Dental plaque as a microbial biofilm

Biochemical characterization of a recombinant Lactobacillus acidophilus strain expressing exogenous FomA protein

In previous research, to combine the immunogenicity of Fusobacterium nucleatum (F. nucleatum) and the probiotic properties of Lactobacillus acidophilus (L. acidophilus), we constructed a FomA-expressing L. acidophilus strain and assessed its immunogenicity. Our findings indicated that oral administration of the recombinant L. acidophilus strain reduced the risk of periodontal infection by Porphyromonas gingivalis (P. gingivalis) and F. nucleatum. However, because the exogenous FomA is an heterologous protein for the original bacterium, in this study, we assessed whether the biochemical characteristics of the recombinant L. acidophilus strain change due to the expression of the exogenous FomA protein.

OBJECTIVES

To test the biochemical characteristics of a recombinant L. acidophilus strain expressing exogenous FomA and assess its antibiotic sensitivity.

DESIGNS

We assessed the colony morphology, growth, acid production, and carbohydrate fermentation abilities of the recombinant L. acidophilus strain. In addition, we tested the adhesive ability and antimicrobial activity of the recombinant and assessed its antibiotic sensitivity through a drug susceptibility test.

RESULTS

The experimental results showed that the colony and microscopic morphology of the recombinant L. acidophilus strain was consistent with the original strain, and the recombinant strain grew well when cultured under aerobic or anaerobic conditions, exhibiting a growth rate that was identical to that of the standard strain. Similarly, the supernatants of the recombinant L. acidophilus can inhibit the growth of E. coli and P. gingivalis at different concentrations, and the recombinant strain displayed essentially the same drug sensitivity profile as the original L. acidophilus. However, to our surprise, the recombinant strains exhibited a greater adhesion ability than the reference strain.

CONCLUSIONS

Our study demonstrated that, in addition to an increased adhesion ability, the recombinant L. acidophilus strain maintained the basic characteristics of the standard strain ATCC 4356, including antibiotic sensitivity. Thus, the recombinant strains have great potential to be utilized as a safe and effective periodontitis vaccine in the future.

Caries and Periodontitis: Contesting the Conventional Wisdom on Their Aetiology

We review the literature on the oral microbiome and the role of the microbiota in the development of dental caries and periodontitis. While most research has been focused on identifying one or more specific determinants of these diseases, the results have provided limited predictive value and have not been able to explain the variation in the distribution of these diseases observed in epidemiological or clinical studies. Drawing on existing knowledge about the nature of the oral microbiota, we suggest that a stochastic model based on the Weiner process provides simple and parsimonious explanations for the pathogenesis of both caries and periodontitis, making few assumptions, and providing explanations for phenomena that have hitherto proved difficult, or have required complex arguments, to explain. These diseases occur as the result of the dental hard tissues and periodontal tissues integrating the random "noise" caused by normal metabolic activities of commensal microorganisms in the dental biofilm. The processes that result in the progression and regression of caries and periodontitis may be considered as "natural," rather than pathological, even if, when left unchecked over long periods of time, they can result in the development of pathologies. The likelihood of progression or regression can be influenced by other determinants, but these processes will nevertheless occur in the absence of such influences. The distributional characteristics of the model approximate the findings of epidemiological studies indicating that, for both caries and periodontitis, there will be few sites affected in the early period after the eruption of the permanent dentition, but in those older there is an almost linear relationship with increasing age; furthermore, the longer a site survives without being affected, the less likely that it will be affected. We discuss the clinical and public health importance of these findings.

Difference in virulence and composition of a cariogenic biofilm according to substratum direction

The aim of this study was to investigate the difference in composition and virulence of Streptococcus mutans biofilms according to substratum direction. S. mutans biofilms (46-h-old) were formed on three different saliva-coated hydroxyapatite (sHA) disc direction groups: downward (discs placed in the direction of gravity), vertical (discs placed parallel to gravity direction), and upward (discs placed opposite to gravity). The 46-h-old biofilms on sHA discs in the upward direction showed the highest biofilm accumulation, colony forming unit (CFU) count, and extracellular polysaccharide (EPS) amount, followed by those in the vertical and downward directions. In the confocal laser scanning microscopy (CLSM) study, the biofilms in the upward direction also showed the highest bacterial count (live or dead cells) and EPS biovolume. Scanning electron microscopy (SEM) analysis confirmed the microbiological and biochemical results. In addition, biofilm density and acid production were higher in the upward direction than those in the other directions. Our findings suggest that substratum direction, which might be related to gravity, strongly influences the formation and virulence of cariogenic biofilms and subsequent initiation of dental caries. Collectively, the differences in the formation and virulence of cariogenic biofilms are related to the direction of tooth surface (occlusal surfaces of mandibular teeth > proximal surfaces > occlusal surfaces of maxillary teeth).

Trend Analysis of Studies on Water Fluoridation Related to Dental Caries in PubMed

Water fluoridation has been cited as one of the top 10 public health achievements of the 20th century. Herein, we analyzed water fluoridation articles related to dental caries published in PubMed between 1950 and 2016 using informetrics and linguistic methods to investigate trends in the studies. To this aim, queries such as "dental caries and (water fluoridation or fluoridated water)," "dental caries and (fluoride or fluoridation)," and "dental caries" were submitted to PubMed to retrieve information about articles on water fluoridation within the area of dental caries and fluoride - their titles, abstracts, publication dates, author affiliations, and publication journals. This article information was then collected by an automatic web crawler and examined through informetrics and linguistic analyses. It was found that the number of articles concerned with water fluoridation and dental caries was 3,381 and declined over time after 1970. The articles were published by 750 journals - most notably, Community Dentistry and Oral Epidemiology and Caries Research. With regard to the geographic distribution of the authors, Europe and North America, especially the USA and UK, accounted for 59.9% of the articles published during the years 1987 to 2015, though there was a sharp increase in the number of authors in Oceania and Asia in recent years. In the titles and abstracts of the articles, "community" and "fluorosis" were mentioned more frequently than the other key terms selected in this study, regardless of the period examined. Our findings may allow one to assess how the research on water fluoridation has evolved over the past several decades.

Phenalen-1-One-Mediated Antimicrobial Photodynamic Therapy and Chlorhexidine Applied to a Novel Caries Biofilm Model

Antimicrobial photodynamic therapy (aPDT) may be useful as a supportive antimicrobial measure for caries-active subjects. In this study, the antimicrobial efficacy of aPDT with a phenalen-1-one photosensitizer was evaluated in a novel in vitro biofilm model comprising Actinomyces naeslundii, Actinomyces odontolyticus, and Streptococcus mutans and was compared to chlorhexidine. The proposed biofilm model allows high-throughput screening for antimicrobial efficacy while exhibiting a differentiated response to different antimicrobial approaches. While chlorhexidine 0.2% showed a reduction of ≈4 log10 for all species, aPDT led to a more pronounced reduction of S. mutans (2.8 log10) than of Actinomyces spp. (1.2 or 1.3 log10). A similar effect was also observed in monospecies biofilms. Therefore, aPDT may be more effective against S. mutans than against Actinomyces spp. when in biofilms, and this antimicrobial approach merits further investigations.

The Role of Oral Cavity Biofilm on Metallic Biomaterial Surface Destruction-Corrosion and Friction Aspects

Metallic biomaterials in the oral cavity are exposed to many factors such as saliva, bacterial microflora, food, temperature fluctuations, and mechanical forces. Extreme conditions present in the oral cavity affect biomaterial exploitation and significantly reduce its biofunctionality, limiting the time of exploitation stability. We mainly refer to friction, corrosion, and biocorrosion processes. Saliva plays an important role and is responsible for lubrication and biofilm formation as a transporter of nutrients for microorganisms. The presence of metallic elements in the oral cavity may lead to the formation of electro-galvanic cells and, as a result, may induce corrosion. Transitional microorganisms such as sulfate-reducing bacteria may also be present among the metabolic microflora in the oral cavity, which can induce biological corrosion. Microorganisms that form a biofilm locally change the conditions on the surface of biomaterials and contribute to the intensification of the biocorrosion processes. These processes may enhance allergy to metals, inflammation, or cancer development. On the other hand, the presence of saliva and biofilm may significantly reduce friction and wear on enamel as well as on biomaterials. This work summarizes data on the influence of saliva and oral biofilms on the destruction of metallic biomaterials.

Electrochemical Detection of Small Molecule Induced Pseudomonas aeruginosa Biofilm Dispersion

A simple electrochemical assay to monitor the dispersion of Pseudomonas aeruginosa PA01 biofilm is described. Pyrolytic graphite (PG) electrodes were modified with P. aeruginosa PA01 using layer-by-layer (LbL) methods. The presence of the bacteria on the electrodes was directly monitored using square wave voltammetry (SWV) via the electrochemical reduction of electroactive phenazine compounds expressed by the bacteria, which indicate the presence of biofilm. Upon treatment of bacteria-modified electrodes with a 2-aminoimidazole (2-AI) derivative with known Pseudomonas anti-biofilm properties, the bacteria-related electrochemical reduction peaks decreased in a concentration dependent manner, indicating dispersal of the biofilm on the electrode surface. A similar 2-AI compound with negligible anti-biofilm activity was used as a comparative control and produced muted electrochemical results. Electrochemical responses mirrored previously established bioassay-derived half maximal inhibition concentration (IC₅₀) and half maximal effective concentration (EC₅₀) values.. Biofilm dispersal detection via the electrochemical response was validated by monitoring crystal violet absorbance after its release from electrode confined P. aeruginosa biofilm. Mass spectrometry data showing multiple redox active phenazine compounds are presented to provide insight into the surface reaction complexity. Overall, we present a very simple assay to monitor the anti-biofilm activity of compounds of interest.

Anti-biofilm and remineralization effects of chitosan hydrogel containing amelogenin-derived peptide on initial caries lesions

In this study, we have designed a more clinically powerful anti-caries treatment by applying the amelogenin-derived peptide QP5 to the antibacterial carrier material chitosan in a hydrogel (CS-QP5 hydrogel), and characterized its effects on the inhibition of a cariogenic biofilm and the promotion of the remineralization of the initial caries lesions. The results indicated that the CS-QP5 hydrogel sustainably inhibited the growth of the Streptococcus mutans biofilm, lactic acid production and the metabolic activity over a prolonged period of time. Moreover, the CS-QP5 hydrogel promoted the remineralization of early enamel lesions, which were indicated by surface micro-hardness (, polarized light microscopy and transverse microradiography. In conclusion, the CS-QP5 hydrogel shows good potential for caries control in the clinic because of its antibacterial effects as well as the remineralization of initial enamel carious lesions even in a biofilm model over a prolonged period of time.

Influence of Helicobacter pylori culture supernatant on the ecological balance of a dual-species oral biofilm

Dental caries is a chronic progressive disease occurring in the tooth hard tissue due to multiple factors, in which bacteria are the initial cause. Both Streptococcus mutans and Streptococcus sanguinis are main members of oral biofilm. Helicobacter pylori may also be detected in dental plaque, playing an important role in the development of dental caries.

OBJECTIVE

The aim of this study was to investigate the effect of H. pylori culture supernatant on S. mutans and S. sanguinis dual-species biofilm and to evaluate its potential ability on affecting dental health.

MATERIAL AND METHODS

The effect of H. pylori supernatant on single-species and dual-species biofilm was measured by colony forming units counting and fluorescence in situ hybridization (FISH) assay, respectively. The effect of H. pylori supernatant on S. mutans and S. sanguinis extracellular polysaccharides (EPS) production was measured by both confocal laser scanning microscopy observation and anthrone-sulfuric acid method. The effect of H. pylori supernatant on S. mutans gene expression was measured by quantitative real-time PCR (qRT-PCR) assays.

RESULTS

H. pylori supernatant could inhibit both S. mutans and S. sanguinis biofilm formation and EPS production. S. sanguinis inhibition rate was significantly higher than that of S. mutans. Finally, S. mutans bacteriocin and acidogenicity related genes expression were affected by H. pylori culture supernatant.

CONCLUSION

Our results showed that H. pylori could destroy the balance between S. mutans and S. sanguinis in oral biofilm, creating an advantageous environment for S. mutans, which became the dominant bacteria, promoting the formation and development of dental caries.

Kinetics of calcium binding to dental biofilm bacteria

Dental biofilm bacteria can bind calcium ions and release them during a pH drop, which could decrease the driving force for dental demineralization (i.e. hydroxyapatite dissolution) occurring at reduced pHs. However, the kinetics of this binding and release is not completely understood. Here we validated a method to evaluate the kinetics of calcium binding and release to/from Streptococcus mutans, and estimated the importance of this reservoir as a source of ions. The kinetics of calcium binding was assessed by measuring the amount of bound calcium in S. mutans Ingbrit 1600 pellets treated with PIPES buffer, pH 7.0, containing 1 or 10 mM Ca; for the release kinetics, bacterial pellets previously treated with 1 mM or 10 mM Ca were exposed to the calcium-free or 1 mM Ca PIPES buffer, pH 7.0, for up to 60 min. Binding and release curves were constructed and parameters of kinetics were calculated. Also, calcium release was assessed by exposing pellets previously treated with calcium to a pH 5.0 buffer for 10 min. Calcium binding to bacteria was concentration-dependent and rapid, with maximum binding reached at 5 min. On the other hand, calcium release was slower, and according to the calculations, would never be complete in the groups pretreated with 10 mM Ca. Decreasing pH from 7.0 to 5.0 caused a release of calcium able to increase the surrounding fluid calcium concentration in 2 mM. The results suggest that dental biofilm bacteria may act as a calcium reservoir, rapidly binding ions from surrounding fluids, releasing them slowly at neutral pH and promptly during a pH drop.

Denture-associated biofilm infection in three-dimensional oral mucosal tissue models

Purpose

In vitro analyses of virulence, pathogenicity and associated host cell responses are important components in the study of biofilm infections. The Candida-related infection, denture-associated oral candidosis, affects up to 60 % of denture wearers and manifests as inflammation of palatal tissues contacting the denture-fitting surface. Commercially available three-dimensional tissue models can be used to study infection, but their use is limited for many academic research institutions, primarily because of the substantial purchase costs. The aim of this study was to develop and evaluate the use of in vitro tissue models to assess infections by biofilms on acrylic surfaces through tissue damage and Candida albicans virulence gene expression.

Methodology

In vitro models were compared against commercially available tissue equivalents (keratinocyte-only, SkinEthic; full-thickness, MatTek Corporation). An in vitro keratinocyte-only tissue was produced using a cancer-derived cell line, TR146, and a full-thickness model incorporating primary fibroblasts and immortalised normal oral keratinocytes was also generated. The in vitro full-thickness tissues incorporated keratinocytes and fibroblasts, and have potential for future further development and analysis.

Results

Following polymicrobial infection with biofilms on acrylic surfaces, both in-house developed models were shown to provide equivalent results to the SkinEthic and MatTek models in terms of tissue damage: a significant (P<0.05) increase in LDH activity for mixed species biofilms compared to uninfected control, and no significant difference (P>0.05) in the expression of most C. albicans virulence genes when comparing tissue models of the same type.

Conclusion

Our results confirm the feasibility and suitability of using these alternative in vitro tissue models for such analyses.

Red fluorescence of dental biofilm as an indicator for assessing the efficacy of antimicrobials

The study aimed to determine whether the red fluorescence (RF) of a dental microcosm biofilm as measured with quantitative light-induced fluorescence (QLF) technology is useful for assessing the efficacy of antimicrobials. Dental microcosm biofilms were formed on bovine enamel discs and grown under 0.3% sucrose challenge and treated with chlorhexidine (CHX) solutions at different concentrations (0.05%, 0.1%, and 0.5%) plus a negative control [sterile distilled water (DW)] twice daily for 7 days. The biofilms were photographed using a QLF-digital system to evaluate the RF by calculating the red/green ratio, and pH values of the medium were measured daily. After 7 days, the bacterial viability of the biofilm was assessed by measuring the counts of viable total bacteria and aciduric bacteria, and the percentage surface microhardness changes (%SHC) was evaluated. The RF and cariogenic properties were compared for the different concentrations of CHX, and their correlations were examined. The RF and its increase rate were much lower for CHX-treated biofilms than for DW-treated biofilms. The RF after 7 days of maturation decreased significantly with increasing CHX concentrations (p<0.001) and was from 31% (for 0.05% CHX) to 46% (for 0.5% CHX) lower than that of the DW group. Strong correlations were reported between the RF of the 7-day-maturation biofilms and cariogenic properties, such as the number of total bacteria (r=0.93), number of aciduric bacteria (r=0.97), supernatant pH (r=0.43), and %SHC (r=0.98). In conclusion, the RF of dental biofilms as measured with QLF technology can be used to nondestructively assess and monitor the effect of antimicrobials against biofilm.

The implication of probiotics in the prevention of dental caries

The current oral health crisis, whose causes are varied and complex, necessitates timely oral evaluation and early detection and treatment of oral health problems. Dramatic changes in eating habits and lifestyles are associated with the recent decline in oral health. Probiotics are "good" bacteria that support digestion and a healthy immune system and offer various health benefits to the host. Traditionally, probiotics have been used to improve gut health; the most common uses have historically been as a treatment or prevention of gastrointestinal infections and disease. During the last decade, studies have additionally suggested the intake of probiotics for oral health purposes. Probiotic use provides an effective strategy to combat oral disease, including the development of dental caries and periodontal infection. The aim of this review is to describe the beneficial roles of probiotic bacteria in the oral cavity and the potential mechanisms by which these bacteria exert their effects on oral health.

Infectious crystalline keratopathy

Infectious crystalline keratopathy was first reported by Gorovoy and colleagues in 1983 when they identified bacteria colonizing a cornea after a penetrating keratoplasty. Subsequent cases have elaborated on the organisms responsible and the management outcomes. Patients present with a white or gray branching opacity originating from an epithelial defect, commonly after a penetrating keratoplasty. Local immunosuppression contributes to the quiescent nature and the limited inflammatory response associated with infectious crystalline keratopathy. Diagnosis of the infective pathogens may be difficult, with a corneal scraping often being too superficial to obtain an adequate specimen. A biofilm is present that advantages microorganism survival, reduces antibiotic bioavailability, and inhibits diagnostic microbial detection. Treatment begins with topical antimicrobials, initially broad spectrum and then targeted to microorganism sensitivity. Adjunctive therapies to enhance the efficacy of treatment include disruption of the microorganism biofilm by laser, intrastromal antibiotics, and keratectomy. In recalcitrant cases, or where corneal scarring ensues, corneal transplantation is required.

Antimicrobial and Antibiofilm Effects of Human Amniotic/Chorionic Membrane Extract on Streptococcus pneumoniae

Background:Streptococcus pneumoniae colonize the human nasopharynx in the form of biofilms. The biofilms act as bacterial reservoirs and planktonic bacteria from these biofilms can migrate to other sterile anatomical sites to cause pneumonia, otitis media (OM), bacteremia and meningitis. Human amniotic membrane contains numerous growth factors and antimicrobial activity; however, these have not been studied in detail. In this study, we prepared amniotic membrane extract and chorionic membrane extract (AME/CME) and evaluated their antibacterial and antibiofilm activities against S. pneumoniae using an in vitro biofilm model and in vivo OM rat model.

Materials and Methods: The AME/CME were prepared and protein was quantified using DC^TM (detergent compatible) method. The minimum inhibitory concentrations were determined using broth dilution method, and the synergistic effect of AME/CME with Penicillin-streptomycin was detected checkerboard. The in vitro biofilm and in vivo colonization of S. pneumoniae were studied using microtiter plate assay and OM rat model, respectively. The AME/CME-treated biofilms were examined using scanning electron microscope and confocal microscopy. To examine the constituents of AME/CME, we determined the proteins and peptides of AME/CME using tandem mass tag-based quantitative mass spectrometry.

Results: AME/CME treatment significantly (p < 0.05) inhibited S. pneumoniae growth in planktonic form and in biofilms. Combined application of AME/CME and Penicillin-streptomycin solution had a synergistic effect against S. pneumoniae. Biofilms grown with AME/CME were thin, scattered, and unorganized. AME/CME effectively eradicated pre-established pneumococci biofilms and has a bactericidal effect. AME treatment significantly (p < 0.05) reduced bacterial colonization in the rat middle ear. The proteomics analysis revealed that the AME/CME contains hydrolase, ribonuclease, protease, and other antimicrobial proteins and peptides.

Conclusion: AME/CME inhibits S. pneumoniae growth in the planktonic and biofilm states via its antimicrobial proteins and peptides. AME/CME are non-cytotoxic, natural human product; therefore, they may be used alone or with antibiotics to treat S. pneumoniae infections.

Fluid-driven interfacial instabilities and turbulence in bacterial biofilms

Biofilms are thin layers of bacteria embedded within a slime matrix that live on surfaces. They are ubiquitous in nature and responsible for many medical and dental infections, industrial fouling and are also evident in ancient fossils. A biofilm structure is shaped by growth, detachment and response to mechanical forces acting on them. The main contribution to biofilm versatility in response to physical forces is the matrix that provides a platform for the bacteria to grow. The interaction between biofilm structure and hydrodynamics remains a fundamental question concerning biofilm dynamics. Here, we document the appearance of ripples and wrinkles in biofilms grown from three species of bacteria when subjected to high-velocity fluid flows. Linear stability analysis suggested that the ripples were Kelvin-Helmholtz Instabilities. The analysis also predicted a strong dependence of the instability formation on biofilm viscosity explaining the different surface corrugations observed. Turbulence through Kelvin-Helmholtz instabilities occurring at the interface demonstrated that the biofilm flows like a viscous liquid under high flow velocities applied within milliseconds. Biofilm fluid-like behavior may have important implications for our understanding of how fluid flow influences biofilm biology since turbulence will likely disrupt metabolite and signal gradients as well as community stratification.

Full validation of a method for the determination of drugs of abuse in non-mineralized dental biofilm using liquid chromatography-tandem mass spectrometry and application to postmortem samples

Alternative matrices play a major role in postmortem forensic toxicology, especially if common matrices (like body fluids or hair) are not available. Incorporation of illicit and medicinal drugs into non-mineralized dental biofilm (plaque) seems likely but has not been investigated so far. Analysis of plaque could therefore extend the spectrum of potentially used matrices in postmortem toxicology. For this reason, a rapid, simple and sensitive method for the extraction, determination and quantification of ten drugs of abuse from plaque using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and fully validated. Amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxy-N-ethylamphetamine (MDEA), 3,4-methylenedioxyamphetamine (MDA), cocaine, benzoylecgonine, morphine, codeine and 6-acetylmorphine were extracted from 2mg of dried and powdered plaque via ultrasonication with acetonitrile. The extracts were analyzed on a triple-quadrupole linear ion trap mass spectrometer in scheduled multiple reaction monitoring mode (sMRM). The method was fully validated and proved accurate, precise, selective and specific with satisfactory linearity within the calibrated ranges. The lower limit of quantification was 10-15pgmg^-1 for all compounds except for MDA (100pgmg^-1) and amphetamine (200pgmg^-1). The method has been successfully applied to three authentic postmortem samples with known drug history. Amphetamine, MDMA, cocaine, benzoylecgonine, morphine and codeine could be detected in these cases in concentrations ranging from 18pgmg^-1 for cocaine to 1400pgmg^-1 for amphetamine.

Biofilms in Endodontics-Current Status and Future Directions

Microbiota are found in highly organized and complex entities, known as biofilms, the characteristics of which are fundamentally different from microbes in planktonic suspensions. Root canal infections are biofilm mediated. The complexity and variability of the root canal system, together with the multi-species nature of biofilms, make disinfection of this system extremely challenging. Microbial persistence appears to be the most important factor for failure of root canal treatment and this could further have an impact on pain and quality of life. Biofilm removal is accomplished by a chemo-mechanical process, using specific instruments and disinfecting chemicals in the form of irrigants and/or intracanal medicaments. Endodontic research has focused on the characterization of root canal biofilms and the clinical methods to disrupt the biofilms in addition to achieving microbial killing. In this narrative review, we discuss the role of microbial biofilms in endodontics and review the literature on the role of root canal disinfectants and disinfectant-activating methods on biofilm removal.

In silico search of inhibitors of Streptococcus mutans for the control of dental plaque

Biofilm is an extremely complex microbial community arranged in a matrix of polysaccharides and attached to a substrate. Its development is crucial in the pathophysiology of oral infections like dental caries, as well as in periodontal, pulp, and periapical diseases. Streptococcus mutans is one of the most effective microorganisms in lactic acid production of the dental biofilm. Identifying essential Streptococcus mutans proteins using bioinformatics methods helps to search for alternative therapies. To this end, the bacterial genomes of several Streptococcus mutans strains and representative strains of other cariogenic and non-cariogenic bacteria were analysed by identifying pathogenicity islands and alignments with other bacteria, and by detecting the exclusive genes of cariogenic species in comparison to the non-pathogenic ones. This study used tools for orthology prediction such as BLAST and OrthoMCL, as well as the server IslandViewer for the detection of pathogenicity islands. In addition, the potential interactome of Streptococcus mutans was rebuilt by comparing it to interologues of other species phylogenetically close to or associated with cariogenicity. This protocol yielded a final list of 20 proteins related to potentially virulent factors that can be used as therapeutic targets in future analyses. The EIIA and EIIC enzymatic subunits of the phosphotransferase system (PTS) were prioritized, as well as the pyruvate kinase enzyme, which are directly involved in the metabolism of carbohydrates and in obtaining the necessary energy for the microorganism's survival. These results will guide a subsequent experimental trial to develop new, safe, and effective molecules in the treatment of dental caries.

Suppression of αvβ6 Integrin Expression by Polymicrobial Oral Biofilms in Gingival Epithelial Cells

Periodontal diseases manifest by the formation of deep pockets between the gingiva and teeth where multispecies bacterial biofilms flourish, causing inflammation and bone loss. Epithelial cell receptor αvβ6 integrin that regulates inflammation by activating the anti-inflammatory cytokine transforming growth factor-β1, is highly expressed in healthy junctional epithelium that connects the gingiva to the tooth enamel. However, its expression is attenuated in human periodontal disease. Moreover, Itgb6^−/− mice display increased periodontal inflammation compared to wild-type mice. We hypothesized that bacterial biofilms present in the periodontal pockets suppress αvβ6 integrin levels in periodontal disease and that this change aggravates inflammation. To this end, we generated three-week-old multi-species oral biofilms in vitro and treated cultured gingival epithelial cells (GECs) with their extracts. The biofilm extracts caused suppression of β6 integrin expression and upregulation of pro-inflammatory cytokines, including interleukin-1β and -6. Furthermore, GECs with β6 integrin siRNA knockdown showed increased interleukin-1β expression, indicating that αvβ6 integrin-deficiency is associated with pro-inflammatory cytokine responsiveness. FSL-1, a synthetic bacterial lipopeptide, also suppressed β6 integrin expression in GECs. Therefore, biofilm components, including lipopeptides, may downregulate αvβ6 integrin expression in the pocket epithelium and thus promote epithelial cell-driven pro-inflammatory response in periodontal disease.

A novel antimicrobial peptide against dental-caries-associated bacteria

Dental caries, a highly prevalent oral disease, is primarily caused by pathogenic bacteria infection, and most of them are anaerobic. Herein, we investigated the activity of a designed antimicrobial peptide ZXR-2, and found it showed broad-spectrum activity against a variety of Gram-positive and Gram-negative oral bacteria, particularly the caries-related taxa Streptococcus mutans. Time-course killing assays indicated that ZXR-2 killed most bacterial cells within 5 min at 4 × MIC. The mechanism of ZXR-2 involved disruption of cell membranes, as observed by scanning electron microscopy. Moreover, ZXR-2 inhibited the formation of S. mutans biofilm, but showed limited hemolytic effect. Based on its potent antimicrobial activity, rapid killing, and inhibition of S. mutans biofilm formation, ZXR-2 represents a potential therapeutic for the prevention and treatment of dental caries.

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.

Determining the relationship between atherosclerosis and periodontopathogenic microorganisms in chronic periodontitis patients

OBJECTIVES

The aim of this study is to determine the relationship between atherosclerosis and periodontopathogenic microorganisms in chronic periodontitis patients following periodontal treatment.

MATERIALS AND METHODS

A total of 40 patients were included in the study. 20 of these patients diagnosed with atherosclerosis and chronic periodontitis formed the test group. The remaining 20 patients were systemically healthy patients diagnosed with chronic periodontitis and formed the control group. All patients had nonsurgical periodontal treatment. The periodontopathogenic microorganism levels were determined at baseline and at 6 months in microbial dental plaque samples and WBC, LDL, HDL, PLT, fibrinogen, creatinine and hs-CRP levels were determined by blood samples.

RESULTS

Statistically significant reduction has been achieved in clinical periodontal parameters following non-surgical periodontal treatment in test and control groups. Following periodontal treatment, WBC, LDL, PLT, fibrinogen, creatinine and hs-CRP levels significantly decreased and HDL levels significantly increased in both test and control groups. Similarly, the periodontopathogenic microorganism levels significantly decreased following periodontal treatment in the test and control groups. A statistically significant positive correlation has been determined between the periodontopathogenic microorganism levels and WBC, LDL, PLT, fibrinogen, creatinine, and hs-CRP levels in the test group.

CONCLUSIONS

The association between hs-CRP, WBC, LDL, PLT, fibrinogen, creatinine, and the amount of periodontopathogenic microorganisms indicates the possibility that periodontal treatment could decrease the risk atherosclerosis. More studies must be conducted in order for these results to be supported.

Exploring the oral microflora of preschool children

The oral cavity is one of the most important and complicated habitats in our body and supports diverse microbial communities. In this study, we aimed to determine the bacterial diversity and composition of various oral micro-niches. Samples were collected from supragingival plaque, saliva, and tongue coating from 10 preschool children (30 samples total). 16S rRNA gene pyrosequencing dataset generated 314,639 clean reads with an average of 10,488 ± 2,787 reads per sample. The phyla Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Fusobacteria were predominant, accounting for more than 90% of the total sequences. We found the highest α diversity, microbial richness, and evenness in plaque, compared with saliva and tongue coating. Plaque was also distinguished from saliva and tongue coating by phylogenetic distances (weighted UniFrac). Taxa with different relative abundances were further identified, confirming the existence of microbial differences across the three niches. Core microbiomes were defined of each niche; however, only a small proportion of operational taxonomic units (8.07%) were shared by the three niches. Coaggregation between Actinomyces spp. and Streptococcus spp. and other correlations among periodontal pathogens, such as Prevotella, Fusobacteria, Capnocytophaga, and Tannerella, were shown by a co-occurrence network. In summary, our study provides a framework of oral microbial communities in the population of preschool children as a baseline for further studies of oral diseases related to microbes.

Comparative gene expression analysis of Porphyromonas gingivalis ATCC 33277 in planktonic and biofilms states

Background and objective

Porphyromonas gingivalis is a keystone pathogen in the onset and progression of periodontitis. Its pathogenicity has been related to its presence and survival within the subgingival biofilm. The aim of the present study was to compare the genome-wide transcription activities of P. gingivalis in biofilm and in planktonic growth, using microarray technology.

Material and methods

P. gingivalis ATCC 33277 was incubated in multi-well culture plates at 37°C for 96 hours under anaerobic conditions using an in vitro static model to develop both the planktonic and biofilm states (the latter over sterile ceramic calcium hydroxyapatite discs). The biofilm development was monitored by Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM). After incubation, the bacterial cells were harvested and total RNA was extracted and purified. Three biological replicates for each cell state were independently hybridized for transcriptomic comparisons. A linear model was used for determining differentially expressed genes and reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to confirm differential expression. The filtering criteria of ≥ ±2 change in gene expression and significance p-values of <0.05 were selected.

Results

A total of 92 out of 1,909 genes (4.8%) were differentially expressed by P. gingivalis growing in biofilm compared to planktonic. The 54 up-regulated genes in biofilm growth were mainly related to cell envelope, transport, and binding or outer membranes proteins. Thirty-eight showed decreased expression, mainly genes related to transposases or oxidative stress.

Conclusion

The adaptive response of P. gingivalis in biofilm growth demonstrated a differential gene expression.

Normal Oral Flora and the Oral Ecosystem

The oral ecosystem comprises the oral flora, so-called oral microbiome, the different anatomic microniches of the oral cavity, and its bathing fluid, saliva. The oral microbiome comprises a group of organisms and includes bacteria, archaea, fungi, protozoa, and viruses. The oral microbiome exists suspended in saliva as planktonic phase organisms or attached to oral surfaces as a plaque biofilm. Homeostasis of the plaque biofilm and its symbiotic relationship with the host is critical for oral health. Disequilibrium or dysbiosis within the plaque biofilms is the initiating event that leads to major oral diseases, such as caries and periodontal disease.

Preparation and evaluation of PCLA2575 membranes loaded ornidazole in vitro

The aim of this study was to evaluate the properties of the sustained release and antibacterial activity of the ornidazole-drug-loaded membranes using poly[(ethylene glycol)-caprolactone-lactide] (PCLA2575) as membrane material. Ornidazole-loaded membranes were prepared by solvent casting method with the proportion of 5 wt%, 8 wt%, and 10 wt%, respectively. In vitro drug release properties were determined by ultraviolet spectrophotometric method. The antibacterial activities against Streptococcus mutans and Fusobacterium nucleatum in vitro were observed on solid culture medium. The membrane had the high drug loadings and slow-release performance. Drug release time was shortened with the increase in the content of ornidazole, but all of them can achieve more than 7 days. The membrane had strong inhibitory effect on both S. mutans and F. nucleatum. As drug content increased, the antibacterial activities also increased. The membrane had better inhibitory effect on F. nucleatum than S. mutans. Therefore, the ornidazole drug-loaded membrane is expected to be used for the treatment of periodontal disease because of the obvious effect of periodontal pathogens inhibition and good sustained-release performance.

A randomised clinical study to determine the effect of a toothpaste containing enzymes and proteins on plaque oral microbiome ecology

The numerous species that make up the oral microbiome are now understood to play a key role in establishment and maintenance of oral health. The ability to taxonomically identify community members at the species level is important to elucidating its diversity and association to health and disease. We report the overall ecological effects of using a toothpaste containing enzymes and proteins compared to a control toothpaste on the plaque microbiome. The results reported here demonstrate that a toothpaste containing enzymes and proteins can augment natural salivary defences to promote an overall community shift resulting in an increase in bacteria associated with gum health and a concomitant decrease in those associated with periodontal disease. Statistical analysis shows significant increases in 12 taxa associated with gum health including Neisseria spp. and a significant decrease in 10 taxa associated with periodontal disease including Treponema spp. The results demonstrate that a toothpaste containing enzymes and proteins can significantly shift the ecology of the oral microbiome (at species level) resulting in a community with a stronger association to health.

Balancing microbial and mammalian cell functions on calcium ion-modified implant surfaces

Implant integration is a complex process mediated by the interaction of the implant surface with the surrounding ions, proteins, bacteria, and tissue cells. Although most implants achieve long-term bone-tissue integration, preventing pervasive implant-centered infections demands further advances, particularly in surfaces design. In this work, we analyzed classical microrough implant surfaces (only acid etched, AE; sandblasted then acid etching, SB + AE) and a new calcium-ion-modified implant surface (AE + Ca) in terms of soft- and hard-tissue integration, bacterial adhesion, and biofilm formation. We cultured on the surfaces primary oral cells from gingiva and alveolar bone, and three representative bacterial strains of the oral cavity, emulating oral conditions of natural saliva and blood plasma. With respect to gingiva and bone cells and in the presence of platelets and plasma proteins, AE + Ca surfaces yielded in average 86% higher adhesion, 44% more proliferation, and triggered 246% more synthesis of extracellular matrix biomolecules than AE-unmodified controls. Concomitantly, AE + Ca surfaces regardless of conditioning with saliva and/or blood plasma showed significantly less bacterial adhesion (67% reduction in average) and biofilm formation (40% reduction in average) than unmodified surfaces. These results highlight the importance of a calcium-rich hydrated interface to favor mammalian cell functions over microbial colonization at implant surfaces. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 421-432, 2018.

Surface Coating of Gypsum-Based Molds for Maxillofacial Prosthetic Silicone Elastomeric Material: Evaluating Different Microbial Adhesion

PURPOSE

To compare the adhesion of three microorganisms on modified and unmodified silicone elastomer surfaces with different surface roughnesses and porosities.

MATERIALS AND METHODS

Candida albicans, Streptococcus mutans, and Staphylococcus aureus were incubated with modified and unmodified silicone groups (N = 35) for 30 days at 37°C. The counts of viable microorganisms in the accumulating biofilm layer were determined and converted to cfu/cm² unit surface area. A scanning electron microscope (SEM) was used to evaluate the microbial adhesion. Statistical analysis was performed using t-test, one-way ANOVA, and post hoc tests as indicated.

RESULTS

Significant differences in microbial adhesion were observed between modified and unmodified silicone elastomers after the cells were incubated for 30 days (p < 0.001). SEM showed evident differences in microbial adhesion on modified silicone elastomer compared with unmodified silicone elastomer.

CONCLUSIONS

Surface modification of silicone elastomer yielding a smoother and less porous surface showed lower adhesion of different microorganisms than observed on unmodified surfaces.

Potential applications of antimicrobial peptides and their mimics in combating caries and pulpal infections

Antimicrobial peptides (AMPs) are short cationic host-defense molecules that provide the early stage of protection against invading microbes. They also have important modulatory roles and act as a bridge between innate and acquired immunity. The types and functions of oral AMPs were reviewed and experimental reports on the use of natural AMPs and their synthetic mimics in caries and pulpal infections were discussed. Natural AMPs in the oral cavity, predominantly defensins, cathelicidins and histatins, possess antimicrobial activities against oral pathogens and biofilms. Incomplete debridement of microorganisms in root canal space may precipitate an exacerbated immune response that results in periradicular bone resorption. Because of their immunomodulatory and wound healing potentials, AMPs stimulate pro-inflammatory cytokine production, recruit host defense cells and regulate immuno-inflammatory responses in the vicinity of the pulp and periapex. Recent rapid advances in the development of synthetic AMP mimics offer exciting opportunities for new therapeutic initiatives in root canal treatment and regenerative endodontics.

STATEMENT OF SIGNIFICANCE

Identification of new therapeutic strategies to combat antibiotic-resistant pathogens and biofilm-associated infections continues to be one of the major challenges in modern medicine. Despite the presence of commercialization hurdles and scientific challenges, interests in using antimicrobial peptides as therapeutic alternatives and adjuvants to combat pathogenic biofilms have never been foreshortened. Not only do these cationic peptides possess rapid killing ability, their multi-modal mechanisms of action render them advantageous in targeting different biofilm sub-populations. These factors, together with adjunctive bioactive functions such as immunomodulation and wound healing enhancement, render AMPs or their synthetic mimics exciting candidates to be considered as adjuncts in the treatment of caries, infected pulps and root canals.

Development of Nano-Antimicrobial Biomaterials for Biomedical Applications

Around the globe, there is a great concern about controlling growth of pathogenic microorganisms for the prevention of infectious diseases. Moreover, the greater incidences of cross contamination and overuse of drugs has contributed towards the development of drug resistant microbial strains making conditions even worse. Hospital acquired infections pose one of the leading complications associated with implantation of any biomaterial after surgery and critical care. In this regard, developing non-conventional antimicrobial agents which would prevent the aforementioned causes is under the quest. The rapid development in nanoscience and nanotechnology has shown promising potential for developing novel biocidal agents that would integrate with a biomaterial to prevent bacterial colonization and biofilm formation. Metals with inherent antimicrobial properties such as silver, copper, zinc at nano scale constitute a special class of antimicrobials which have broad spectrum antimicrobial nature and pose minimum toxicity to humans. Hence, novel biomaterials that inhibit microbial growth would be of great significance to eliminate medical device/instruments associated infections. This chapter comprises the state-of-art advancements in the development of nano-antimicrobial biomaterials for biomedical applications. Several strategies have been targeted to satisfy few important concern such as enhanced long term antimicrobial activity and stability, minimize leaching of antimicrobial material and promote reuse. The proposed strategies to develop new hybrid antimicrobial biomaterials would offer a potent antibacterial solution in healthcare sector such as wound healing applications, tissue scaffolds, medical implants, surgical devices and instruments.

Enzymology and Ultrastructure of the in situ Pellicle in Caries-Active and Caries-Inactive Patients

Aim: The present study aimed to evaluate the impact of caries activity on the key enzymes and the ultrastructure of the in situ pellicle. Methods: Pellicle formation was performed on bovine enamel slabs. Intraoral exposure (3, 30, and 120 min) was accomplished by 14 caries-active (DMFS: 22.7 ± 12.1) and 13 caries-inactive (DMFS: 1.5 ± 1.8) individuals. The enzyme activities (lysozyme, peroxidase, α-amylase, glycosyltransferase [GTF]) in the in situ pellicle and resting saliva of all participants were analyzed directly after oral exposure. In addition, a simultaneous visualization of these enzymes, extracellular glucans, and adherent bacteria was carried out. Fluorescent patterns were analyzed with fluorescence labeling and 4′,6-diamidino-2-phenylindole/concanavalin A staining. In addition, the distribution of GTF B, C, and D and the ultrastructure of the pellicle were examined by gold immunolabeling and transmission electron microscopy with selected samples. Results: Enzyme activities of amylase, peroxidase, lysozyme, and GTF were detected on all enamel slabs in an active conformation. Neither exposure time nor caries activity had an impact on the enzyme activities. Gold immunolabeling indicated that the pellicle of caries-active subjects tends to more GTF D molecules. The pellicles of caries-inactive and -active individuals revealed a similar ultrastructural pattern. Conclusion: The enzyme activities as well as the pellicle's ultrastructure are of high similarity in caries-active and -inactive subjects. Thereby, oral exposure time has no significant influence. This reflects a high uniformity during the initial phase of bioadhesion (3-120 min) concerning enzymatic functions. However, there is a tendency towards more GTF D in caries-active individuals.

Bacteriostatic Effect of Simvastatin on Selected Oral Streptococci in Vitro

CONTEXT AND OBJECTIVE

Simvastatin is a widely used cholesterol-lowering drug, which has been found to have a number of pleiotropic effects. The aim of this study was to evaluate the antimicrobial effectiveness of simvastatin against selected oral streptococci as determined by the minimum inhibitory concentration (MIC).

METHODS

Streptococcus mutans, Streptococcus sanguis, Streptococcus anginosus, and Streptococcus salivarius were the test microorganisms. The serial dilution method was used to determine the MIC of simvastatin against these organisms. The MIC was defined as the lowest concentration of simvastatin that completely inhibited growth of the test organisms.

RESULTS

The data indicate that simvastatin inhibits the growth of the test organisms, with MIC's ranging from 7.8 to 15.6 μg/ml.

CONCLUSIONS

Simvastatin has MIC's against the selected bacteria that compare favorably with reported values for topical agents such as essential oil, chlorhexidine gluconate, and triclosan. The levels of simvastatin required to inhibit bacterial growth of oral bacteria exceed the reported levels of the drug found in plasma or crevicular fluid of patients who are treated with this cholesterol-lowering drug. However, clinical studies are warranted to investigate the potential use of simvastatin as a novel antiplaque agent that could be used in local drug delivery to the oral cavity of those patients who are prescribed this cholesterol-lowering drug.

Clotrimazole and econazole inhibit Streptococcus mutans biofilm and virulence in vitro

OBJECTIVE

The aim of this study was to determine the inhibitory effect of eight antifungal drugs on S. mutans growth, biofilm formation and virulence factors.

METHODS

The actions of antifungal drugs on S. mutans were determined by recovery plates and survival kinetic curves. Biofilms were observed by scanning electron microscopy and the viable cells were recovered on BHI plates, meanwhile biofilms were stained by BacLight live/dead kit to investigate the biofilm viability. Bacteria/extracellular polysaccharides staining assays were performed to determine the EPS production of S. mutans biofilms. Acidogenicity and acidurity of S. mutans were determined using pH drop and acid tolerance assays, and the expression of ldh gene was evaluated using qPCR.

RESULTS

We found that clotrimazole (CTR) and econazole (ECO) showed antibacterial activities on S. mutans UA159 and S. mutans clinical isolates at 12.5 and 25mg/L, respectively. CTR and ECO could also inhibit S. mutans biofilm formation and reduce the viability of preformed biofilm. CTR and ECO affected the live/dead ratio and the EPS/bacteria ratio of S. mutans biofilms. CTR and ECO also inhibited the pH drop, lactate acid production, and acid tolerance. The abilities of CTR and ECO to inhibit S. mutans ldh expression were also confirmed.

CONCLUSIONS

We found that two antifungal azoles, CTR and ECO, had the abilities to inhibit the growth and biofilm formation of S. mutans and more importantly, they could also inhibit the virulence factors of S. mutans.

Influence of fluoride on the bacterial composition of a dual-species biofilm composed of Streptococcus mutans and Streptococcus oralis

Despite the widespread use of fluoride for the prevention of dental caries, few studies have demonstrated the effects of fluoride on the bacterial composition of dental biofilms. This study investigated whether fluoride affects the proportion of Streptococcus mutans and S. oralis in mono- and dual-species biofilm models, via microbiological, biochemical, and confocal fluorescence microscope studies. Fluoride did not affect the bacterial count and bio-volume of S. mutans and S. oralis in mono-species biofilms, except for the 24-h-old S. mutans biofilms. However, fluoride reduced the proportion and bio-volume of S. mutans but did not decrease those of S. oralis during both S. oralis and S. mutans dual-species biofilm formation, which may be related to the decrease in extracellular polysaccharide formation by fluoride. These results suggest that fluoride may prevent the shift in the microbial proportion to cariogenic bacteria in dental biofilms, subsequently inhibiting the cariogenic bacteria dominant biofilm formation.

Sustained-release drug delivery of antimicrobials in controlling of supragingival oral biofilms

INTRODUCTION

Dental caries, a bacterial biofilm-associated disease, is a prevalent oral health problem. It is a bacterial biofilm-associated disease. Conventional means of combating this disease involves oral hygiene, mostly tooth brushing. Supplementary means of prevention and treatment is often necessary. The use of sustained-release delivery systems, locally applied to the oral cavity appears to be one of the most acceptable avenues for the delivery of antimicrobial agents. Area covered: The development and current approaches of local sustained delivery technologies applied to the oral cavity for treatment and prevention of dental caries is discussed. The use of polymeric drug delivery systems, varnishes, liposomes and nanoparticles is presented. Expert opinion: The use of local sustained-release delivery systems applied to the oral cavity has numerous clinical, pharmacological and toxicological advantages over conventional means. Various sustained-release technologies have been suggested over the course of several years. The current research on oral diseases concentrates predominantly on improving the drug delivery. With progress in pharmaceutical technology, sophisticated controlled-release platforms are being developed. The sustained release concept is innovative and there are few products available for the benefit of all populations. Harmonizing academic research with the dental industry will surely expedite the development and commercialization of more products of such pharmacological nature.

High-Velocity Microsprays Enhance Antimicrobial Activity in Streptococcus mutans Biofilms

Streptococcus mutans in dental plaque biofilms play a role in caries development. The biofilm's complex structure enhances the resistance to antimicrobial agents by limiting the transport of active agents inside the biofilm. The authors assessed the ability of high-velocity water microsprays to enhance delivery of antimicrobials into 3-d-old S. mutans biofilms. Biofilms were exposed to a 90° or 30° impact, first using a 1-µm tracer bead solution (10⁹ beads/mL) and, second, a 0.2% chlorhexidine (CHX) or 0.085% cetylpyridinium chloride (CPC) solution. For comparison, a 30-s diffusive transport and simulated mouthwash were also performed. Confocal microscopy was used to determine number and relative bead penetration depth into the biofilm. Assessment of antimicrobial penetration was determined by calculating the killing depth detected by live/dead viability staining. The authors first demonstrated that the microspray was able to deliver significantly more microbeads deeper in the biofilm compared with diffusion and mouthwashing exposures. Next, these experiments revealed that the microspray yielded better antimicrobial penetration evidenced by deeper killing inside the biofilm and a wider killing zone around the zone of clearance than diffusion alone. Interestingly the 30° impact in the distal position delivered approximately 16 times more microbeads and yielded approximately 20% more bacteria killing (for both CHX and CPC) than the 90° impact. These data suggest that high-velocity water microsprays can be used as an effective mechanism to deliver microparticles and antimicrobials inside S. mutans biofilms. High shear stresses generated at the biofilm-burst interface might have enhanced bead and antimicrobial delivery inside the remaining biofilm by combining forced advection into the biofilm matrix and physical restructuring of the biofilm itself. Further, the impact angle has potential to be optimized both for biofilm removal and active agents' delivery inside biofilm in those protected areas where some biofilm might remain.

Inhibitory effect for proliferation of oral bacteria in dogs by tooth brushing and application of toothpaste

To investigate inhibitory effect for oral bacterial proliferation, we divided 12 dogs into 3 groups; scaling alone (C; control group), brushing (B) and application of toothpaste (P). Before scaling (Pre) and at 0 to 8 weeks after scaling (0-8 w), we collected oral bacteria from the dental surface every week and counted them using a bacterial counter. The results demonstrated a significant reduction in the number of oral bacteria for group B relative to Pre and group C, as well as for group P relative to group C at 5-7 w. Consequently, brushing may inhibit an increase in the number of oral bacteria, and toothpaste may be effective at a certain level, although not more than that of brushing.

The antibacterial activity of chlorhexidine digluconate against Streptococcus mutans biofilms follows sigmoidal patterns

The aim of this study was to determine the pattern of the antibacterial activity of chlorhexidine digluconate (CHX) against mature Streptococcus mutans biofilms. Streptococcus mutans biofilms were formed on saliva-coated hydroxyapatite discs and then treated with 0-20% CHX, once, three times, or five times (1 min per treatment) during the period of mature biofilm formation (beyond 46 h). After the treatments, the colony-forming unit (CFU) counts of the treated biofilms were determined. The pH values of the spent culture medium were also determined to investigate the change in pH resulting from the antibacterial activity of CHX. The relationships between the concentration of CHX and the CFU counts and the concentration of CHX and culture medium pH, relative to the number of treatments performed, were evaluated using a sigmoidal curve-fitting procedure. The changes in CFU counts and culture medium pH followed sigmoidal curves and were dependent on the concentration of CHX (R² = 0.99). The sigmoidal curves were left-shifted with increasing number of treatments. Furthermore, the culture-medium pH of the treated biofilms increased as their CFU counts decreased. The lowest CHX concentration to increase culture-medium pH above the critical pH also decreased as the number of treatments increased. These results may provide fundamental information for selecting the appropriate CHX concentrations to treat S. mutans biofilms.