilm growth conditions.

METHODS

A mixture of 10 bacterial species was cultivated on dentin specimens anaerobically for 21 days. Biofilms were treated with 1 mL of high-purity nisin Z (nisin ZP, 200 μg/mL) and a triple antibiotic mixture (TAP: ciprofloxacin + metronidazole + minocycline, 5 mg/mL), alone or in combination. The effectiveness of antimicrobial agents was assessed after 1 and 7 days. During the 7-day period, biofilms were treated under 2 conditions: a single dose in a nutrient-depleted setting (ie, no replenishment of growth medium) and multiple doses in a nutrient-rich environment (ie, renewal of medium and antimicrobial agents every 48 h). After treatments, biofilm cells were dispersed, and total colony-forming units were counted.

RESULTS

After 1 d-treatment, nisin ZP + TAP resulted in 2-log cell reduction compared to TAP alone (P < .05). After 7 d-treatment with a single dose, nisin ZP + TAP and TAP reduced bacteria to nonculturable levels (P < .05), whereas repeated antimicrobial doses did not eliminate bacteria in a nutrient-rich environment. No bacterial reduction was observed with nisin ZP alone in any treatment time.

CONCLUSIONS

The additional use of nisin improved the TAP activity only after a short exposure time. Longer exposure to TAP or nisin + TAP in a nutrient-deprived environment effectively eliminated biofilms.

In-vitro polymicrobial oral biofilm model represents clinical microbial profile and disease progression during implant-related infections

AIM

Clinically relevant in-vitro biofilm models are essential and valuable tools for mechanistically dissecting the etiopathogenesis of infectious diseases and test new antimicrobial therapies. Thus, the aim of this study was to develop and test a clinically relevant in-vitro oral polymicrobial biofilm model that mimics implant-related infections in terms of microbial profile.

METHODS AND RESULTS

For this purpose, 24-well plate system was used to model oral biofilms, using three different microbial inoculums to grow in-vitro biofilms: (1) human saliva from periodontally healthy patients; (2) saliva as in inoculum 1 + Porphyromonas gingivalis strain; and (3) supra and subgingival biofilm collected from peri-implant sites of patients diagnosed with peri-implantitis. Biofilms were grown to represent the dynamic transition from an aerobic to anaerobic community profile. Subsequently, biofilms were collected after each phase and evaluated for microbiological composition, microbial counts, biofilm biomass, structure, and susceptibility to chlorhexidine (CHX). Results showed higher live cell count (P < .05) for biofilms developed from patients' biofilm inoculum, but biomass volume, dry weight, and microbiological composition were similar among groups (P > .05). Interestingly, according to the checkerboard DNA-DNA hybridization results, the biofilm developed from stimulated human saliva exhibited a microbial composition more similar to the clinical subgingival biofilm of patients with peri-implantitis, with proportions of the main pathogens closer to those found in the disease. In addition, biofilm developed using saliva as inoculum was shown to be susceptible to CHX with significant reduction in bacteria compared with biofilms without exposure to CHX (P < .05).

CONCLUSION

The findings suggested that the in-vitro polymicrobial biofilm developed from human saliva as inoculum is a suitable model and clinically relevant tool for mimicking the microbial composition of implant-related infections.

Dynamic interactions between Candida albicans and different streptococcal species in a multispecies oral biofilm

The oral cavity is colonized by a plethora of bacteria, fungi, and archaea, including streptococci of the mitis group (MSG) and the yeast Candida albicans. This study aims to investigate the role of streptococcal species in the development of oral biofilm and the cross-kingdom interactions between some of the members of the commensal MSG and the pathogen yeast C. albicans using a multispecies supragingival biofilm model. A total of nine different in vitro biofilms were grown, quantified with culture analyses, and visually examined with confocal laser scanning microscopy (CLSM). A four-species biofilm without any streptococcal species was used as a basic biofilm. In each subsequent inoculum, one species of MSG was added and afterward combined with Streptococcus mutans. The eight-species biofilm contained all eight strains used in this study. Culture analyses showed that the presence of S. mutans in a four-species biofilm with Streptococcus oralis or S. oralis subsp. tigurinus did not differ significantly in C. albicans colony-forming unit (CFU) counts compared to biofilms without S. mutans. However, compared to other mitis species, Streptococcus gordonii combined with S. mutans resulted in the lowest CFUs of C. albicans. Visual observation by CLSM showed that biofilms containing both S. mutans and one species of MSG seemed to induce the formation of filamentous form of C. albicans. However, when several species of MSG were combined with S. mutans, C. albicans was again found in its yeast form.

Antibacterial Electrodeposited Copper-Doped Calcium Phosphate Coatings for Dental Implants

Dental implants provide a good solution for the replacement of tooth roots. However, the full restoration of tooth functions relies on the bone-healing period before positioning the abutment and the crown on the implant, with the associated risk of post-operative infection. This study aimed at developing a homogeneous and adherent thin calcium phosphate antibacterial coating on titanium dental implants by electrodeposition to favor both implant osseointegration and to limit peri-implantitis. By combining global (XRD, FTIR-ATR, elemental titration) and local (SEM, Raman spectroscopy on the coating surface and thickness) characterization techniques, we determined the effect of electrodeposition time on the characteristics and phases content of the coating and the associated mechanism of its formation. The 1-min-electrodeposited CaP coating (thickness: 2 ± 1 μm) was mainly composed of nano-needles of octacalcium phosphate. We demonstrated its mechanical stability after screwing and unscrewing the dental implant in an artificial jawbone. Then, we showed that we can reach a high copper incorporation rate (up to a 27% Cu/(Cu+Ca) molar ratio) in this CaP coating by using an ionic exchange post-treatment with copper nitrate solution at different concentrations. The biological properties (antibiofilm activity and cytotoxicity) were tested in vitro using a model of mixed bacteria biofilm mimicking peri-implantitis and the EN 10993-5 standard (direct contact), respectively. An efficient copper-doping dose was determined, providing an antibiofilm property to the coating without cytotoxic side effects. By combining the electrodeposition and copper ionic exchange processes, we can develop an antibiofilm calcium phosphate coating on dental implants with a tunable thickness and phases content.

Antibiofilm Activity of LL-37 Peptide and D-Amino Acids Associated with Antibiotics Used in Regenerative Endodontics on an Ex Vivo Multispecies Biofilm Model

The antimicrobial peptide LL-37 and D-amino acids (D-AAs) have been proposed as antibiofilm agents. Therefore, this study aimed to test the antimicrobial effect of antibiofilm agents associated with antibiotics used in regenerative endodontic procedures (the triple antibiotic paste—TAP: ciprofloxacin + metronidazole + minocycline). An endodontic-like biofilm model grown on bovine dentin discs was used in this study. After 21-day growth, the biofilms were treated with 1 mg/mL TAP, 10 μM LL-37, an association of LL-37 + TAP, 40 mM D-AAs solution, an association of D-AAs + TAP, and phosphate-buffered saline (negative control). Colony forming unit (CFU) data were analyzed by two-way ANOVA and Tukey’s multiple comparison test (p < 0.05). LL-37 + TAP showed the best antibacterial activity (7-log10 CFU/mL ± 0.5), reaching a 1 log reduction of cells in relation to the negative control (8-log10 CFU/mL ± 0.7) (p < 0.05). In turn, no significant reduction in bacterial cells was observed with TAP, LL-37, D-AAs, and D-AAs + TAP compared to the negative control. In conclusion, the combination of antibiotics and LL-37 peptide showed mild antibacterial activity, while the combination of antibiotics and D-AAs showed no activity against complex biofilms.

Mapping of a Subgingival Dual-Species Biofilm Model Using Confocal Raman Microscopy

Techniques for continuously monitoring the formation of subgingival biofilm, in relation to the determination of species and their accumulation over time in gingivitis and periodontitis, are limited. In recent years, advancements in the field of optical spectroscopic techniques have provided an alternative for analyzing three-dimensional microbiological structures, replacing the traditional destructive or biofilm staining techniques. In this work, we have demonstrated that the use of confocal Raman spectroscopy coupled with multivariate analysis provides an approach to spatially differentiate bacteria in an in vitro model simulating a subgingival dual-species biofilm. The present study establishes a workflow to evaluate and differentiate bacterial species in a dual-species in vitro biofilm model, using confocal Raman microscopy (CRM). Biofilm models of Actinomyces denticolens and Streptococcus oralis were cultured using the “Zürich in vitro model” and were analyzed using CRM. Cluster analysis was used to spatially differentiate and map the biofilm model over a specified area. To confirm the clustering of species in the cultured biofilm, confocal laser scanning microscopy (CLSM) was coupled with fluorescent in vitro hybridization (FISH). Additionally, dense bacteria interface area (DBIA) samples, as an imitation of the clusters in a biofilm, were used to test the developed multivariate differentiation model. This confirmed model was successfully used to differentiate species in a dual-species biofilm and is comparable to morphology. The results show that the developed workflow was able to identify main clusters of bacteria based on spectral “fingerprint region” information from CRM. Using this workflow, we have demonstrated that CRM can spatially analyze two-species in vitro biofilms, therefore providing an alternative technique to map oral multi-species biofilm models.

Low Concentrations of Chlorhexidine Inhibit the Formation and Structural Integrity of Enzyme-Treated Multispecies Oral Biofilms

The self-produced matrix of biofilms, consisting of extracellular polymeric substances, plays an important role in biofilm adhesion to surfaces and the structural integrity of biofilms. In dentistry, biofilms cause multiple diseases such as caries, periodontitis, and pulpitis. Disruption of these biofilms adhering to dental hard tissues may pose a major challenge since biofilms show higher tolerance to antimicrobials and antibiotics than planktonic cells. In this study, the effect of low concentrations of chlorhexidine (CHX) on enzyme-treated multispecies oral biofilm was investigated in an in vitro model. Six-species biofilms were enzymatically treated by anaerobic growth in a medium containing DNase I and proteinase K. Biofilms were exposed to a low concentration of CHX at defined time points. After 64h, biofilms were either harvested and quantified by cultural analyses or stained for confocal laser scanning microscopy (CLSM) analyses using either Live/Dead kit or different fluorescent dyes. A mixture of YoPro1 and SYTOX^™ Green, Fluorescent Brightener 28 (Calcofluor), and SYPRO^™ Ruby Protein Gel Stain was used to stain total DNA, exopolysaccharides, and extracellular proteins, respectively. Extracellular DNA (eDNA) was visualized via an indirect immunofluorescence assay (Mouse anti-DNA IgG, Goat anti-Mouse IgG, Streptavidin-Cy3). Overall, the total colony-forming units significantly decreased after combined treatment with a low concentration of CHX and enzymes compared to the group treated with CHX alone (p<0.001). These findings also apply to five species individually (Streptococcus mutans, Streptococcus oralis, Actinomyces oris, Veillonella dispar, and Candida albicans) occurring in the biofilms, with Fusobacterium nucleatum being the only exception. Furthermore, CLSM images showed less dense biofilms and a reduction in cell numbers after combined treatment compared to the group without enzymes. The combination of enzymes capable of disturbing the matrix integrity with antimicrobial agents thus appears to be a promising approach for biofilm disruption and killing.

Antibacterial Effect of High-Purity Nisin Alone and in Combination with D-Amino Acids or Chlorhexidine in an Endodontic-Like Biofilm Model

New strategies to eradicate endodontic biofilms are needed. Therefore, we evaluated the effect of high-purity nisin alone and in combination with D-amino acids (D-AAs) or chlorhexidine (CHX) against an “endodontic-like” biofilm model. Biofilms were grown on hydroxyapatite discs for 64 h and treated with nisin, eight D-AAs mixture, nisin + eight D-AAs, 2% CHX, and nisin + 2% CHX. After the 5 min and 24 h treatments, biofilm cells were harvested and total colony-forming units were counted. Differences between groups were tested by two-way ANOVA followed by Tukey’s multiple comparisons test (p < 0.05). Nisin and D-AAs, alone or in combination, were not effective in reducing bacteria after short or long exposure times. After 5 min, treatment with 2% CHX and nisin + 2% CHX resulted in 2 and 2.4-log cell reduction, respectively, compared with the no treatment control (p < 0.001). After 24 h, 2% CHX and nisin + 2% CHX drastically reduced bacterial counts. In conclusion, high-purity nisin alone or in combination with D-AAs did not show antibacterial activity against multispecies biofilms. Moreover, combined treatment using nisin and CHX showed similar antibiofilm activity compared with the use of CHX alone.

Extracellular biofilm matrix leads to microbial dysbiosis and reduces biofilm susceptibility to antimicrobials on titanium biomaterial: An in vitro and in situ study

OBJECTIVES

To test the role of exopolysaccharide (EPS) polymers matrix to modulate the composition/virulence of biofilms growing on titanium (Ti) surfaces, the effect on antibiotic susceptibility, and whether a dual-targeting therapy approach for disrupted EPS matrix could improve the antimicrobial effect.

MATERIALS AND METHODS

A microcosm biofilm model using human saliva as inoculum was used, and the microbial composition was assessed by checkerboard DNA-DNA hybridization. EPS-enriched biofilms virulence was tested using fibroblast monolayer. Povidone-iodine (PI) was used as EPS-targeting agent followed by amoxicillin + metronidazole antibiotic to reduce bacterial biomass using an in situ model.

RESULTS

An EPS-enriched environment, obtained by sucrose exposure, promoted bacterial accumulation and led to a dysbiosis on biofilms, favoring the growth of Streptococcus, Fusobacterium, and Campylobacter species and even strict anaerobic species related to peri-implant infections, such as Porphyromonas gingivalis and Tannerella forsythia (~3-fold increase). EPS-enriched biofilm transitioned from a commensal aerobic to a pathogenic anaerobic profile. EPS increased biofilm virulence promoting higher host cell damage and reduced antimicrobial susceptibility, but the use of a dual-targeting approach with PI pre-treatment disrupted EPS matrix scaffold, increasing antibiotic effect on in situ biofilms.

CONCLUSION

Altogether, our data provide new insights of how EPS matrix creates an environment that favors putative pathogens growth and shed light to a promising approach that uses matrix disruption as initial step to potentially improve implant-related infections treatment.

Antimicrobial Effectiveness of Calcium Silicate Sealers against a Nutrient-Stressed Multispecies Biofilm

Purpose: This study compared the antimicrobial efficacy of calcium silicate sealers (BioRoot RCS and Total Fill BC) and conventional sealers (AH Plus and Tubli-seal) against planktonic bacteria and a nutrient-stressed multispecies biofilm. Methods: Antimicrobial properties of freshly mixed sealers were investigated using the direct contact test (DCT) and a nutrient-stressed multispecies biofilm comprised of five endodontic strains. Antimicrobial activity was determined using quantitative viable counts and confocal laser scanning microscopy (CLSM) analysis with live/dead staining. The pH of the sealers was analysed over a period of 28 days in Hanks Balanced Salt Solution (HBSS). Analysis of variance (ANOVA) with Tukey tests and the Kruskal–Wallis test were used for data analysis with a significance of 5%. Results: All endodontic sealers exhibited significant antimicrobial activity against planktonic bacteria (p < 0.05). BioRoot RCS caused a significant reduction in viable counts of the biofilms compared to AH Plus and the control (p < 0.05), while no significant difference could be observed compared to TotalFill BC and Tubli-seal (p > 0.05). CLSM analysis showed that BioRoot RCS and TotalFill BC exhibited significant biofilm inhibition compared to Tubli-seal, AH Plus and the control (p < 0.05). BioRoot RCS presented with the highest microbial killing, followed by TotalFill BC and Tubli-seal. Alkalizing activity was seen from the onset by BioRoot RCS, TotalFill BC and AH Plus. After 28 days, BioRoot RCS demonstrated the highest pH in HBSS (pH > 12). Conclusions: Calcium silicate sealers exhibited effective antimicrobial properties. This was demonstrated by superior biofilm inhibition capacity and microbial killing, with strong alkalizing activity compared to epoxy-based and zinc oxide-eugenol-based sealers.

Confocal Raman microscopy to identify bacteria in oral subgingival biofilm models

The study of oral disease progression, in relation to the accumulation of subgingival biofilm in gingivitis and periodontitis is limited, due to either the ability to monitor plaque in vitro. When compared, optical spectroscopic techniques offer advantages over traditional destructive or biofilm staining approaches, making it a suitable alternative for the analysis and continued development of three-dimensional structures. In this work, we have developed a confocal Raman spectroscopy analysis approach towards in vitro subgingival plaque models. The main objective of this study was to develop a method for differentiating multiple oral subgingival bacterial species in planktonic and biofilm conditions, using confocal Raman microscopy. Five common subgingival bacteria (Fusobacterium nucleatum, Streptococcus mutans, Veillonella dispar, Actinomyces naeslundii and Prevotella nigrescens) were used and differentiated using a 2-way orthogonal Partial Least Square with Discriminant Analysis (O2PLS-DA) for the collected spectral data. In addition to planktonic growth, mono-species biofilms cultured using the 'Zürich Model' were also analyzed. The developed method was successfully used to predict planktonic and mono-species biofilm species in a cross validation setup. The results show differences in the presence and absence of chemical bands within the Raman spectra. The O2PLS-DA model was able to successfully predict 100% of all tested planktonic samples and 90% of all mono-species biofilm samples. Using this approach we have shown that Confocal Raman microscopy can analyse and predict the identity of planktonic and mono-species biofilm species, thus enabling its potential as a technique to map oral multi-species biofilm models.

Endodontic-Like Oral Biofilms as Models for Multispecies Interactions in Endodontic Diseases

Oral bacteria possess the ability to form biofilms on solid surfaces. After the penetration of oral bacteria into the pulp, the contact between biofilms and pulp tissue may result in pulpitis, pulp necrosis and/or periapical lesion. Depending on the environmental conditions and the availability of nutrients in the pulp chamber and root canals, mainly Gram-negative anaerobic microorganisms predominate and form the intracanal endodontic biofilm. The objective of the present study was to investigate the role of different substrates on biofilm formation as well as the separate and collective incorporation of six endodontic pathogens, namely Enterococcus faecalis, Staphylococcus aureus, Prevotella nigrescens, Selenomonas sputigena, Parvimonas micra and Treponema denticola into a nine-species "basic biofilm". This biofilm was formed in vitro as a standard subgingival biofilm, comprising Actinomyces oris, Veillonella dispar, Fusobacterium nucleatum, Streptococcus anginosus, Streptococcus oralis, Prevotella intermedia, Campylobacter rectus, Porphyromonas gingivalis, and Tannerella forsythia. The resulting endodontic-like biofilms were grown 64 h under the same conditions on hydroxyapatite and dentin discs. After harvesting the endodontic-like biofilms, the bacterial growth was determined using quantitative real-time PCR, were labeled using fluorescence in situ hybridization (FISH) and analyzed by confocal laser scanning microscopy (CLSM). The addition of six endodontic pathogens to the "basic biofilm" induced a decrease in the cell number of the "basic" species. Interestingly, C. rectus counts increased in biofilms containing E. faecalis, S. aureus, P. nigrescens and S. sputigena, respectively, both on hydroxyapatite and on dentin discs, whereas P. intermedia counts increased only on dentin discs by addition of E. faecalis. The growth of E. faecalis on hydroxyapatite discs and of E. faecalis and S. aureus on dentin discs were significantly higher in the biofilm containing all species than in the "basic biofilm". Contrarily, the counts of P. nigrescens, S. sputigena and P. micra on hydroxyapatite discs as well as counts of P. micra and T. denticola on dentin discs decreased in the all-species biofilm. Overall, all bacterial species associated with endodontic infections were successfully incorporated into the standard multispecies biofilm model both on hydroxyapatite and dentin discs. Thus, future investigations on endodontic infections can rely on this newly established endodontic-like multispecies biofilm model.

The synthesis of nano silver-graphene oxide system and its efficacy against endodontic biofilms using a novel tooth model

OBJECTIVE

The deleterious caustic effects of sodium hypochlorite (NaOCl) as a root canal irrigant makes it imperative that alternative methods are developed for root canal disinfection. The purpose of this study was to examine the antimicrobial efficacy of silver nanoparticles (AgNPs) synthesized on an aqueous graphene oxide (GO) matrix (Ag-GO), with different irrigant delivery methods to enhance the disinfection regimen, using a novel ex vivo infected tooth model.

METHODS

AgNPs were prepared by reducing AgNO₃ with 0.01M NaBH₄ in presence of GO. Elemental analysis was performed with scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and scanning transmission electron microscopy (STEM) was used for size and morphology analysis of GO and Ag-GO. Nutrient stressed, multi-species biofilms were grown in prepared root canals of single-rooted teeth. The irrigants used were sterile saline, 1% and 2.5% NaOCl, 2% chlorhexidine gluconate (CHX), 17% EDTA and an aqueous suspension of 0.25% Ag-GO. The antimicrobial efficacy of the irrigants were performed with paper point sampling and measurement of microbial counts. The biofilm disruption in dentine tubule surfaces was analysed with confocal laser scanning microscopy (CLSM). The acquisition of total biovolume (μm³/μm²) and biofilm viability was performed using software BioImage_L. Two-way analysis of variance (ANOVA) with post hoc Tukey tests was used for data analysis with level of statistical significance set at P<0.05.

RESULTS

SEM/EDS analysis confirmed impregnation of Ag within the GO matrix. TEM images showed polygonal GO sheets and spherical AgNPs of diameter 20-50nm, forming a network on the surface of GO sheets. The use of ultrasonic activation enhanced the efficacy of Ag-GO compared to 1% NaOCl, 2% CHX, 17% EDTA and sterile saline (P<0.05). The microbial killing efficacy of 2.5% NaOCl was superior compared to the experimental groups. The maximum biofilm disruption, in dentine tubule surfaces, was achieved by 2.5% NaOCl, however Ag-GO caused a significant reduction of total biovolumes compared to the rest of the experimental groups (P<0.05%).

SIGNIFICANCE

The successful documentation of the microbial killing and biofilm disruption capacity of Ag-GO is a promising step forward to explore its unique properties in clinical applications and biomaterials in dentistry.

Visible-Light-Induced Photocatalytic and Antibacterial Activity of TiO2 Codoped with Nitrogen and Bismuth: New Perspectives to Control Implant-Biofilm-Related Diseases

Biofilm-associated diseases are one of the main causes of implant failure. Currently, the development of implant surface treatment goes beyond the osseointegration process and focuses on the creation of surfaces with antimicrobial action and with the possibility to be re-activated (i.e., light source activation). Titanium dioxide (TiO₂), an excellent photocatalyst used for photocatalytic antibacterial applications, could be a great alternative, but its efficiency is limited to the ultraviolet (UV) range of the electromagnetic spectrum. Since UV radiation has carcinogenic potential, we created a functional TiO₂ coating codoped with nitrogen and bismuth via the plasma electrolytic oxidation (PEO) of titanium to achieve an antibacterial effect under visible light with re-activation potential. A complex surface topography was demonstrated by scanning electron microscopy and three-dimensional confocal laser scanning microscopy. Additionally, PEO-treated surfaces showed greater hydrophilicity and albumin adsorption compared to control, untreated titanium. Bismuth incorporation shifted the band gap of TiO₂ to the visible region and facilitated higher degradation of methyl orange (MO) in the dark, with a greater reduction in the concentration of MO after visible-light irradiation even after 72 h of aging. These results were consistent with the in vitro antibacterial effect, where samples with nitrogen and bismuth in their composition showed the greatest bacterial reduction after 24 h of dual-species biofilm formation ( Streptococcus sanguinis and Actinomyces naeslundii) in darkness with a superior effect at 30 min of visible-light irradiation. In addition, such a coating presents reusable photocatalytic potential and good biocompatibility by presenting a noncytotoxicity effect on human gingival fibroblast cells. Therefore, nitrogen and bismuth incorporation into TiO₂ via PEO can be considered a promising alternative for dental implant application with antibacterial properties in darkness, with a stronger effect after visible-light application.

Antimicrobial efficacy of alternative compounds for use in oral care toward biofilms from caries-associated bacteria in vitro

For caries‐active patients, antimicrobial measures may be useful in addition to mechanical biofilm removal. The aim of this study was to investigate the antimicrobial efficacy of alternative compounds for use in oral care from two main categories (i.e., preservatives and natural compounds) toward biofilms from caries‐associated bacteria as compared to oral care gold‐standards chlorhexidine digluconate (CHX), cetylpyridinium chloride (CPC), and zinc. Compounds were screened in initial Streptococcus mutans biofilms. Then, the most effective compounds were further investigated in mature S. mutans and polymicrobial biofilms comprising Actinomyces naeslundii, Actinomyces odontolyticus, and S. mutans. Here, distinct treatment periods and concentrations were evaluated. Biofilms were visualized by scanning electron microscopy and bacterial membrane damage was evaluated by means of flow cytometry and staining with SYBR Green and propidium iodide. Citrus extract was the only compound exhibiting similar antimicrobial efficacy in initial S. mutans biofilms (>5 log₁₀) as compared to CHX and CPC, but its effect was clearly inferior in mature S. mutans and polymicrobial biofilms. Flow cytometric data suggested that the mechanism of antimicrobial action of citrus extract may be based on damage of bacterial membranes similar to CHX and CPC. From all alternative compounds investigated in this study, citrus extract exhibited the highest antimicrobial efficacy toward in vitro biofilms from caries‐associated bacteria, but still was less effective than oral care gold‐standard antiseptics CHX and CPC. Nevertheless, citrus extract may be a valuable antimicrobial compound for use in oral care for caries‐active patients.

Phenalen-1-one-Mediated Antimicrobial Photodynamic Therapy: Antimicrobial Efficacy in a Periodontal Biofilm Model and Flow Cytometric Evaluation of Cytoplasmic Membrane Damage

In light of increasing resistance toward conventional antibiotics and antiseptics, antimicrobial photodynamic therapy (aPDT) may be a valuable alternative, especially for use in dentistry. In this regard, photosensitizers (PS) based on a phenalen-1-one structure seem to be especially favorable due to their high singlet oxygen quantum yield. However, the actual target structures of phenalen-1-one-mediated aPDT are still unclear. The aim of the present study was to investigate the antimicrobial efficacy of aPDT mediated by phenalen-1-one derivatives SAPYR and SAGUA for inactivation of a polymicrobial biofilm consisting of three putative periodontal pathogens in vitro and to get first insights in the mechanism of action of phenalen-1-one-mediated aPDT by assessing damage of cytoplasmic membranes. aPDT with SAPYR exhibited identical antimicrobial efficacy as compared to chlorhexidine (CHX) [4.4-6.1 log₁₀ reduction of colony forming units (CFUs) depending on bacterial species] while aPDT with SAGUA was less effective (2.0-2.8 log₁₀). Flow cytometric analysis combined with propidium iodide (PI) staining revealed no damage of cytoplasmic membranes after aPDT with both phenalen-1-one derivatives, which was confirmed by spectroscopic measurements for release of nucleic acids after treatment. Spectrophotometric PS-uptake measurements showed no uptake of SAPYR by bacterial cells. Despite the inability to pinpoint the actual target of phenalen-1-one-mediated aPDT, this study shows the high antimicrobial potential of phenalen-1-on mediated aPDT (especially when using SAPYR) and represents a first step for getting insights in the mechanism and damage patterns of aPDT with this class of PS.

Behavior of two Tannerella forsythia strains and their cell surface mutants in multispecies oral biofilms

As a member of subgingival multispecies biofilms, Tannerella forsythia is commonly associated with periodontitis. The bacterium has a characteristic cell surface (S-) layer modified with a unique O-glycan. Both the S-layer and the O-glycan were analyzed in this study for their role in biofilm formation by employing an in vitro multispecies biofilm model mimicking the situation in the oral cavity. Different T. forsythia strains and mutants with characterized defects in cell surface composition were incorporated into the model, together with nine species of select oral bacteria. The influence of the T. forsythia S-layer and attached glycan on the bacterial composition of the biofilms was analyzed quantitatively using colony-forming unit counts and quantitative real-time polymerase chain reaction, as well as qualitatively by fluorescence in situ hybridization and confocal laser scanning microscopy. This revealed that changes in the T. forsythia cell surface did not affect the quantitative composition of the multispecies consortium, with the exception of Campylobacter rectus cell numbers. The localization of T. forsythia within the bacterial agglomeration varied depending on changes in the S-layer glycan, and this also affected its aggregation with Porphyromonas gingivalis. This suggests a selective role for the glycosylated T. forsythia S-layer in the positioning of this species within the biofilm, its co-localization with P. gingivalis, and the prevalence of C. rectus. These findings might translate into a potential role of T. forsythia cell surface structures in the virulence of this species when interacting with host tissues and the immune system, from within or beyond the biofilm.

Bifidobacteria inhibit the growth of Porphyromonas gingivalis but not of Streptococcus mutans in an in vitro biofilm model

There is growing interest in the use of probiotic bifidobacteria for enhancement of the therapy, and in the prevention, of oral microbial diseases. However, the results of clinical studies assessing the effects of bifidobacteria on the oral microbiota are controversial, and the mechanisms of actions of probiotics in the oral cavity remain largely unknown. In addition, very little is known about the role of commensal bifidobacteria in oral health. Our aim was to study the integration of the probiotic Bifidobacterium animalis subsp. lactis Bb12 and of oral Bifidobacterium dentium and Bifidobacterium longum isolates in supragingival and subgingival biofilm models and their effects on other bacteria in biofilms in vitro using two different in vitro biofilms and agar-overlay assays. All bifidobacteria integrated well into the subgingival biofilms composed of Porphyromonas gingivalis, Actinomyces naeslundii, and Fusobacterium nucleatum and decreased significantly only the number of P. gingivalis in the biofilms. The integration of bifidobacteria into the supragingival biofilms containing Streptococcus mutans and A. naeslundii was less efficient, and bifidobacteria did not affect the number of S. mutans in biofilms. Therefore, our results suggest that bifidobacteria may have a positive effect on subgingival biofilm and thereby potential in enhancing gingival health; however, their effect on supragingival biofilm may be limited.

Incorporation of staphylococci into titanium-grown biofilms: an in vitro "submucosal" biofilm model for peri-implantitis

Objectives

Staphylococcus spp. are postulated to play a role in peri‐implantitis. This study aimed to develop a “submucosal” in vitro biofilm model, by integrating two staphylococci into its composition.

Materials and methods

The standard “subgingival” biofilm contained Actinomyces oris, Fusobacterium nucleatum, Streptococcus oralis, Veillonella dispar, Campylobacter rectus, Prevotella intermedia, Streptococcus anginosus, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola, and was further supplemented with Staphyoccous aureus and/or Staphylococcus epidermidis. Biofilms were grown anaerobically on hydroxyapatite or titanium discs and harvested after 64 h for real‐time polymerase chain reaction, to determine their composition. Confocal laser scanning microscopy and fluorescence in situ hybridization were used for identifying the two staphylococci within the biofilm.

Results

Both staphylococci established within the biofilms when added separately. However, when added together, only S. aureus grew in high numbers, whereas S. epidermidis was reduced almost to the detection limit. Compared to the standard subgingival biofilm, addition of the two staphylococci had no impact on the qualitative or quantitative composition of the biofilm. When grown individually in the biofilm, S. epidermidis and S. aureus formed small distinctive clusters and it was confirmed that S. epidermidis was not able to grow in presence of S. aureus.

Conclusions

Staphyoccous aureus and S. epidermidis can be individually integrated into an oral biofilm grown on titanium, hence establishing a “submucosal” biofilm model for peri‐implantitis. This model also revealed that S. aureus outcompetes S. epidermidis when grown together in the biofilm, which may explain the more frequent association of the former with peri‐implantitis.

Microbial dynamics during conversion from supragingival to subgingival biofilms in an in vitro model

The development of dental caries and periodontal diseases result from distinct shifts in the microbiota of the tooth-associated biofilm. This in vitro study aimed to investigate changes in biofilm composition and structure, during the shift from a 'supragingival' aerobic profile to a 'subgingival' anaerobic profile. Biofilms consisting of Actinomyces oris, Candida albicans, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus mutans and Veillonella dispar were aerobically grown in saliva-containing medium on hydroxyapatite disks. After 64 h, Campylobacter rectus, Prevotella intermedia and Streptococcus anginosus were further added along with human serum, while culture conditions were shifted to microaerophilic. After 96 h, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola were finally added and the biofilm was grown anaerobically for another 64 h. At the end of each phase, biofilms were harvested for species-specific quantification and localization. Apart from C. albicans, all other species gradually increased during aerobic and microaerophilic conditions, but remained steady during anaerobic conditions. Biofilm thickness was doubled during the microaerophilic phase, but remained steady throughout the anaerobic phase. Extracellular polysaccharide presence was gradually reduced throughout the growth period. Biofilm viability was reduced during the microaerophilic conversion, but was recovered during the anaerobic phase. This in vitro study has characterized the dynamic structural shifts occurring in an oral biofilm model during the switch from aerobic to anaerobic conditions, potentially modeling the conversion of supragingival to subgingival biofilms. Within the limitations of this experimental model, the findings may provide novel insights into the ecology of oral biofilms.

Quantitative proteomics reveal distinct protein regulations caused by Aggregatibacter actinomycetemcomitans within subgingival biofilms

Periodontitis is an infectious disease that causes the inflammatory destruction of the tooth-supporting (periodontal) tissues, caused by polymicrobial biofilm communities growing on the tooth surface. Aggressive periodontitis is strongly associated with the presence of Aggregatibacter actinomycetemcomitans in the subgingival biofilms. Nevertheless, whether and how A. actinomycetemcomitans orchestrates molecular changes within the biofilm is unclear. The aim of this work was to decipher the interactions between A. actinomycetemcomitans and other bacterial species in a multi-species biofilm using proteomic analysis. An in vitro 10-species "subgingival" biofilm model, or its derivative that included additionally A. actinomycetemcomitans, were anaerobically cultivated on hydroxyapatite discs for 64 h. When present, A. actinomycetemcomitans formed dense intra-species clumps within the biofilm mass, and did not affect the numbers of the other species in the biofilm. Liquid chromatography-tandem mass spectrometry was used to identify the proteomic content of the biofilm lysate. A total of 3225 and 3352 proteins were identified in the biofilm, in presence or absence of A. actinomycetemcomitans, respectively. Label-free quantitative proteomics revealed that 483 out of the 728 quantified bacterial proteins (excluding those of A. actinomycetemcomitans) were accordingly regulated. Interestingly, all quantified proteins from Prevotella intermedia were up-regulated, and most quantified proteins from Campylobacter rectus, Streptococcus anginosus, and Porphyromonas gingivalis were down-regulated in presence of A. actinomycetemcomitans. Enrichment of Gene Ontology pathway analysis showed that the regulated groups of proteins were responsible primarily for changes in the metabolic rate, the ferric iron-binding, and the 5S RNA binding capacities, on the universal biofilm level. While the presence of A. actinomycetemcomitans did not affect the numeric composition or absolute protein numbers of the other biofilm species, it caused qualitative changes in their overall protein expression profile. These molecular shifts within the biofilm warrant further investigation on their potential impact on its virulence properties, and association with periodontal pathogenesis.

Establishment of an oral infection model resembling the periodontal pocket in a perfusion bioreactor system

Periodontal infection involves a complex interplay between oral biofilms, gingival tissues and cells of the immune system in a dynamic microenvironment. A humanized in vitro model that reduces the need for experimental animal models, while recapitulating key biological events in a periodontal pocket, would constitute a technical advancement in the study of periodontal disease. The aim of this study was to use a dynamic perfusion bioreactor in order to develop a gingival epithelial-fibroblast-monocyte organotypic co-culture on collagen sponges. An 11 species subgingival biofilm was used to challenge the generated tissue in the bioreactor for a period of 24 h. The histological and scanning electron microscopy analysis displayed an epithelial-like layer on the surface of the collagen sponge, supported by the underlying ingrowth of gingival fibroblasts, while monocytic cells were also found within the sponge mass. Bacterial quantification of the biofilm showed that in the presence of the organotypic tissue, the growth of selected biofilm species, especially Campylobacter rectus, Actinomyces oris, Streptococcus anginosus, Veillonella dispar, and Porphyromonas gingivalis, was suppressed, indicating a potential antimicrobial effect by the tissue. Multiplex immunoassay analysis of cytokine secretion showed that interleukin (IL)-1 β, IL-2, IL-4, and tumor necrosis factor (TNF)-α levels in cell culture supernatants were significantly up-regulated in presence of the biofilm, indicating a positive inflammatory response of the organotypic tissue to the biofilm challenge. In conclusion, this novel host-biofilm interaction organotypic model might resemble the periodontal pocket and have an important impact on the study of periodontal infections, by minimizing the need for the use of experimental animal models.

Intracanal Antibiotic Medication for Sustained Root Surface Disinfection-A Laboratory Evaluation

Purpose:

To measure the release of an antibiotic mixture of ciprofloxacin, cerfuroxim and metronidazole (TreVitaMix, TVM) through human dentine and to assess the growth inhibition of Fusobacterium nucleatum.

Material and Methods:

Twenty-four extracted human incisors were scaled and endodontically treated. Root canals were either filled with antibiotic tri-mixture (TVM) or with the carrier material alone (propylene glycol, PG) and were coronally and apically sealed with a flowable composite. Transradicular medicament release was spectrophotometrically measured at 277 nm in simulated body fluid for up to 21 days. In a second part, an agar diffusion assay (F. nucleatum) with representative TVM concentrations as determined in the first part was performed to study the growth inhibition. Samples were anaerobical incubated for 48 h and inhibition zones were measured.

Results:

TVM was spectrophotometrically detectable in the immersion solution and released in decreasing concentrations up to 21 days (222.5 ± 65.2 mg/ml at day 1 and 35.1 ± 15.6 mg/ml at day 21). In addition, inhibition zones were shown in the agar diffusion assay at representative TVM concentrations. The carrier material showed no antibacterial effect.

Conlusion:

TVM showed the potential to penetrate through dentine and to inhibit bacterial growth. Therefore, it might have the potential to disinfect the outer root surface in perio-endo lesions, but further research is needed to confirm these observations.

In vitro evaluation of a novel biofilm remover

OBJECTIVE

To evaluate a novel device for its efficacy in removing experimental biofilm from root surfaces and its potential for concomitantly removing/roughening the surface substance.

METHODS AND MATERIALS

A novel acrylic rotary device (biofilm remover, BR) was tested in vitro in three experiments: surface loss, surface roughness [positive controls: Perioset (PS) and Proxoshape (PR)] and biofilm removal [positive controls: ultrasonic (US) and PS]. Surface loss/surface roughness was evaluated for dentin samples instrumented for three 20 s periods. The calcium removed during instrumentation was analysed after each interval and cumulatively, using atomic absorption spectrophotometry (AAS). Surface roughness was measured using profilometric analysis. Biofilm removal was evaluated on dentin specimens coated with a 64.5 h 6-species in vitro formed biofilm, after one 20 s treatment. Surface loss was analysed using anova with Scheffé post hoc test, and surface roughness/biofilm removal was analysed using Mann-Whitney test (all P ≤ 0.05).

RESULTS

Significantly less substance loss [μg (± 1 SD)] was observed with the novel device at all time points, both interval and cumulative (1.0 (± 0.5) versus 9.3 (± 3.2) PS and 9.9 (± 1.9) PR at 60 s). Surface roughness [μm (95% CI)] was significantly lower for BR than for PS and PR [0.00 (-0.01, 0.08) 0.20 (0.16, 0.27) and 0.21 (0.19, 0.24) at 60 s]. Significantly less biofilm bacteria remained after treatment with both BR 4.5 (-0.1, 16.2) and US 1.9 (-0.2, 14.3), compared to PS 52 (27.9, 82.1).

CONCLUSIONS

The novel biofilm remover was less damaging to dentin surfaces, while removing biofilm at least as effectively as devices used in this study.

Role of Porphyromonas gingivalis gingipains in multi-species biofilm formation

Background

Periodontal diseases are polymicrobial diseases that cause the inflammatory destruction of the tooth-supporting (periodontal) tissues. Their initiation is attributed to the formation of subgingival biofilms that stimulate a cascade of chronic inflammatory reactions by the affected tissue. The Gram-negative anaerobes Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola are commonly found as part of the microbiota of subgingival biofilms, and they are associated with the occurrence and severity of the disease. P. gingivalis expresses several virulence factors that may support its survival, regulate its communication with other species in the biofilm, or modulate the inflammatory response of the colonized host tissue. The most prominent of these virulence factors are the gingipains, which are a set of cysteine proteinases (either Arg-specific or Lys-specific). The role of gingipains in the biofilm-forming capacity of P. gingivalis is barely investigated. Hence, this in vitro study employed a biofilm model consisting of 10 “subgingival” bacterial species, incorporating either a wild-type P. gingivalis strain or its derivative Lys-gingipain and Arg-gingipan isogenic mutants, in order to evaluate quantitative and qualitative changes in biofilm composition.

Results

Following 64 h of biofilm growth, the levels of all 10 species were quantified by fluorescence in situ hybridization or immunofluorescence. The wild-type and the two gingipain-deficient P. gingivalis strains exhibited similar growth in their corresponding biofilms. Among the remaining nine species, only the numbers of T. forsythia were significantly reduced, and only when the Lys-gingipain mutant was present in the biofilm. When evaluating the structure of the biofilm by confocal laser scanning microscopy, the most prominent observation was a shift in the spatial arrangement of T. denticola, in the presence of P. gingivalis Arg-gingipain mutant.

Conclusions

The gingipains of P. gingivalis may qualitatively and quantitatively affect composition of polymicrobial biofilms. The present experimental model reveals interdependency between the gingipains of P. gingivalis and T. forsythia or T. denticola.

Integration of non-oral bacteria into in vitro oral biofilms

Biofilms are polymicrobial communities that grow on surfaces in nature. Oral bacteria can spontaneously form biofilms on the surface of teeth, which may compromise the health of the teeth, or their surrounding (periodontal) tissues. While the oral bacteria exhibit high tropism for their specialized ecological niche, it is not clear if bacteria that are not part of the normal oral microbiota can efficiently colonize and grow within oral biofilms. By using an in vitro "supragingival" biofilm model of 6 oral species, this study aimed to investigate if 3 individual bacterial species that are not part of the normal oral microbiota (Eschericia coli, Staphylococcus aureus, Enterococcus faecails) and one not previously tested oral species (Aggregatibacter actinomycetemcomitans) can be incorporated into this established supragingival biofilm model. Staphylococcus aureus and A. actinomycetemcomitans were able to grow efficiently in the biofilm, without disrupting the growth of the remaining species. They localized in sparse small aggregates within the biofilm mass. Enterococcus faecalis and E. coli were both able to populate the biofilm at high numbers, and suppressed the growth of A. oris and S. mutants. Enterococcus faecalis was arranged in a chain-like conformation, whereas E. coli was densely and evenly spread throughout the biofilm mass. In conclusion, it is possible for selected species that are not part of the normal oral microbiota to be introduced into an oral biofilm, under the given experimental micro-environmental conditions. Moreover, the equilibrated incorporation of A. actinomycetemcomitans and S. aureus in this oral biofilm model could be a useful tool in the study of aggressive periodontitis and peri-implantitis, in which these organisms are involved, respectively.

Flow cytometric assessment of Streptococcus mutans viability after exposure to blue light-activated curcumin

BACKGROUND

Streptococcus mutans biofilms are considered as primary causative agents of dental caries. Photodynamic antimicrobial chemotherapy (PACT) has been recently proposed as a strategy for inactivating dental biofilms. This study aimed to investigate the effect of blue light-activated curcumin on S. mutans viability and to explore its potential as a new anti-caries therapeutic agent. The effect of different concentrations and incubation times of photo-activated curcumin on the survival of S. mutans in planktonic and biofilm models of growth was assessed by flow cytometry.

METHODS

Streptococcus mutans in planktonic suspensions or biofilms formed on hydroxyapatite disks were incubated for 5 or 10min with curcumin prior to blue light activation. Bacteria were labeled with SYTO 9 and propidium iodide before viability was assessed by flow cytometry. Results were statistically analyzed using one-way ANOVA and Tukey multiple comparison intervals (α=0.05).

RESULTS

For planktonic cultures, 0.2μM of light-activated curcumin significantly reduced S. mutans viability (p<0.05). For biofilm cultures, light-activated curcumin at concentration of 40-60μM only suppressed viability by 50% (p<0.05). Independently of the mode of growth, incubation time has no significant effect on PACT efficiency.

CONCLUSION

This study indicates that blue light-activated curcumin can efficiently inactivate planktonic cultures of S. mutans whereas biofilms were more resistant to treatment. Flow cytometry allowed the detection of bacteria with damaged membranes that were unable to replicate and grow after cell sorting. Further studies seem warranted to optimize the efficacy of light-activated curcumin against S. mutans biofilms.

Mechanical and hydrodynamic homecare devices to clean rough implant surfaces - an in vitro polyspecies biofilm study

OBJECTIVES

To investigate the cleaning efficacy of a mechanical and a hydrodynamic homecare device on biofilm-coated titanium surfaces with and without chlorhexidine.

MATERIAL AND METHODS

Six-species biofilms were grown on 108 SLA-titanium discs, which were cleaned as follows: sonic toothbrush alone (i) or in combination with either a 0.2% chlorhexidine (ii) or a placebo gel (iii) and oral irrigator (hydrodynamic action) with water (iv) or combined with 0.2% chlorhexidine solution (v). Untreated samples served as control (vi). Biofilms were then harvested either immediately after treatment (study part A) or after a regrowth phase of 24 h (study part B) and colony-forming units (CFU) were assessed. Results were analysed using Whitney U-tests between the treatment groups. After the Bonferroni correction, the significance level was set at α = 0.0033.

RESULTS

The median CFU counts directly after instrumentation accounted - in ascending order (P-values in comparison with the control group A6 were <0.001 for all groups except for A3: P = 0.014) - 2.0E1 (A5), 1.1E5 (A4), 3.6E5 (A2), 3.3E5 (A1) and 6.8E6 (A3), respectively. The untreated control group showed the highest CFU counts: 1.8E7 (A6). After regrowth, the following CFU counts were measured in ascending order (all P-values <0.001 when compared to the control group B6 = 2.0E8): 1.6E2 (B5), 1.9E5 (B2), 1.4E7 (B4), 3.1E7 (B1) and 3.9E7 (B3).

CONCLUSIONS

An oral irrigator combined with 0.2% chlorhexidine is effective in reducing biofilms attached to rough titanium surfaces immediately after cleaning. Following a regrowth phase of 24 h, micro-organisms could be equally effective removed with a sonic toothbrush combined with 0.2% chlorhexidine and an oral irrigator with 0.2% chlorhexidine.

Colonisation of gingival epithelia by subgingival biofilms in vitro: role of "red complex" bacteria

OBJECTIVES

Biofilm formation on tooth surface results in colonisation and invasion of the juxtaposed gingival tissue, eliciting strong inflammatory responses that lead to periodontal disease. This in vitro study investigated the colonisation of human gingival multi-layered epithelium by multi-species subgingival biofilms, and evaluated the relative effects of the "red complex" species (Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola).

METHODS

The grown biofilm consisted of Fusobacterium nucleatum, Campylobacter rectus, Veillonella dispar, P. gingivalis, Prevotella intermedia, T. forsythia, T. denticola, Actinomyces oris, Streptococcus anginosus and Streptococcus oralis, or its variant lacking the "red complex". After 48h in co-culture with the gingival epithelia, the bacterial species in the biofilm were quantified, whereas their localisation on the cell surface was investigated by combining confocal-laser scanning microscopy (CLSM) and fluorescence in situ hybridisation (FISH), as well as by scanning electron microscopy (SEM).

RESULTS

Exclusion of the "red complex" quantitatively affected S. oralis, but not other species. The "red-complex" species were all able to colonise the gingival epithelial cells. A co-localisation trend was observed between P. gingivalis and T. denticola, as determined by FISH. However, in the absence of all three "red complex" bacteria from the biofilm, an immense colonisation of streptococci (potentially S. oralis) was observed on the gingival epithelia, as confirmed by both CLSM and SEM.

CONCLUSIONS

While the "red complex" species synergise in colonizing gingival epithelia, their absence from the biofilm enhances streptococcal colonisation. This antagonism with streptococci reveals that the "red complex" may regulate biofilm virulence, with potential implications in periodontal pathogenesis.

Red wine and oenological extracts display antimicrobial effects in an oral bacteria biofilm model

The antimicrobial effects of red wine and its inherent components on oral microbiota were studied by using a 5-species biofilm model of the supragingival plaque that includes Actinomyces oris, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus mutans and Veillonella dispar. Microbiological analysis (CFU counting and confocal laser scanning microscopy) of the biofilms after the application of red wine, dealcoholized red wine, and red wine extract solutions spiked or not with grape seed and inactive dry yeast extracts showed that the solutions spiked with seed extract were effective against F. nucleatum, S. oralis and A. oris. Also, red wine and dealcoholized wine had an antimicrobial effect against F. nucleatum and S. oralis. Additional experiments showed almost complete and early degradation of flavan-3-ol precursors [(+)-catechin and procyanidin B2] when incubating biofilms with the red wine extract. To our knowledge, this is the first study of antimicrobial properties of wine in an oral biofilm model.

Validation of a quantitative real-time PCR assay and comparison with fluorescence microscopy and selective agar plate counting for species-specific quantification of an in vitro subgingival biofilm model

BACKGROUND AND OBJECTIVE

Subgingival biofilms are the prime etiological factor of periodontal disease. Owing to their complex polymicrobial nature, quantification of individual bacterial species within the biofilm for research and diagnostic purposes can be methodologically challenging. The aims of this study were to establish a quantitative real-time PCR (qPCR) assay to quantify the bacteria used in our 10-species in vitro 'subgingival' biofilm model and to compare the quantitative outcome with fluorescence microscopy and colony-forming unit (CFU) counts on selective agar plates.

MATERIAL AND METHODS

The 10 species included in the in vitro biofilm were Streptococcus oralis, Streptococcus anginosus, Veillonella dispar, Fusobacterium nucleatum, Treponema denticola, Tannerella forsythia, Actinomyces oris, Campylobacter rectus, Porphyromonas gingivalis and Prevotella intermedia. The numbers of each species were quantified at two time points using qPCR, microscopy counting following fluorescence in-situ hybridization (FISH) or immunofluorescence staining, and counting of CFUs after growth on selective agar plates.

RESULTS

All 10 species were successfully quantified using qPCR and FISH or immunofluorescence, and the eight species culturable on selective agar plates were also quantified by counting the numbers of CFUs after growth on selective agar. In early biofilm cultures, all methods showed a significant correlation, although the absolute numbers differed between methods. In late biofilm cultures, measurements obtained using qPCR and FISH or immunofluorescence, but not by CFU counts, maintained significant correlation. CFU counts yielded lower values than did measurements made using the other two methods.

CONCLUSION

Quantitative PCR and epifluorescence microscopy can be easily combined with each other to determine species-specific bacterial numbers within biofilms. However, conventional bacterial cultures cannot be as efficiently combined using these molecular detection methods. This may be crucial in designing and selecting appropriate clinical diagnostic methods for subgingival biofilm samples.

Advancement of the 10-species subgingival Zurich biofilm model by examining different nutritional conditions and defining the structure of the in vitro biofilms

Background

Periodontitis is caused by a highly complex consortium of bacteria that establishes as biofilms in subgingival pockets. It is a disease that occurs worldwide and its consequences are a major health concern. Investigations in situ are not possible and the bacterial community varies greatly between patients and even within different loci. Due to the high complexity of the consortium and the availability of samples, a clear definition of the pathogenic bacteria and their mechanisms of pathogenicity are still not available. In the current study we addressed the need of a defined model system by advancing our previously described subgingival biofilm model towards a bacterial composition that reflects the one observed in diseased sites of patients and analysed the structure of these biofilms.

Results

We further developed the growth media by systematic variation of key components resulting in improved stability and the firm establishment of spirochetes in the 10-species subgingival Zurich biofilm model. A high concentration of heat-inactivated human serum allowed the best proliferation of the used species. Therefore we further investigated these biofilms by analysing their structure by confocal laser scanning microscopy following fluorescence in situ hybridisation. The species showed mutual interactions as expected from other studies. The abundances of all organisms present in this model were determined by microscopic counting following species-specific identification by both fluorescence in situ hybridisation and immunofluorescence. The newly integrated treponemes were the most abundant organisms.

Conclusions

The use of 50% of heat-inactivated human serum used in the improved growth medium resulted in significantly thicker and more stable biofilms, and the quantitative representation of the used species represents the in vivo community of periodontitis patients much closer than in biofilms grown in the two media with less or no human serum. The appearance of T. denticola, P. gingivalis, and T. forsythia in the top layer of the biofilms, and the high abundance of T. denticola, reflects well the microbial situation observed at diseased sites. The improved model biofilms will allow further investigations of interactions between individual species and of the effects of atmospheric or nutritional changes, as well as interactions with tissue cells.

Probiotic Lactobacillus reuteri strains ATCC PTA 5289 and ATCC 55730 differ in their cariogenic properties in vitro

OBJECTIVE

The effects of probiotics on cariogenic biofilms remain controversial. Our aim was to characterise two probiotic Lactobacillus reuteri strains, ATCC PTA 5289 and ATCC 55730 from a cariogenic standpoint in vitro. These strains are used in commercial products designed for oral health purposes.

DESIGN

The adhesion and biofilm formation were studied on saliva-coated hydroxyapatite. The effects of glucose or sucrose on the biofilm formation were also tested. Arginine metabolism was assessed by measuring the pH in the presence of glucose and arginine. The degradation of hydroxyapatite was measured in three different growth media. Streptococcus mutans strains Ingbritt and MT 8148 were used as positive controls for bacterial adhesion and degradation of hydroxyapatite.

RESULTS

Strain ATCC PTA 5289 adhered on saliva-coated hydroxyapatite and formed detectable biofilm, but strain ATCC 55730 was poor in both adhesion and biofilm formation. Both strains were arginolytic and raised the pH in the presence of arginine. The amount of dissolved calcium from hydroxyapatite correlated with bacterial growth rate and the final pH of the growth medium.

CONCLUSION

L. reuteri strains ATCC PTA 5289 and ATCC 55730 differed in their adhesion, biofilm formation and arginine metabolism in vitro. Thus, these probiotic lactobacilli are likely to differ in their behaviour and cariogenic potential also in an oral environment.

The phylum Synergistetes in gingivitis and necrotizing ulcerative gingivitis

The clinical manifestation of necrotizing ulcerative gingivitis (NUG) is distinct from that of common gingivitis in that it is characterized by local necrosis of the gingival tissues, rapid onset, pain and extensive bleeding. The phylum Synergistetes is a novel bacterial phylum consisting of Gram-negative anaerobes, with evidence of presence in biofilms associated with periodontal and endodontic infections. To date, the involvement of members of this phylum in NUG has not been investigated. This study aimed to evaluate the presence and levels of known human oral Synergistetes bacterial clusters in dental plaque from patients with NUG and compare them with those found in gingivitis. Marginal dental plaque samples from 21 NUG and 21 gingivitis patients were analysed quantitatively by fluorescent in situ hybridization and microscopy for members of two oral Synergistetes clusters (A and B) and for Jonquetella anthropi. Synergistetes cluster A bacteria were detected in all samples but at higher levels (9.4-fold) and proportions (2.5-fold) in NUG patients than in gingivitis patients. However, with regard to Synergistetes cluster B bacteria, there were no differences between NUG and gingivitis patients. J. anthropi was detected in only half of the samples and at lower levels than the other taxa. In conclusion, these data demonstrate that Synergistetes cluster A bacteria, but not cluster B bacteria or J. anthropi, are more strongly associated with NUG than with gingivitis.

Down-regulation of NLRP3 inflammasome in gingival fibroblasts by subgingival biofilms: involvement of Porphyromonas gingivalis

Recognition of pathogen-associated molecular patterns that activate IL-1β is regulated by inflammasomes, predominantly of the nucleotide-binding oligomerization domain-like receptor (NLR) family. NLRP3 inflammasome is involved in the innate immune responses in periodontal disease. This is an inflammatory condition that destroys the tooth-supporting (periodontal) tissues, initiated by the subgingival formation of multi-species biofilms, frequently including the Gram-negative species Porphyromonas gingivalis. The aim of this study was to investigate the relative effect of P. gingivalis as part of subgingival biofilm, on the expressions of NLRP3 inflammasome, absent in melanoma (AIM)2 (a non-NLR inflammsome) and IL-1β by human gingival fibroblasts. The 10-species subgingival biofilm model, or its 9-species variant excluding P. gingivalis, were used to challenge the cells for 6 h. Gene expression analysis for various inflammasome components and IL-1β was performed by TaqMan real-time PCR. The 10-species subgingival biofilm reduced NLRP3 and IL-1β, but did not affect AIM2 expression. Exclusion of P. gingivalis from the biofilm partially rescued NLRP3 and IL-1β expressions. In conclusion, subgingival biofilms down-regulate NLRP3 and IL-1β expression, partly because of P. gingivalis. These dampened host innate immune responses may favour the survival and persistence of the associated biofilm species in the periodontal tissues.