Deposition and retention of vital and dead Streptococcus sanguinis cells on glass surfaces in a flow-chamber system

Effect of Dentifrice Ingredients on Volume and Vitality of a Simulated Periodontal Multispecies Biofilm

The aim of this in vitro study was to investigate the effect of different toothpaste ingredients on biofilm volume and vitality in an established non-contact biofilm removal model. A multi-species biofilm comprising Porphyromonas gingivalis, Streptococcus sanguinis, and Fusobacterium nucleatum was grown on protein-coated titanium disks. Six disks per group were exposed to 4 seconds non-contact brushing using a sonic toothbrush. Four groups assessed slurries containing different ingredients, i.e., dexpanthenol (DP), peppermint oil (PO), cocamidopropyl betaine (CB), and sodium hydroxide (NaOH), one positive control group with the slurry of a toothpaste (POS), and a negative control group with physiological saline (NEG). Biofilm volume and vitality were measured using live-dead staining and confocal laser scanning microscopy. Statistical analysis comprised descriptive statistics and inter-group differences. In the test groups, lowest vitality and volume were found for CB (50.2 ± 11.9%) and PO (3.6 × 105 ± 1.8 × 105 µm3), respectively. Significant differences regarding biofilm vitality were found comparing CB and PO (p = 0.033), CB and NEG (p = 0.014), NaOH and NEG (p = 0.033), and POS and NEG (p = 0.037). However, no significant inter-group differences for biofilm volume were observed. These findings suggest that CB as a toothpaste ingredient had a considerable impact on biofilm vitality even in a non-contact brushing setting, while no considerable impact on biofilm volume was found.

Polymicrobial oral biofilm models: simplifying the complex

Over the past century, numerous studies have used oral biofilm models to investigate growth kinetics, biofilm formation, structure and composition, antimicrobial susceptibility and host-pathogen interactions. In vivo animal models provide useful models of some oral diseases; however, these are expensive and carry vast ethical implications. Oral biofilms grown or maintained in vitro offer a useful platform for certain studies and have the advantages of being inexpensive to establish and easy to reproduce and manipulate. In addition, a wide range of variables can be monitored and adjusted to mimic the dynamic environmental changes at different sites in the oral cavity, such as pH, temperature, salivary and gingival crevicular fluid flow rates, or microbial composition. This review provides a detailed insight for early-career oral science researchers into how the biofilm models used in oral research have progressed and improved over the years, their advantages and disadvantages, and how such systems have contributed to our current understanding of oral disease pathogenesis and aetiology.

Influence of the amplitude of different side-to-side toothbrushes on noncontact biofilm removal

OBJECTIVES

To investigate the impact of the lateral deflection of toothbrush bristles (amplitude) of three side-to-side toothbrushes for noncontact biofilm removal in an artificial interdental space model.

MATERIALS AND METHODS

A three-species biofilm (Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus sanguinis) was formed in vitro on protein-coated titanium disks. A flow chamber system was combined with a static biofilm growth model. The amplitudes of three commercial side-to-side toothbrushes were evaluated by means of a dose response analysis. The amplitudes were decreased in steps (100%, 85%, 70%, 55%, and 40%). Subsequently, the biofilm-coated substrates were exposed to the toothbrushes. The biofilms were analyzed with confocal laser scanning microscope images and measured using volumetric analyses.

RESULTS

The predictability of interdental biofilm reduction differed among the toothbrushes. A lower variety in the results of repeated experiments occurred in toothbrush C compared to toothbrushes A and B. Toothbrush C obtained highest percentage of biofilm reduction by 85% of amplitude power setting (median biofilm reduction 76%). Decreasing the amplitude from 85 to 40% resulted in reduced biofilm reduction (p = 0.029). In contrast, no significance could be observed for the differences of the tested amplitudes within toothbrushes A and B (p > 0.05). Between the toothbrushes, a significant difference in interdental biofilm reduction was found between C-A (p = 0.029) and C-B (p = 0.029) with amplitude of 85%.

CONCLUSIONS

The amplitude of one of the investigated side-to-side toothbrushes affected the biofilm reduction predictably in an interdental space model.

CLINICAL RELEVANCE

Within certain toothbrushes, a specific amplitude power setting may demonstrate beneficial effects on noncontact biofilm removal.

Effects of varying concentrations of sodium chloride and acidic conditions on the behavior of Vibrio parahaemolyticus and Vibrio vulnificus cold-starved in artificial sea water microcosms

There has been limited information available on the behavior of Vibrio parahaemolyticus and Vibrio vulnificus as a function of higher levels of NaCl in combination with acidic pH. In the present study, bacterial suspensions were transferred into artificial seawater (pH 4-7) microcosms containing 0.75% NaCl and supplemented with 5, 10, and 30% NaCl, respectively. Each of V. parahaemolyticus and V. vulnificus was inoculated in these microcosms and fermented seafood, and then stored at 4 °C until the microbial populations reached below the detectable levels on agar plates (thiosulphate-citrate-bile salts-sucrose agar and tryptic soy agar amended with 3% NaCl). Consequently, V. parahaemolyticus ATCC 27969, V. parahaemolyticus ATCC 33844, and V. vulnificus ATCC 33815 rapidly reached the viable-but-nonculturable (VBNC) state with increasing levels (≤30%) of NaCl at 4 °C. Within seven days, these pathogens in seafood appeared to enter the VBNC state at 4 °C, as shown by the fluorescence microscopic assay.

Development of a flow chamber system for the reproducible in vitro analysis of biofilm formation on implant materials

Since the introduction of modern dental implants in the 1980s, the number of inserted implants has steadily increased. Implant systems have become more sophisticated and have enormously enhanced patients’ quality of life. Although there has been tremendous development in implant materials and clinical methods, bacterial infections are still one of the major causes of implant failure. These infections involve the formation of sessile microbial communities, called biofilms. Biofilms possess unique physical and biochemical properties and are hard to treat conventionally. There is a great demand for innovative methods to functionalize surfaces antibacterially, which could be used as the basis of new implant technologies. Present, there are few test systems to evaluate bacterial growth on these surfaces under physiological flow conditions. We developed a flow chamber model optimized for the assessment of dental implant materials. As a result it could be shown that biofilms of the five important oral bacteria Streptococcus gordonii, Streptococcus oralis, Streptococcus salivarius, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans, can be reproducibly formed on the surface of titanium, a frequent implant material. This system can be run automatically in combination with an appropriate microscopic device and is a promising approach for testing the antibacterial effect of innovative dental materials.

In situ Biofilm Formation by Multi-species Oral Bacteria Under Flowing and Anaerobic Conditions

An understanding of biofilm behavior of periodontopathic bacteria is key to the development of effective oral therapies. We hypothesized that interspecies bacterial aggregates play an important role in anaerobic biofilm establishment and proliferation, and contribute to the survivability of the biofilm against therapeutic agents. The system developed in this study assessed a multi-species ( Streptococcus gordonii, Actinobacillus actinomycetemcomitans, and Fusobacterium nucleatum) biofilm formation under anaerobic and flowing conditions with the use of an in situ image analysis system. The biofilm was comprised of a base film of non-aggregated cells and complex interspecies aggregates that formed in the planktonic phase which rapidly colonized the surface, reaching 58 ± 9% and 65 ± 11.8% coverage by 5 and 24 hrs, respectively. Upon SDS (0.1%) treatment of a 24-hour biofilm, substantial detachment (55 ± 14%, P < 0.05) of the aggregates was observed, while the base film bacteria remained attached but non-viable. Rapid re-establishment of the biofilm occurred via attachment of viable planktonic aggregates.

Efficacy of various side-to-side toothbrushes and impact of brushing parameters on noncontact biofilm removal in an interdental space model

OBJECTIVES

The objective of this study was to evaluate the efficacy of four different side-to-side toothbrushes and the impact of various brushing parameters on noncontact biofilm removal in an adjustable interdental space model.

MATERIALS AND METHODS

A three-species biofilm, consisting of Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus sanguinis, was formed in vitro on protein-coated titanium disks using a flow chamber combined with a static biofilm growth model. Subsequently, the biofilm-coated disks were exposed to four different powered toothbrushes (A, B, C, D). The parameters distance (0 and 1 mm), brushing time (2, 4, and 6 s), interdental space width (1, 2, and 3 mm), and toothbrush angulation (45° and 90°) were tested. The biofilm volumes were determined using volumetric analyses with confocal laser scanning microscope (Zeiss LSM700) images and Imaris version 7.7.2 software.

RESULTS

The median percentages of simulated interdental biofilm reduction by the tested toothbrushes ranged from 7 to 64 %. The abilities of the analyzed toothbrushes to reduce the in vitro biofilm differed significantly (p < 0.05). Three of the tested toothbrushes (A, B, C) were able to significantly reduce a simulated interdental biofilm by noncontact brushing (p ≤ 0.005). The brushing parameters and their combinations tested in the experiments revealed only minor effects on in vitro interdental biofilm reduction (p > 0.05).

CONCLUSIONS

A three-species in vitro biofilm could be altered by noncontact brushing with toothbrushes A, B, and C in an artificial interdental space model.

CLINICAL RELEVANCE

Certain side-to-side toothbrushes demonstrate in vitro a high efficacy in interdental biofilm removal without bristle-to-biofilm contact.

Quantifying implant-associated biofilms: Comparison of microscopic, microbiologic and biochemical methods

Biofilm-associated infections pose severe problems in modern implant medicine. Screening for new implant materials with antibacterial properties requires reliable quantification of colonizing bacteria. There are many different methods to quantify biofilms on solid surfaces in vitro, employing different (bio-)chemical/microbiological reference parameters. It is therefore difficult to compare studies with different quantification techniques. Here, we have evaluated commonly used microscopic, microbiologic and biochemical methods to quantify bacterial biofilms, in order to clarify their comparability and applicability. Two bacterial species frequently involved in biofilm-associated infections, Staphylococcus aureus and Aggregatibacter actinomycetemcomitans, were used as model organisms; their initial adhesion and biofilm formation on titanium and on antibacterial copper were analyzed using the following methods: LIVE/DEAD fluorescence staining and confocal laser-scanning microscopy, ultrasonic or a newly developed enzymatic detachment followed by standard plate counting (CFU method), a resazurin-based assay, the BacTiter-Glo™ assay and crystal violet staining. The methods differed greatly in complexity, reliability and the applicability to initial adhesion and biofilm formation. To screen biofilm formation on a multitude of surfaces, the resazurin-based and the BacTiterGlo™ assay are well suited. LIVE/DEAD staining and confocal laser-scanning microscopy can be applied for a more detailed analysis of both, initial adhesion and biofilm formation. When using the CFU method for screening purposes, the introduced enzymatic detachment procedure is to be favored over ultrasonic detachment. There is not one single method, which is suitable for all purposes. The appropriate biofilm quantification method has to be chosen on the basis of the specific scientific question.

Deposition and survival of Escherichia coli O157:H7 on clay minerals in a parallel plate flow system

Understanding bacterial pathogens deposition and survival processes in the soil-groundwater system is crucial to protect public health from soilborne and waterborne diseases. However, mechanisms of bacterial pathogen-clay interactions are not well studied, particularly in dynamic systems. Also, little is known about the viability of bacterial pathogens when attached to clays. In this study, a parallel plate flow system was used to determine the deposition kinetics and survival of Escherichia coli O157:H7 on montmorillonite, kaolinite, and goethite over a wide range of ionic strengths (IS) (0.1-100 mM KCl). E. coli O157:H7 deposition on the positively charged goethite is greater than that on the negatively charged kaolinite and montmorillonite. Although the zeta potential of kaolinite was more negative than that of montmorillonite, kaolinite showed a greater deposition for E. coli O157:H7 than montmorillonite, which is attributed to the chemical heterogeneity of clay minerals. Overall, increasing IS resulted in an increase of E. coli O157:H7 deposition on montmorillonite and kaolinite, and a decrease on goethite. Interaction energy calculations suggest that E. coli O157:H7 deposition on clays was largely governed by DLVO (Derjaguin-Landau-Verwey-Overbeek) forces. The loss of bacterial membrane integrity was investigated as a function of time using the Live/Dead BacLight viability assay. During the examined period of 6 h, E. coli O157:H7 retained its viability in suspension and when attached to montmorillonite and kaolinite; however, interaction with the goethite was detrimental. The information obtained in this study is of fundamental significance for the understanding of the fate of bacterial pathogens in soil environments.

Method for the direct observation and quantification of survival of bacteria attached to negatively or positively charged surfaces in an aqueous medium

The risk of groundwater contamination by microbial pathogens is linked to their survival in the subsurface. Although there is a large body of literature on the inactivation behavior of suspended (planktonic) microorganisms, little is known about the inactivation of bacteria when attached to sand grain surfaces in groundwater aquifers. The main goal of this study was to develop a fluorescence-based experimental technique for evaluating the extent of inactivation over time of bacteria adhered onto a surface in an aqueous environment. Key features of the developed technique are as follows: (i) attached cells do not need to be removed from the surface of interest for quantification, (ii) bacterial inactivation can be examined in real-time for prolonged time periods, and (iii) the system remains undisturbed (i.e., the aqueous environment is unchanged) during the assay. A negatively or positively charged substrate (i.e., bare or coated glass slide) was mounted in a parallel-plate flow cell, bacteria were allowed to attach onto the substrate, and the loss of bacterial membrane integrity and respiratory activity were investigated as a function of time by fluorescence microscopy using Live/Dead BacLight and BacLight RedoxSensor CTC (5-cyano-2,3-ditolyl tetrazolium chloride) viability assays. These two different measures of bacterial inactivation result in comparable trends in bacterial inactivation, confirming the validity of the experimental technique. The results of this work show that the developed technique is sensitive enough to distinguish between the inactivation kinetics of different representative bacteria attached to either a negatively charged (bare glass) surface or a positively charged (coated glass) surface. Hence, the technique can be used to characterize bacterial inactivation kinetics when attached to environmentally relevant surfaces over a broad range of groundwater chemistries.

Streptococcus sanguinis adhesion on titanium rough surfaces: effect of shot-blasting particles

Dental implant failure is commonly associated to dental plaque formation. This problem starts with bacterial colonization on implant surface upon implantation. Early colonizers (such as Streptococcus sanguinis) play a key role on that process, because they attach directly to the surface and facilitate adhesion of later colonizers. Surface treatments have been focused to improve osseointegration, where shot-blasting is one of the most used. However the effects on bacterial adhesion on that sort of surfaces have not been elucidated at all. A methodological procedure to test bacterial adherence to titanium shot-blasted surfaces (alumina and silicon carbide) by quantifying bacterial detached cells per area unit, was performed. In parallel, the surface properties of samples (i.e., roughness and surface energy), were analyzed in order to assess the relationship between surface treatment and bacterial adhesion. Rather than roughness, surface energy correlated to physicochemical properties of shot-blasted particles appears as critical factors for S. sanguinis adherence to titanium surfaces.

Visualization of adherent micro-organisms using different techniques

The visualization and quantification of adherent bacteria is still one of the most relevant topics in microbiology. Besides electron microscopic techniques such as transmission electron microscopy, scanning electron microscopy and environmental scanning electron microscopy, modern fluorescence microscopic approaches based on fluorogenic dyes offer detailed insight into bacterial biofilms. The aim of the present review was to provide an overview of the advantages and disadvantages of different methods for visualization of adherent bacteria with a special focus on the experiences gained in dental research.

Adhesion ofStreptococcus sanguinis to glass surfaces measured by isothermal microcalorimetry (IMC)

Bacterial adhesion is the first step in the development of the oral biofilm, called dental plaque. Plaque is the cause of caries, periodontal diseases, and periimplantitis. Investigations of dental plaque, including bacterial adhesion, employ various in vivo and in vitro models using microscopic methods. Microcalorimetry offers another direct approach. The model organism Streptococcus sanguinis is one of the first colonizers adhering to the saliva-coated human tooth surfaces or dental materials within minutes after tooth cleaning. TAM III thermostats, equipped with microcalorimeters, were used for isothermal microcalorimetric (IMC) measurements of heat production as a function of time, expressed by power-time (p-t) curves. Continuous measurements of heat production of growing S. sanguinis cells showed their overall metabolic activity and were highly reproducible. For the adhesion experiments the bacteria were allowed to adhere to different amounts of glass beads. Growing S. sanguinis cells produced a characteristic p-t curve with a maximum of 500 microW at 4.5 h when reaching 10(9) cells ml(-1). The same number of stationary S. sanguinis cells, suspended in PBS produced only approximately 30 microW at 0.5 h due to adhesion. But the amount of heat increased with available glass surface area, indicating that a portion of the heat of adhesion was measured. Similar results were obtained with stationary S. sanguinis cells suspended in human saliva. This study shows that microcalorimetric evaluation of initial bacterial adhesion is indeed possible and may become a rapid, reproducible screening method to study adhesion of different bacteria to different dental materials or to modified surfaces.

Biofilm formation on surface characterized micro-implants for skeletal anchorage in orthodontics

Micro-implants are increasingly popular in clinical orthodontics to effect skeletal anchorage. However, biofilm formation on their surfaces and subsequent infection of peri-implant tissues can result in either exfoliation or surgical removal of these devices. The present study aimed to assess biofilm formation on five commercially available, surface characterized micro-implant systems in vitro. The elemental surface compositions of as-received and autoclave-sterilized micro-implants were characterized by X-ray photoelectron spectroscopy. High carbon contamination was detected on the oxide surfaces, along with traces of inorganic elements (Ca, Cu, Cr, Pb, Zn, and P) which disappeared after Ar(+) ion sputtering. The mean surface roughnesses (R(a)) were around 182nm for titanium micro-implants, and 69nm for stainless steel micro-implants, as measured by atomic force microscopy. Scanning electron microscopy revealed different surface topographies between manufacturers, varying from typical machined grooves to structural defects like pores and pits. Overnight biofilms were grown on micro-implant surfaces by immersion in pooled human whole saliva. Biofilms on micro-implants treated with chlorhexidine and fluoride mouthrinses contained comparable numbers of viable organisms, but significantly less than did untreated micro-implants. Comparison of different implant systems using multiple linear regression analysis indicated that biofilm formation was governed by roughness of the implant surface and the prevalence of carbon- and oxygen-rich components.

In vitro biofilm formation on the surface of resin-based dentine adhesives

Prevention of root caries on exposed root surfaces in the aging population is a significant challenge. Bonding resins can be applied to exposed root surfaces as sealants; however, minimal data exists regarding biofilm formation on the surface of these resins. We hypothesized that an antibacterial dentine-bonding resin containing methacryloxydodecyl-pyridiniumbromide (MDPB) may reduce biofilm formation. Biofilms were produced in pooled stimulated natural whole saliva, supplemented with 1% sucrose, on the surface of 5 dentine-bonding resins (Clearfil SE, OptiBond Solo, Protect Bond, Protect Bond Primer, and Xeno III) using untreated root surfaces as controls. Biofilms were stained using the Live:Dead Baclight bacterial viability stain, viewed with confocal microscopy, and analyzed using ImageJ image-analysis software. Resin surfaces encouraged attachment of live bacteria compared with root surfaces. All resins showed similar bacterial colonization in sections adjacent to the resin surface, but in the central and outer portions of biofilms, Xeno III and Protect Bond Primer showed a viable bacterial load similar to that of the root surface. Fluoride-releasing resins (OptiBond Solo/Protect Bond) did not show reduced biofilm formation. Thus, antibacterial agents within the resins have a minimal effect on biofilm formation, particularly when directly adjacent to the root surface.

Streptococcal diversity in oral biofilms with respect to salivary function

OBJECTIVE

In a previous study, we screened 149 subjects and established four groups high or low for salivary killing of oral bacteria, and for aggregation and live and dead adherence of oral bacteria (as a combined factor). Caries scores were significantly lower in both High Aggregation-Adherence groups. In this study we looked at the effects of those differences in salivary function on the quantity and diversity of oral biofilm streptococci.

DESIGN

Subjects from those four groups were recalled for collection of overnight oral biofilm from buccal upper central incisors, lingual lower central incisors, buccal upper and lower first molars, and lingual upper and lower first molars. At each site, groups were compared for total biofilm (by DNA concentration), total streptococci (by quantitative PCR), and streptococcal diversity (by Streptococcus-specific denaturing gradient gel electrophoresis).

RESULTS

Total biofilm DNA and total streptococci were correlated. Both were highest on buccal molar surfaces and lowest on lingual lower central incisors, and both were significantly lower in the High Aggregation-Adherence groups (particularly at the buccal molar site). Fifty distinct bands were observed in denaturing gradient gels. There was great diversity within and between sites. Three major bands were present in almost every person at every site. Densities for two of those bands were significantly lower in both High Aggregation-Adherence groups. Other less-prevalent bands also showed the same pattern.

CONCLUSION

These findings are consistent with our caries results in suggesting that differences in salivary function can influence the quantity and composition of streptococci in oral biofilms.

Comparison of antiadhesive and antibacterial effects of antiseptics on Streptococcus sanguinis

Three antiseptic (chlorhexidine, Olaflur, Octenisept) and one putative antiadhesive (chitosan) agent were investigated for their effect on viable planktonic and attached Streptococcus sanguinis cells. The bacterial pretreatment with each chemotherapeutic was performed in two steps: (i) After the exposure of planktonic streptococci to the antiseptics, the cells were suspended in human sterile saliva and allowed to attach to human enamel for 60 min; (ii) After 60 min in the flow chamber system, initially attached streptococci were treated with these agents. The microbial viability was monitored by the percentage of vital streptococci determined by fluorescence microscopy and cell reproduction. In comparison with the negative control NaCl, the non-bactericidal chitosan derivative showed distinctive antiadhesive properties. For both treatment procedures, the efficacy of the antiseptics in reducing the viability of planktonic and attached streptococci was Octenisept > Olaflur > chlorhexidine > saline > chitosan. Further studies appear warranted to develop new antiplaque/antibiofilm strategies involving highly efficient bactericidals with antiadhesive formulations.

Simultaneous measurement of the viability, aggregation, and live and dead adherence of Streptococcus crista, Streptococcus mutans and Actinobacillus actinomycetemcomitans in human saliva in relation to indices of caries, dental plaque and periodontal disease

Salivary proteins have multiple functions and many share similar functions, which may be why it has been difficult to relate variations in their concentrations to oral health and ecology. An alternative is to focus on variations in the major functions of saliva. An hydroxyapatite-coated microplate model has been developed that simultaneously measures saliva-promoted bacterial viability, bacterial aggregation, and live and dead bacterial adherence, while simulating oral temperature and shearing forces from swallowing. That model was applied to resting whole and stimulated parotid saliva from 149 individuals, using representative strains of Streptococcus crista, S. mutans, and Actinobacillus actinomycetemcomitans. Two major factors were defined by multivariate analysis (this was successful only for whole-saliva). One factor was correlated with aggregation, live adherence and dead adherence for all three strains; the other was correlated with total viability of all three strains. Participants were grouped <25th percentile and >75th percentile for each factor. Those groups were compared for clinical indices of oral health. Caries scores were significantly lower in those with high scores for aggregation-adherence, regardless of whether total viability scores were low or high. Live bacteria always predominated on surfaces when live and dead adherence scores were expressed as ratios. However, participants with high scores for aggregation-adherence showed significantly more dead adherent bacteria than those with low scores (these ratios were uncorrelated with total viability). This finding may indicate that extreme differences in the ability to kill bacteria on surfaces can influence caries risk.

Vitality status of microorganisms in infected human root dentine

AIM

This experimental study was initiated to establish a method for characterizing the vitality status of bacteria in infected human root dentine by differentiating between viable and dead microorganisms.

METHODOLOGY

Twenty-four root segments of extracted human teeth were infected with either Streptococcus sanguinis or Enterococcus faecalis for 8 weeks. Baseline samples from root dentine (rd) were collected after 4 weeks. These were compared with samples taken at week 8 (control group: n = 12) and with samples collected at week 12 after calcium hydroxide treatment for four weeks (test group: n = 12). After marking viable and dead bacterial cells by two fluorescent dyes, the portion of viable bacteria (PVB) was determined, as well as the number of colony-forming units (CFU).

RESULTS

Viable and dead bacteria were identified in all "rd" samples. PVBrd values were lower than PVB values of the bacterial suspension in the root canal lumen. In the control group, PVBrd and CFUrd did not markedly differ at week 4 and at week 8, regardless of the strain used. In the test group, viable but non-culturable sanguinis streptococci (mean PVBrd = 27%; CFUrd = 0) were detected, despite calcium hydroxide treatment. The viability of E. faecalis was not affected by calcium hydroxide.

CONCLUSIONS

Fluorescence labelling of bacteria in human root dentine gives valuable additional information about their vitality status compared to the parameter CFU. The method may be suitable for following the fate of bacteria in dentinal tubules, for example in the presence of intracanal dressings.

Bactericidal effect of delmopinol on attached and planktonic Streptococcus sanguinis cells

The aim of this investigation was to determine the antibacterial effect of varying concentrations of delmopinol-HCl on attached as well as on planktonic Streptooccus sanguinis cells in vitro. In addition, a possible antiadhesive effect on attached micro-organisms was to be investigated. S. sanguinis cells were allowed to attach to glass surfaces. These as well as planktonic cells were exposed to delmopinol-HCI in concentrations ranging from 0.2% to 0.00005% for 2 min. The percentage of vital bacteria was calculated by means of a fluorescence staining method. Total counts of attached bacteria were performed to determine any possible detaching effect by the delmopinol-HCl. The CFU were determined for the planktonic bacteria. Attached as well as planktonic bacteria showed a marked decrease in vitality following exposure to 0.2% delmopinol-HCl. After exposure to 0.05% this was only the case with the attached microorganisms. The total number of attached bacteria was not reduced by the delmopinol treatment. During initial dental biofilm formation, delmopinol-HCl causes a bactericidal effect when applied in concentrations of 0.05% and higher.

The ability of direct fluorescence-based, two-colour assays to detect different physiological states of oral streptococci

AIMS

To investigate the ability of six fluorescent-based, two-colour viability assays to detect different physiological growth stages of two oral streptococci species.

METHODS AND RESULTS

The growth of Streptococcus sanguinis and Strep. mutans from 0 to 73 h culture periods was monitored by cell labelling with six mixtures of fluorescent stains, in addition to the growth parameters optical density (O.D.), log values of the total cell counts (log BC ml(-1)) and of the colony-forming units (log cfu ml(-1)).

CONCLUSION

In comparison with the corresponding cfu values as control, the vitality proportions determined by the Syto 9/PI test best reflected the dynamic growth pattern of both test strains. The direct fluorescent-based, two-colour assay Syto 9/PI provides valuable information about microbial viability stages.

SIGNIFICANCE AND IMPACT OF THE STUDY

The detection of viable but non-culturable bacteria requires more precise direct methods such as the fluorescent staining technique presented here, in addition to the classical plate count method.

Conofocal microscopy study of undisturbed and chlorhexidine-treated dental biofilm

Culturing of dispersed plaque samples and vitality staining of plaque smears are the most commonly used methods for evaluating the effects of antimicrobials on dental plaque. The visualization of the antimicrobial action on oral biofilm present on the substrate surface (in situ) would add valuable information to the existing knowledge about the treatment effects. This study aimed at combining the advantage of confocal laser scanning microscopy (CLSM) to visualize plaque non-destructively with a vitality staining technique to assess the immediate bactericidal effect of chlorhexidine (CHX) on biofilm. Three 200-microm-wide grooves were cut into bovine dentin discs for plaque accumulation. The discs were worn by six subjects for 6, 24, and 48 hrs, then broken into halves, one of which received a one-minute extraoral 0.2% CHX treatment, while the other served as control. Both halves were stained for vital fluorescence measurements and visualized by CLSM. Plaque vitality (in %) was quantified by image analysis in three plaque layers-outer, middle, and inner. The CHX effect was significant in six-hour samples (p < 0.001) and only in the outer layer of the 48-hour plaque (p < 0.001), demonstrating a resistant nature of dental biofilm to a single CHX treatment. With the present approach, we have shown that it is possible to visualize and quantitate the antimicrobial treatment effect on biofilm still present on the substrate on which it was grown.

Spatial distribution of vital and dead microorganisms in dental biofilms

To examine the spatial structure of dental biofilms a vital fluorescence technique was combined with optical analysis of sections in a confocal laser scanning microscope (CLSM). Enamel slaps were worn in intraoral splints by three volunteers for five days to accumulate smooth-surface plaque. After vital staining with fluorescein diacetate and ethidium bromide the specimens were processed for CLSM examination. Optical sections 1 microm apart were analysed in the z-axis of these dental biofilms. One of the films was 15 microm high, sparse and showed low vitality, i.e. <16%, while the others were taller (25 and 31 microm) and more vital, i.e. up to 30 and 69%, respectively. In all instances the bacterial vitality increased from the enamel surface to the central part of the plaque and decreased again in the outer parts of the biofilm. The spatial arrangement of the microorganisms in the biofilm showed voids outlined by layers of vital bacteria, which themselves were packed in layers of dead material.

Saliva and dental plaque

Dental plaque is being redefined as oral biofilm. Diverse overlapping microbial consortia are present on all oral tissues. Biofilms are structured, displaying features like channels and projections. Constituent species switch back and forth between sessile and planktonic phases. Saliva is the medium for planktonic suspension. Several major functions can be defined for saliva in relation to oral biofilm. It serves as a medium for transporting planktonic bacteria within and between mouths. Bacteria in transit may be vulnerable to negative selection. Salivary agglutinins may prevent reattachment to surfaces. Killing by antimicrobial proteins may lead to attachment of dead cells. Salivary proteins form conditioning films on all oral surfaces. This contributes to positive selection for microbial adherence. Saliva carries chemical messengers which allow live adherent cells to sense a critical density of conspecifics. Growth begins, and thick biofilms may become resistant to antimicrobial substances. Salivary macromolecules may be catabolized, but salivary flow also may clear dietary substrates. Salivary proteins act in ways that benefit both host and microbe. All have multiple functions, and many do the same job. They form heterotypic complexes, which may exist in large micelle-like structures. These issues make it useful to compare subjects whose saliva functions differently. We have developed a simultaneous assay for aggregation, killing, live adherence, and dead adherence of oral species. Screening of 149 subjects has defined high killing/low adherence, low killing/high adherence, high killing/high adherence, and low killing/low adherence groups. These will be evaluated for differences in their flora.