The validity of models

Anti-cariogenic effect of experimental resin cement containing ursolic acid using dental microcosm biofilm

OBJECTIVE

This study aimed to assess the anticariogenic effects of resin cement containing varying ursolic acid (UA) concentrations and to determine the optimal UA concentrations in the microcosm biofilm model.

MATERIALS AND METHODS

Experimental resin cements with UA concentrations of 0, 0.1, 0.5, 1.0, and 2.0 wt% were prepared. Class I cavities were prepared on 50 extracted human molars and restored with composite inlays and experimental resin cements. Tooth samples were subjected to artificial caries induction for 10 days in a microcosm biofilm model using human saliva as an inoculum, and then mineral changes were evaluated using quantitative light-induced fluorescence (ΔF and ΔQ) and micro-computed tomography (CT). The bacterial composition of the human saliva was analyzed by 16s RNA microbiome profiling. One-way analysis of variance with Tukey and Duncan post-hoc tests was employed for statistical analysis (p < 0.05).

RESULTS

As the UA concentration increased, resin cement decreased ΔF and ΔQ before and after caries induction but showed a significant difference only in ΔQ at UA concentration ≥ 1.0% (p < 0.05). The gray value analysis result of micro CT also showed a significant difference at UA concentration ≥ 1.0% (p < 0.05). In the human saliva analysis, bacterial composition remained within normal oral microbiota ranges.

CONCLUSION

Resin cements containing at least 1.0% of UA exhibited an anticariogenic effect on dental microcosm biofilms.

CLINICAL RELEVANCE

To reduce the failure of restorations, it is essential to prevent the occurrence of secondary caries. The application of UA in resin cement can be utilized to prevent the formation of secondary caries due to the anticariogenic effect of UA.

Biofilm reactor calibration for in vitro investigation of composite biodegradation

Introduction: The majority of biodegradation studies of composite materials use simplified models of microbial biofilm despite the apparent diversity of the oral microbiota. The use of in vitro systems of “artificial mouth” design is a step towards clarifying the synergistic effect that microbial plaque and human saliva have on composite degradation.

Aim: Establishment of functional parameters for in vitro reproduction of oral biofilms via biofilm reactor systems.

Materials and methods: The CDC Biofilm Reactor system consists of eight polypropylene sticks. The rod cover and the retaining plates are mounted in a 1-dm glass cylinder with an outlet side opening. The laboratory bioreactor has a working volume of 340 ml. The device is equipped with a four-blade magnetic stirrer. The system also includes gauging appliances and executive mechanisms for controlling and adjusting the basic parameters of the process.

Results: Determination of the operating volume of the reactor is performed prior to the experiment along with the time of reach and stabilization of the set temperature in the design which is 60 min at 120 rpm. A mathematical model is used to calculate the rate of delivery of growth medium - 11 millilitres per minute. The bioreactor is sterilized by 0.3% neomycin solution for 24 hours. Prior to the experiment the system is cleansed (via passage) with sterile water for 60 minutes.

Conclusions: The pre-calibration of a bioreactor system allows specification and refinement of its working parameters, thus engaging for accurate reproduction of the environmental conditions in the oral cavity.

The Open Challenge of in vitro Modeling Complex and Multi-Microbial Communities in Three-Dimensional Niches

The comprehension of the underlying mechanisms of the interactions within microbial communities represents a major challenge to be faced to control their outcome. Joint efforts of in vitro, in vivo and ecological models are crucial to controlling human health, including chronic infections. In a broader perspective, considering that polymicrobial communities are ubiquitous in nature, the understanding of these mechanisms is the groundwork to control and modulate bacterial response to any environmental condition. The reduction of the complex nature of communities of microorganisms to a single bacterial strain could not suffice to recapitulate the in vivo situation observed in mammals. Furthermore, some bacteria can adapt to various physiological or arduous environments embedding themselves in three-dimensional matrices, secluding from the external environment. Considering the increasing awareness that dynamic complex and dynamic population of microorganisms (microbiota), inhabiting different apparatuses, regulate different health states and protect against pathogen infections in a fragile and dynamic equilibrium, we underline the need to produce models to mimic the three-dimensional niches in which bacteria, and microorganisms in general, self-organize within a microbial consortium, strive and compete. This review mainly focuses, as a case study, to lung pathology-related dysbiosis and life-threatening diseases such as cystic fibrosis and bronchiectasis, where the co-presence of different bacteria and the altered 3D-environment, can be considered as worst-cases for chronic polymicrobial infections. We illustrate the state-of-art strategies used to study biofilms and bacterial niches in chronic infections, and multispecies ecological competition. Although far from the rendering of the 3D-environments and the polymicrobial nature of the infections, they represent the starting point to face their complexity. The increase of knowledge respect to the above aspects could positively affect the actual healthcare scenario. Indeed, infections are becoming a serious threat, due to the increasing bacterial resistance and the slow release of novel antibiotics on the market.

Mini-review: from in vitro to ex vivo studies: an overview of alternative methods for the study of medical biofilms

Microbial biofilms are a natural adaptation of microorganisms, typically composed of multiple microbial species, exhibiting complex community organization and cooperation. Biofilm dynamics and their complex architecture are challenging for basic analyses, including the number of viable cells, biomass accumulation, biofilm morphology, among others. The methods used to study biofilms range from in vitro techniques to complex in vivo models. However, animal welfare has become a major concern, not only in society, but also in the academic and scientific field. Thus, the pursuit for alternatives to in vivo biofilm analyses presenting characteristics that mimic in vivo conditions has become essential. In this context, the present review proposes to provide an overview of strategies to study biofilms of medical interest, with emphasis on alternatives that approximate experimental conditions to host-associated environments, such as the use of medical devices as substrata for biofilm formation, microcosm and ex vivo models.

The antimicrobial and cytotoxic effects of a copper-loaded zinc oxide phosphate cement

Objectives

Evidence about modifications of dental luting materials to minimize biological failure at the “marginal gap” between teeth and fixed prosthodontics is scarce. We compared a copper-modified (Co-ZOP) and a conventional zinc oxide phosphate cement (ZOP) in terms of antimicrobial and cytotoxic potentials in vitro and in vivo.

Materials and methods

Specimens of ZOP and Co-ZOP were characterized by the mean arithmetic roughness (Ra) and surface free energy (SFE). Powder components were examined using scanning electron microscopy (SEM). Energy-dispersive X-ray spectroscopy (EDX) showed elemental material compositions. In vitro microbial adhesion was shown using SEM, luminescence, and fluorescence assays. CCK-8 assays of mouse fibroblasts (L929) and human gingival fibroblasts (GF-1) were performed after 6, 24, and 48 h of specimen incubation. In vivo, ZOP and Co-ZOP specimens were applied intraorally for 12 h; biofilm accumulation was shown using SEM.

Results

Ra of ZOP and Co-ZOP showed no significant differences; SFE was significantly higher for Co-ZOP. EDX exhibited minor copper radiation for Co-ZOP, none for ZOP. In vitro fungal adhesion to Co-ZOP was significantly higher than to ZOP; in vitro streptococcal adhesion, cytotoxicity, and in vivo biofilm formation were not significantly different.

Conclusions

Co-ZOP showed low surface allocations of copper with no improved antimicrobial properties compared with conventional ZOP in vitro or in vivo.

Clinical relevance

Antimicrobial effects and low cytotoxicity of biomaterials are important for the clinical outcome. Based on our in vitro and in vivo results, no clinical recommendation can be given for the tested Co-ZOP.

Dental Biofilm and Laboratory Microbial Culture Models for Cariology Research

Dental caries form through a complex interaction over time among dental plaque, fermentable carbohydrate, and host factors (including teeth and saliva). As a key factor, dental plaque or biofilm substantially influence the characteristic of the carious lesions. Laboratory microbial culture models are often used because they provide a controllable and constant environment for cariology research. Moreover, they do not have ethical problems associated with clinical studies. The design of the microbial culture model varies from simple to sophisticated according to the purpose of the investigation. Each model is a compromise between the reality of the oral cavity and the simplification of the model. Researchers, however, can still obtain meaningful and useful results from the models they select. Laboratory microbial culture models can be categorized into a closed system and an open system. Models in the closed system have a finite supply of nutrients, and are also simple and cost-effective. Models in the open system enabled the supply of a fresh culture medium and the removal of metabolites and spent culture liquid simultaneously. They provide better regulation of the biofilm growth rate than the models in the closed system. This review paper gives an overview of the dental plaque biofilm and laboratory microbial culture models used for cariology research.

The Oral Microbiota

The oral microbiota represents an important part of the human microbiota, and includes several hundred to several thousand diverse species. It is a normal part of the oral cavity and has an important function to protect against colonization of extrinsic bacteria which could affect systemic health. On the other hand, the most common oral diseases caries, gingivitis and periodontitis are based on microorganisms. While (medical) research focused on the planktonic phase of bacteria over the last 100 years, it is nowadays generally known, that oral microorganisms are organised as biofilms. On any non-shedding surfaces of the oral cavity dental plaque starts to form, which meets all criteria for a microbial biofilm and is subject to the so-called succession. When the sensitive ecosystem turns out of balance - either by overload or weak immune system - it becomes a challenge for local or systemic health. Therefore, the most common strategy and the golden standard for the prevention of caries, gingivitis and periodontitis is the mechanical removal of this biofilms from teeth, restorations or dental prosthesis by regular toothbrushing.

Use of a high-throughput in vitro microfluidic system to develop oral multi-species biofilms

There are few high-throughput in vitro systems which facilitate the development of multi-species biofilms that contain numerous species commonly detected within in vivo oral biofilms. Furthermore, a system that uses natural human saliva as the nutrient source, instead of artificial media, is particularly desirable in order to support the expression of cellular and biofilm-specific properties that mimic the in vivo communities. We describe a method for the development of multi-species oral biofilms that are comparable, with respect to species composition, to supragingival dental plaque, under conditions similar to the human oral cavity. Specifically, this methods article will describe how a commercially available microfluidic system can be adapted to facilitate the development of multi-species oral biofilms derived from and grown within pooled saliva. Furthermore, a description of how the system can be used in conjunction with a confocal laser scanning microscope to generate 3-D biofilm reconstructions for architectural and viability analyses will be presented. Given the broad diversity of microorganisms that grow within biofilms in the microfluidic system (including Streptococcus, Neisseria, Veillonella, Gemella, and Porphyromonas), a protocol will also be presented describing how to harvest the biofilm cells for further subculture or DNA extraction and analysis. The limits of both the microfluidic biofilm system and the current state-of-the-art data analyses will be addressed. Ultimately, it is envisioned that this article will provide a baseline technique that will improve the study of oral biofilms and aid in the development of additional technologies that can be integrated with the microfluidic platform.

Correlation between the cariogenic response in biofilms generated from saliva of mother/child pairs

This study aimed to correlate the cariogenic responsiveness of biofilms generated from the saliva of mothers and children. The mother-child pairs were classified according to the children's caries levels: caries-free, early childhood caries (ECC) or severe ECC. Microcosm biofilms were grown on enamel discs for 10 days. Factors under evaluation were caries experience levels, inoculum source (mothers and children) and growth conditions including cariogenic challenge (growth medium provided with and without sucrose) and no cariogenic challenge (growth medium sucrose-free). Statistical analysis was performed with ANOVA and Tukey's test, and the Spearman correlation test. Regular sucrose exposure resulted in a higher surface hardness change (%SHC). The correlation between biofilms formed from saliva of mother-child pairs was significant regarding pH, total aciduric microorganisms and lactobacilli counts under cariogenic challenge. Biofilm growth originating from mother-child pairs under regular sucrose exposure promoted the same cariogenic response independently of caries experience and the microbiological profile of the donors.

In vitro efficacy of cold atmospheric pressure plasma on S. sanguinis biofilms in comparison of two test models

Dental plaque critically affects the etiology of caries, periodontitis and periimplantitis. The mechanical removal of plaque can only be performed partially due to limited accessibility. Therefore, plaque still represents one of the major therapeutic challenges. Even though antiseptic mouth rinses reduce the extent of biofilm temporarily, plaque removal remains incomplete and continuous usage can even result in side effects. Here we tested argon plasma produced by kinpen09 as one option to inactivate microorganisms and to eliminate plaque. S. sanguinis biofilms cultivated in either the European Biofilm Reactor (EUREBI) or in 24 well plates were treated with argon plasma. In both test systems a homogeneous, good analyzable and stable biofilm was produced on the surface of titan plates within 72 h (>6,9 log10 CFU/ml). Despite the significantly more powerful biofilm production in EUREBI, the difference of 0.4 log10 CFU/ml between EUREBI and the 24 well plates was practically not relevant. For that reason both test models were equally qualified for the analysis of efficacy of cold atmospheric pressure plasma. We demonstrate a significant reduction of the biofilm compared to the control in both test models. After plasma application of 180 s the biofilm produced in EUREBI or in 24 well plates was decreased by 0.6 log10 CFU/ml or 0.5 log10 CFU/ml, respectively. In comparison to recently published studies analyzing the efficacy of kinpen09, S. sanguinis produces a hardly removable biofilm. Future investigations using reduced distances between plasma source and biofilm, various compositions of plasma and alternative plasma sources will contribute to further optimization of the efficacy against S. sanguinis biofilms.

Self-etching dental adhesive containing a natural essential oil: anti-biofouling performance and mechanical properties

This study assessed the anti-biofouling performance of an experimental adhesive system containing a naturally occurring essential vegetable oil and examined the following physical and mechanical properties: water sorption (WS) and solubility (SL), microtensile bond strength to dentin (μTBS), and degree of conversion. The following six groups were tested: a self-etching experimental adhesive containing refined essential oil from the seeds of the Butia capitata tree (EAO); an oil-free version of the experimental adhesive (EANO); one group without adhesive as the control (C); and the three following commercial self-etching adhesives: Clearfil Protect Bond (CPB), Clearfil SE Bond, and Adper SE Plus. The antibacterial effect was estimated by microbiological culture on selective/non-selective media, and the results expressed as colony-forming units per unit weight of dry biofilm (CFU mg(-1)). The data were submitted to ANOVA and Tukey's post hoc test (α = 0.05). After 24 h, pH changes were similar in the storage medium of all tested adhesive systems. EAO showed similar levels of antimicrobial activity in a model biofilm microcosm as the commercial self-etching adhesive CPB. Both were effective against total microorganisms, aciduric bacteria, lactobacilli, and Streptococcus mutans. WS and SL were not affected by the presence of the essential oil; the values of EAO were similar to or less than those of commercial equivalents. The incorporation of an essential oil into an experimental adhesive did not influence its monomer conversion result. Immediate μTBS values of EAO and EANO were similar and were greater than those of commercial equivalents. After storage for 6 months, the μTBS of the EAO decreased significantly and became similar to the values of commercial equivalents, while the strength of the EANO was not affected.

Effect of food preservatives on in situ biofilm formation

The aim of this double-blind, controlled crossover study was to evaluate the influence of food preservatives on in situ dental biofilm growth. Twenty-four volunteers wore appliances with six specimens each of bovine enamel to build up intra-oral biofilms. During three test cycles, the subjects had to put one half of the appliance twice a day in one of the assigned active solutions (0.1% benzoate, BA; 0.1% sorbate, SA or 0.2% chlorhexidine, CHX) and the other into NaCl. After 5 days, the developed biofilms were stained with two fluorescent dyes to visualise vital (green) and dead bacteria (red). Biofilms were scanned by confocal laser scanning microscopy and biofilm thickness (BT) and bacterial vitality (BV%) were calculated. After a washout period of 7 days, a new test cycle was started. The use of SA, BA and CHX resulted in a significantly reduced BT and BV compared to NaCl (p<0.001). Differences between SA and BA were not significant (p>0.05) for both parameters, while CHX showed significantly lower values. Both preservatives showed antibacterial and plaque-inhibiting properties, but not to the extent of CHX. The biofilm model enabled the examination of undisturbed oral biofilm formation influenced by antibacterial components under clinical conditions.

Caries-related plaque microcosm biofilms developed in microplates

In vivo dental plaque biofilms consist of complex communities of oral bacteria that are a challenge to replicate in vitro. The aim of this investigation was to establish human dental plaque microcosms in microplates to reflect conditions that are relevant to dental caries. Microcosm plaque biofilms were initiated from the saliva of two different donors, grown for up to 10 days in 24-welled microplates on Thermanox coverslips in various types of artificial saliva with and without sucrose, which were replaced daily. Microbiota composition of 40 species associated with oral health and dental caries was monitored in the plaques using Checkerboard DNA-DNA hybridization analysis. pH was measured as an indicator of cariogenic potential. The composition of the saliva inocula was different, and yielded plaque microcosms with different composition and growth responses to sucrose. Artificial saliva type and presence of sucrose, and the resulting growth and pH conditions, modified the growth of individual species and hence the ecological profile of the microplate plaques during development. Complex population shifts were observed during development, and older plaques comprised predominantly facultative anaerobic species. Sucrose supplementation limited the decline of Streptococci over time but did not increase the abundance of mutans Streptococci. Sucrose at 0.15% increased levels of caries-associated species including Lactobacillus fermentum, Lactobacillus acidophilus and Actinomyces gerensceriae; these were further increased with sucrose at 0.5%, in addition to Actinomyces israelii, Rothia dentocariosa and Capnocytophaga gingivalis. The microplate plaques demonstrated complex community dynamics that appeared to reflect the maturation of natural plaques, and sucrose induced a cariogenic plaque composition and pH.

A laboratory model biofilm fermenter: design and initial trial on a single species biofilm

BACKGROUND

The minimum inhibitory concentration (MIC) does not provide information on the efficacy of antimicrobial agents against infections involving biofilms, which are many times more resistant than planktonic forms of bacteria. This report is on the design and initial trial of a device for growing standard biofilms and testing antimicrobial agents.

METHODS

We constructed a durable, autoclaveable laboratory model biofilm fermenter (LMBF) that holds hydroxyapatite discs 300 microm below a surface onto which an artificial saliva medium drips at a rate comparable to human salivary flow. Inoculated with Streptococcus sanguinis, the device formed biofilms that were swept with a Teflon wiper under aerobic conditions. Five-day-old biofilm-coated discs were aseptically removed and placed in 3 ml of sterile saline, 0.12% chlorhexidine gluconate, or 0.1% phosphate-buffered chlorine dioxide mouthwash for 1 minute. The discs and test agent were immediately diluted with saline to 10 ml, vortexed for 30 seconds, serially diluted, plated on blood agar, and incubated anaerobically 2 days. Bacterial counts were done, and the MIC of each mouthwash was determined.

RESULTS

In tests with sterile water and sterile medium, the device maintained a closed system. After inoculation with S. sanguinis, a steady state was reached at day 5. Chlorhexidine at stock concentration achieved about a 2 log10 reduction (P = 0.002), but never achieved complete killing. Chlorine dioxide had no significant effect. The MIC against planktonic S. sanguinis was 112.8 microg/ml for chlorhexidine and 9.0 microg/ml for chlorine dioxide.

CONCLUSIONS

The LMBF generates and maintains a single-species oral model biofilm to a steady state and enables in vitro tests of disinfectant mouthwashes in simulated clinical use. It should be usable for more advanced tests of multiple species biofilms.

Bacterial Biofilm Development on Hydroxyapatite-Coated Glass

Glass plates are frequently used as the substratum in flow cell experiments to allow continuous non-destructive observations of biofilm development via microscopy. The aim of this study was to evaluate hydroxyapatite-coated glass as a substratum for flow cell experiments, in comparison to plain glass, for modelling primary colonization of the tooth surface by Streptococcus sanguis. Glass plates were magnetron sputter coated with hydroxyapatite, producing a thin transparent layer. Biofilm development in the flow cell was recorded using image capture from a microscope, and images were analyzed to determine percentage coverage of the substratum over 24 h. Removal of biofilm by increasing the flow rate was also assessed. No statistically significant differences were detected between S. sanguis biofilms grown on the two different substratum materials. Hence, this work supports the proposal that the conditioning film reduces the influence of substratum surface properties.

Role of urease enzymes in stability of a 10-species oral biofilm consortium cultivated in a constant-depth film fermenter

Using a 10-species oral biofilm consortium and defined mutants, we show that high-level capacity to generate ammonia from a common salivary substrate is needed to maintain community diversity. This model appears to be suitable for the study of the effects of individual genetic determinants on the ecology of oral biofilms.

In vitro assessment of the plaque-removing ability of hydrodynamic shear forces produced beyond the bristles by 2 electric toothbrushes

BACKGROUND

The aim of this study was to compare the efficacy of interproximal plaque removal by the hydrodynamic shear forces produced by 2 electric toothbrushes (toothbrush A, Sonicare Plus and toothbrush B, Braun Oral B) using laboratory-grown plaque biofilms in an anatomically correct in vitro brushing model.

METHODS

In vitro oral biofilms were grown in a constant-depth film fermenter on hydroxyapatite (HA) discs. Brushing experiments were conducted in a specially constructed machine designed to simulate the brushing of interproximal plaque between mandibular molar teeth; the bristles of the toothbrush did not make contact with the biofilm at any time. The load force between the brushes and teeth were in accordance with typical use and an exposure time of 5 seconds was used throughout. The efficacy of brushing was assessed by enumeration of the percentage of viable bacteria removed from the HA discs. These experiments were conducted with the electronic effect of the toothbrushes either activated or inactivated.

RESULTS

Activation of toothbrush A significantly (P = 0.004) increased the median percentage of bacteria removed from 0.47% to 48.45%. Likewise, activation of toothbrush B significantly (P = 0.015) increased the median percentage of bacteria removed from 2.85% to 15.86%. The median percentage of plaque bacteria removed by the active toothbrush A was significantly (P = 0.009) greater than that removed by toothbrush B in this model system.

CONCLUSION

These data imply that toothbrush A would be more effective than toothbrush B at removing interproximal dental plaque in vivo.

Evaluating biofilm growth of two oral pathogens

AIMS

To determine the expediency of a microtitre assay system for establishing, quantifying and antimicrobial testing of two representative oral pathogens.

METHODS AND RESULTS

Streptococcus mutans and Porphyromonas gingivalis were used. Morphological characteristics of the attached population were evaluated. Biofilm growth was evaluated spectrophotometrically (undisturbed and 1 N NaOH dissipated biofilm). The minimum concentration of chlorhexidine gluconate that inhibited biofilm growth was determined. Growth of the biofilms was successfully monitored by direct optical density measurements or those re-suspended in 1 N NaOH. The latter was necessary when glucans were present in Strep. mutans biofilms. The minimum concentration of chlorhexidine gluconate that inhibited biofilm growth was 1.25 microg ml(-1) for both species. The attached bacteria exhibited common biofilm characteristics.

SIGNIFICANCE AND IMPACT OF THE STUDY

The assay system developed was especially useful for monitoring the growth of adherent Strep. mutans in the presence of glucans, which is particularly significant for the study of anti-plaque chemicals.

An in vitro model for studying the contributions of the Streptococcus mutans glucan-binding protein A to biofilm structure

The method described here for analyzing biofilms was sensitive enough to allow the detection of differences formed by pure cultures of S. mutans or a GbpA knockout strain. Other strains have also been tested, and the differences in biofilm structure were sometimes even more extensive (data not shown). The advantages of this method are that it is quick, inexpensive, and adaptable to almost any laboratory setting. The constant rotation of the cultures, which was employed to simulate salivary flow, appears to be a critical element for establishing biofilm differences. An analysis of protein profiles confirmed that the biofilm bacteria were metabolically distinct from the planktonic phase bacteria. For the strains tested, the variations in biofilm architecture could be visualized with or without magnification. Staining of the bacteria was not required, though we typically stained the biofilms with either crystal violet or Schiff's reagent. Altogether, this in vitro method for generating biofilms allowed the evaluation of visual, quantitative (confocal microscopy), and functional (antimicrobial susceptibility) differences. We have employed these methods in a reductionist approach to understanding the contribution of individual proteins to dental plaque development. These methods may also be useful in the screening of mutants that would be of greatest for testing in multispecies biofilms, animal models, or more complex biofilm models.

Physiologic homeostasis and stress responses in oral biofilms

Studies performed since the early, 1970s have yielded tremendous amounts of information about the physiology, genetics, and interactions of oral bacteria. This pioneering work has provided a solid foundation to begin to apply the knowledge and technologies developed using suspended populations for studying oral bacteria under conditions that more closely mimic conditions in the oral cavity, in biofilms. Our current understanding of phenotypic capabilities of individual and complex mixtures of adherent oral bacteria is in its infancy. There is ample evidence that oral streptococci have different patterns of gene expression than planktonic cells, but we have little understanding of the basis for these observations. Even in biofilmforming bacteria with very well-developed genetic systems it is only very recently that genetic loci involved in biofilm formation and responses to surface growth have been identified. A comprehensive study of the physiology and gene expression characteristics of adherent oral bacteria not only will enhance our abilities to control oral diseases, but it will provide critical information that can be applied to a variety of other pathogenic microorganisms.

[In vitro assessment of antibacterial activity of ozonized water against Staphylococcus aureus]

Staphylococcus aureus belongs to the normal flora of the skin, mucosa and nasopharynx of several animal species, including man, but it is also associated to illnesses such as abscesses, bacteremia, endocarditis and osteomyelitis, besides showing resistance to multiple drugs. The purpose of this paper was to evaluate the disinfecting ability of ozone when dissolved in water. Suspensions of Staphylococcus aureus with concentrations varying from 10(6) to 10(16) microorganisms/ml were prepared. One milliliter of each recently prepared suspension was added to 99 ml of distilled water (with or without previous ozonization) contained in a crystal reactor. Aliquots of 0.1 ml of this new suspension were taken at various time intervals and, then, serially diluted and inoculated on plaques. The data indicated that there was difference in the disinfecting effect when distilled water was used with and without previous ozonization.

Factors affecting the resting pH of in vitro human microcosm dental plaque and Streptococcus mutans biofilms

The aim was to examine factors that potentially control the resting pH, defined as the pH unaffected by meals, of microcosm dental plaques and Streptococcus mutans biofilms under standard conditions, and to examine the effect of supplying urea at concentrations found intraorally. Microcosm plaques were cultured from plaque bacteria-enriched saliva in an 'artificial mouth' with a continuous supply of a medium including 0.25% mucin [Basal Medium Mucin, (BMM), 3.6 ml/hr per plaque] and a periodic supply of sucrose. The steady-state resting pH was 6.4 (range +/- 0.1) in BMM containing no urea and supplied at the standard flowrate. This is a robust property of the ecosystem. In one experiment with a replicated (n = 9) set of measurements, the resting pH was approx. pH 6.3, 6.4, 6.7 and 7.3 with 0, 1, 5 and 20 mmol/l urea in the BMM. The magnitude of sucrose- and urea-induced pH responses was unaffected by elevating the resting pH to produce parallel pH curves. The sucrose-induced pH curves were analogous to those classically reported by Stephan that showed an association between caries activity and increasingly acidic plaque pH responses to glucose. Stopping the BMM flow caused a pH rise, indicating continuing net alkali generation from BMM components in the absence of a fluid flow. Step. mutans monoculture biofilms had an acidic resting pH of 5.0 to 5.3, which increased to 6.8 following an adventitious superinfection by Bacillus cereus. It was concluded that the resting pH in plaque results from a delicate balance between alkali and acid generation, which is in turn dependent both on the bacterial composition of the plaque and on the supply of substrates and buffers from, and metabolite clearance into, flowing oral fluid. In vivo the resting pH will vary with site-specific changing saliva flows. Urea continuously supplied at concentrations normal for saliva and gingival crevicular fluid can raise the resting pH of microcosm plaque by an amount tat in vivo would probably be significant in reducing dental caries.

Artificial dental plaque biofilm model systems

Difficulties with in vivo studies of natural plaque and its complex, heterogeneous structure have led to development of laboratory biofilm plaque model systems. Technologies for their culture are outlined, and the rationale, strengths, and relative uses of two complementary approaches to microbial models with a focus on plaque biodiversity are analyzed. Construction of synthetic consortia biofilms of major plaque species has established a variety of bacterial interactions important in plaque development. In particular, the 'Marsh' nine-species biofilm consortia systems are powerful quasi steady-state models which can be closely specified, modified, and analyzed. In the second approach, microcosm plaque biofilms are evolved in vitro from the natural oral microflora to the laboratory model most closely related to plaque in vivo. Functionally reproducible microcosm plaques are attainable with a biodiverse microbiota, heterogeneous structure, and pH behavior consistent with those of natural plaque. The resting pH can be controlled by urea supply. Their growth patterns, pH gradient formation, control of urease levels by environmental effectors, and plaque mineralization have been investigated. Microcosm biofilms may be the only useful in vitro systems where the identity of the microbes and processes involved is uncertain. Together, these two approaches begin to capture the complexity of plaque biofilm development, ecology, behavior, and pathology. They facilitate hypothesis testing across almost the whole range of plaque biology and the investigation of antiplaque procedures yielding accurate predictions of plaque behavior in vivo.