Monitoring of extracellular pH in young dental biofilms grown in vivo in the presence and absence of sucrose

Sweet Orange Juice Processing By-Product Extracts: A Caries Management Alternative to Chlorhexidine

Dental caries is one of the most prevalent chronic diseases globally in both children and adults. This study investigated the potential of industrial sweet orange waste extracts (ISOWE) as a substitute for chlorhexidine (CHX) in managing dental caries. First, the cytotoxicity of ISOWE (40, 80, 120 mg/mL) and CHX (0.1 and 0.2%) on buccal epithelial cells was determined. ISOWE exhibited no overall toxicity, whereas CHX strongly affected cell viability. The combination of ISOWE and CHX significantly enhanced cell proliferation compared to CHX alone. Next, the antimicrobial efficacy of ISOWE, CHX, and their combination was assessed against a 7-day complex biofilm model inoculated with oral samples from human volunteers. CHX exhibited indiscriminate antimicrobial action, affecting both pathogenic and health-associated oral microorganisms. ISOWE demonstrated lower antimicrobial efficacy than CHX but showed enhanced efficacy against pathogenic species while preserving the oral microbiome's balance. When applied to a cariogenic biofilm, the combined treatment of ISOWE with 0.1% CHX showed similar efficacy to 0.2% CHX treatment alone. Overall, the findings suggest that ISOWE is a promising natural anti-cariogenic agent with lower toxicity and enhanced selectivity for pathogenic species compared to CHX.

Determinants of Microscale pH in In Situ-Grown Dental Biofilms

Dental biofilm pH is the most important determinant of virulence for the development of caries lesions. Confocal microscopy-based pH ratiometry allows monitoring biofilm pH with high spatial resolution. Experiments performed on simplified biofilm models under static conditions identified steep pH gradients as well as localized acidogenic foci that promote enamel demineralization. The present work used pH ratiometry to perform a comprehensive analysis of the effect of whole saliva flow on the microscale pH in complex, in situ-grown 48-h and 96-h biofilms (n = 54) from 9 healthy participants. pH was monitored in 12 areas at the biofilm bottom and top, and saliva flow with film thicknesses corresponding to those in the oral cavity was provided by an additively manufactured microfluidic flow cell. Biofilm pH was correlated to the bacterial composition, as determined by 16S rRNA gene sequencing. Biofilm acidogenicity varied considerably between participants and individual biofilms but also between different areas inside one biofilm, with pH gradients of up to 2 units. pH drops were more pronounced in 96-h than in 48-h biofilms (P = 0.0121) and virtually unaffected by unstimulated saliva flow (0.8 mm/min). Stimulated flow (8 mm/min) raised average biofilm pH to near-neutral values but it did not equilibrate vertical and horizontal pH gradients in the biofilms. pH was significantly lower at the biofilm base than at the top (P < 0.0001) and lower downstream than upstream (P = 0.0046), due to an accumulation of acids along the flow path. pH drops were positively correlated with biofilm thickness and negatively with the thickness of the saliva film covering the biofilm. Bacterial community composition was significantly different between biofilms with strong and weak pH responses but not their species richness. The present experimental study demonstrates that stimulated saliva flow, saliva film thickness, biofilm age, biofilm thickness, and bacterial composition are important modulators of microscale pH in dental biofilms.

A New Device for In Situ Dental Biofilm Collection Additively Manufactured by Direct Metal Laser Sintering and Vat Photopolymerization

Dental biofilms are complex medical biofilms that cause caries, the most prevalent disease of humankind. They are typically collected using handcrafted intraoral devices with mounted carriers for biofilm growth. As the geometry of handcrafted devices is not standardized, the shear forces acting on the biofilms and the access to salivary nutrients differ between carriers. The resulting variability in biofilm growth renders the comparison of different treatment modalities difficult. The aim of the present work was to design and validate an additively manufactured intraoral device with a dental bar produced by direct metal laser sintering and vat photopolymerized inserts with standardized geometry for the mounting of biofilm carriers. Additive manufacturing reduced the production time and cost, guaranteed an accurate fit of the devices and facilitated the handling of carriers without disturbing the biofilm. Biofilm growth was robust, with increasing thickness over time and moderate inter- and intraindividual variation (coefficients of variance 0.48-0.87). The biofilms showed the typical architecture and composition of dental biofilms, as evidenced by confocal microscopy and 16S rRNA gene sequencing. Deeper inserts offering increased protection from shear tended to increase the biofilm thickness, whereas prolonged exposure to sucrose during growth increased the biofilm volume but not the thickness. Ratiometric pH imaging revealed considerable pH variation between participants and also inside single biofilms. Intraoral devices for biofilm collection constitute a new application for medical additive manufacturing and offer the best possible basis for studying the influence of different treatment modalities on biofilm growth, composition, and virulence. The Clinical Trial Registration number is: 1-10-72-193-20.

Antibiofilm Efficacies of Flavonoid-Rich Sweet Orange Waste Extract against Dual-Species Biofilms

The current study evaluated the antibacterial properties of industrial sweet orange waste extracts (ISOWEs), which are a rich source of flavonoids. The ISOWEs exhibited antibacterial activity towards the dental cariogenic pathogens Streptococcus mutans and Lactobacillus casei with 13.0 ± 2.0 and 20.0 ± 2.0 mg/mL for MIC (minimum inhibitory concentration) and 37.7 ± 1.5 and 43.3 ± 2.1 mg/mL for MBC (minimum bactericidal concentration), respectively. When evaluated in a 7-day dual-species oral biofilm model, ISOWEs dose-dependently reduced the viable bacteria count, and demonstrated strong synergistic effects when combined with the anti-septic chlorhexidine (at 0.1 and 0.2%). Similarly, confocal microscopy confirmed the anti-cariogenic properties of ISOWEs, alone and in combination with chlorhexidine. The citrus flavonoids contributed differently to these effects, with the flavones (nobiletin, tangeretin and sinensetin) demonstrating significantly lower MICs and MBCs compared to the flavanones hesperidin and narirutin. In conclusion, our study demonstrated the potential of citrus waste as a currently underutilised source of flavonoids for antimicrobial applications, such as in dental health.

Changes in oral pH before and after placing preformed metal crowns in primary dentition of Mexican children

BACKGROUND: Prefabricated metal crowns (PMCs) have been widely used in pediatric dentistry due to their great success in various clinical situations. However, it is important to know the local effects, such as changes in pH in the oral environment. OBJECTIVE: To evaluate the pH variations before and after placement of PMCs. METHODS: A quasi-experimental study (before and after) was performed with 32 pediatric patients who needed rehabilitation with PMCs at a pediatric dentistry clinic in a public university. Measurements were made using a pH potentiometer before PMC placement, one week after, and one month after placement. ANOVA and Pearson correlation were performed in SPSS. RESULTS: The average age of the participants was 5.9 ± 1.6 years, and 53.1% were female. The average pH before, one week after, and one month after crown placement was 7.46 ± 0.37, 7.00 ± 0.32, and 7.1 ± 0.19, respectively. Significant differences (p< 0.05) were observed between the three pH measurements. We found differences when comparing the basal pH values to those at one week (p= 0.001) and one month (p= 0.002). CONCLUSION: Although there were statistically significant differences in the pH change values before and after the placement of crowns, these differences may not have a clinical impact.

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

The advent of implanted medical devices has greatly improved the quality of life and increased longevity. However, infection remains a significant risk because bacteria can colonize device surfaces and form biofilms that are resistant to antibiotics and the host's immune system. Several factors contribute to this resistance, including heterogeneous biochemical and pH microenvironments that can affect bacterial growth and interfere with antibiotic biochemistry; dormant regions in the biofilm with low oxygen, pH, and metabolites; slow bacterial growth and division; and poor antibody penetration through the biofilm, which may also be regions with poor acid product clearance. Measuring pH in biofilms is thus key to understanding their biochemistry and offers potential routes to detect and treat latent infections. This review covers the causes of biofilm pH changes and simulations, general findings of metabolite-dependent pH gradients, methods for measuring pH in biofilms, effects of pH on biofilms, and pH-targeted antimicrobial-based approaches.

Real-time monitoring of mono- and dual-species biofilm formation and eradication using microfluidic platform

In a human host, bacterial Staphylococcus aureus and fungal Candida albicans pathogens form a mixed biofilm that causes severe mortality and morbidity. However, research on the formation and eradication of mixed biofilms under dynamic conditions is lacking. Thus, this study employed a microfluidic technique to analyze the real-time formation of mono- and dual-species (S. aureus and C. albicans) biofilms and noninvasive optical treatment of the established mature biofilm using 405-nm laser light. A herringbone mixer thoroughly mixed both bacterial and fungal cells in the growth media before being injected into the observation channels on the microfluidic chip. At a flow rate of 1.0 µL/min of growth media for 24 h, the bacterial biofilm coverage was up to 15% higher than that of the fungal biofilm (50% for bacteria vs. 35% for fungus). On the other hand, the dual-species biofilm yielded the highest coverage of ~ 96.5% because of the collective interaction between S. aureus and C. albicans. The number of cell proliferation events in S. aureus was higher than that of C. albicans for 12 h, which indicates that the S. aureus biofilm was developed faster than C. albicans. The novel in situ test platform showed a significant bactericidal effect (80%) of the 405-nm laser light at 1080 J/cm² towards the established S. aureus biofilm, whereas the same treatment removed approximately 69% of the mixed cells in the dual-species biofilm. This study revealed that the developed microfluidic platform could be utilized to monitor the formation of dual-species biofilms in real-time and laser-induced antimicrobial effects on dual-species biofilms.

Emerging nanotechnologies for targeting antimicrobial resistance

Antimicrobial resistance is a leading cause of mortality worldwide. Without newly approved antibiotics and antifungals being brought to the market, resistance is being developed to the ones currently available to clinicians. The reason is the applied evolutionary pressure to bacterial and fungal species due to the wide overuse of common antibiotics and antifungals in clinical practice and agriculture. Biofilms harbour antimicrobial-resistant subpopulations, which make their antimicrobial treatment even more challenging. Nanoparticle-based technologies have recently been shown to successfully overcome antimicrobial resistance in both planktonic and biofilms phenotypes. This results from the combination of novel nanomaterial research and classic antimicrobial therapies which promise to deliver a whole new generation of high-performance active nanocarrier systems. This review discusses the latest developments of promising nanotechnologies with applications against resistant pathogens and evaluates their potential and feasibility for use in novel antimicrobial therapies.

pH-Responsive Hybrid Nanoparticles for Imaging Spatiotemporal pH Changes in Biofilm-Dentin Microenvironments

Engineering highly sensitive nanomaterials to monitor spatiotemporal pH changes has rather broad applications in studying various biological systems. Intraoral/biofilm-tooth pH is the single parameter that has demonstrated accurate assessment of dental caries risk, reflecting the summative integrated outcome of the complicated interactions between three etiological factors, namely, microorganisms/biofilm, diet/carbohydrates, and tooth/saliva/host. However, there is little to no technology/system capable of accurately probing simultaneously both the micro-pH profiles in dentin tissues and acidogenic oral biofilms and examining the pathophysiologic acid attacks with high spatial/temporal resolution. Therefore, a highly sensitive pH-responsive hybrid nanoparticle (pH-NP) is developed and coupled with an ex vivo tooth-biofilm caries model to simulate and study the key cariogenic determinants/steps. The pH-NP emits two distinct fluorescences with mutually inversely proportional intensities that vary accordingly to the proximity pH and with a ratiometric output sensitivity of 13.4-fold across a broad clinically relevant pH range of 3.0-8.0. Using [H⁺], in addition to pH, to calculate the "area-under-curve" corroborates the "minimum-pH" in semiquantifying the demineralizing potential in each biofilm-dentin zones/depth. The data mechanistically elucidates a two-pronged cariogenic effect of a popular-acidic-sweet-drink, in inundating the biofilm/tooth-system with H⁺ ions from both the drink and the metabolic byproducts of the biofilm.

Physicochemical Evaluation and Antibacterial Activity of Massularia acuminata Herbal Toothpaste

Objectives

Oral hygiene, an integral part of the body's general well-being, should be maintained to prevent dental problems. This study was conducted to incorporate the ethanol extract of Massularia acuminata twigs in a formulation of herbal toothpaste and evaluate its antibacterial activity compared with a commercially available herbal toothpaste against two dental pathogens, namely, Staphylococcus aureus and Streptococcus mutans.

Materials and Methods

The content of dried M. acuminata twig was extracted using ethanol and used in the formulation of toothpaste containing 1%, 2%, 3%, 4%, and 5% M. acuminata extract. The sensory and physicochemical properties of the toothpaste were evaluated. The agar well diffusion method was used to evaluate the antibacterial susceptibility of the toothpaste against S. aureus and S. mutans. Data were analyzed using One-Way analysis of variance and Student's t-test.

Results

All toothpastes were smooth and sweet and smelled pleasant. They all had good retention ability on the bristles of toothbrush and had a pH range of 7.18-7.83. The toothpastes of the extracts of different concentration demonstrated antibacterial activities against the test organisms. The antibacterial activity of the formulated toothpastes increased significantly with an increase in the extract concentration. F5 that contained 5% extract showed the highest activity, with an inhibition zone of 19.30±0.17 mm and 12.60±0.52 mm against S. aureus and S. mutans, respectively, even when compared with the commercially available herbal toothpaste.

Conclusion

The incorporation of the M. acuminata extract in the formulation of herbal toothpaste prevented the growth of S. aureus and S. mutans. Incorporating this extract in toothpaste formulation will satisfactorily maintain oral hygiene, which is desirable to prevent dental caries and periodontal diseases.

The impact of glass ionomer cement and composite resin on microscale pH in cariogenic biofilms and demineralization of dental tissues

OBJECTIVE

Secondary caries is among the most frequent reasons for the failure of dental restorations. Glass ionomer cement (GIC) restorations have been proposed to protect the surrounding dental tissues from demineralization through the release of fluoride and by buffering the acid attack from dental biofilms. In contrast, the lack of buffering by composite resin (CR) restorations has been suggested as a promoting factor for the development of secondary caries.

METHODS

The present study employed transversal microradiography and confocal microscopy based pH ratiometry to quantify mineral loss and map microscale pH gradients inside Streptococcus mutans biofilms grown on compound specimens consisting of enamel, dentin and either GIC or CR.

RESULTS

Mineral loss in dentin was significantly lower next to GIC than next to CR, but no significant differences in local biofilm pH were observed between the two restorative materials.

SIGNIFICANCE

The cariostatic effect of GIC relies predominantly on the provision of fluoride and not on a direct buffering action. The lack of buffering by CR did not affect local biofilm pH and may therefore be of minor importance for secondary caries development.

Ratiometric imaging of extracellular pH in Streptococcus mutans biofilms exposed to different flow velocities and saliva film thicknesses

Introduction: Fluid flow has a prominent influence on the metabolism of surface-attached biofilms. Dental biofilms are covered by a thin saliva film that flows at different rates in different locations under stimulated and unstimulated conditions. Methods:The present study employed pH ratiometry to study the impact of different flow velocities, saliva film thicknesses and saliva concentrations on microscale pH developments in Streptococcus mutans biofilms of different age. Results:While saliva flow at a velocity of 0.8 mm/min (unstimulated flow) had little impact on biofilm pH, stimulated flow (8 mm/min; 80 mm/min) affected vertical pH gradients in the biofilms and raised the average pH in 48-h biofilms, but not in 72-h and 168-h biofilms. The saliva film thickness had a strong impact on biofilm pH under both static and dynamic conditions. pH drops were significantly higher in biofilms exposed to a thin saliva film (≤ 50 µm) than a thick saliva film (> 50 µm). pH drops in the biofilms were also strongly dependent on the saliva concentration and thus the buffer capacity of the salivary medium. For 48-h and 72-h biofilms, but not for 168-h biofilms, pH drops in distinct microenvironments were more pronounced when the local biofilm thickness was high.

Fluorescent nanosensors reveal dynamic pH gradients during biofilm formation

Understanding the dynamic environmental microniches of biofilms will permit us to detect, manage and exploit these communities. The components and architecture of biofilms have been interrogated in depth; however, little is known about the environmental microniches present. This is primarily because of the absence of tools with the required measurement sensitivity and resolution to detect these changes. We describe the application of ratiometric fluorescent pH-sensitive nanosensors, as a tool, to observe physiological pH changes in biofilms in real time. Nanosensors comprised two pH-sensitive fluorophores covalently encapsulated with a reference pH-insensitive fluorophore in an inert polyacrylamide nanoparticle matrix. The nanosensors were used to analyse the real-time three-dimensional pH variation for two model biofilm formers: (i) opportunistic pathogen Pseudomonas aeruginosa and (ii) oral pathogen Streptococcus mutans. The detection of sugar metabolism in real time by nanosensors provides a potential application to identify therapeutic solutions to improve oral health.

Real-time monitoring of bacterial biofilms metabolic activity by a redox-reactive nanosensors array

BACKGROUND

Bacterial biofilms are communities of surface-associated microorganisms living in cellular clusters or micro-colonies, encapsulated in a complex matrix composed of an extracellular polymeric substance, separated by open water channels that act as a circulatory system that enable better diffusion of nutrients and easier removal of metabolic waste products. The monitoring of biofilms can provide important information on fundamental biofilm-related processes. That information can shed light on the bacterial processes and enable scientists to find ways of preventing future bacterial infections. Various approaches in use for biofilm analysis are based on microscopic, spectrochemical, electrochemical, and piezoelectrical methods. All these methods provide significant progress in understanding the bio-process related to biofilm formation and eradication, nevertheless, the development of novel approaches for the real-time monitoring of biochemical, in particular metabolic activity, of bacterial species during the formation, life and eradication of biofilms is of great potential importance.

RESULTS

Here, detection and monitoring of the metabolic activity of bacterial biofilms in high-ionic-strength solutions were enabled as a result of novel surface modification by an active redox system, composed of 9,10-dihydroxyanthracene/9,10-anthraquinone, on the oxide layer of the SiNW, yielding a chemically-gated FET array. With the use of enzymatic reactions of oxidases, metabolites can be converted to H2O2 and monitored by the nanosensors. Here, the successful detection of glucose metabolites in high-ionic-strength solutions, such as bacterial media, without pre-processing of small volume samples under different conditions and treatments, has been demonstrated. The biofilms were treated with antibiotics differing in their mechanisms of action and were compared to untreated biofilms. Further examination of biofilms under antibiotic treatment with SiNW-FET devices could shed light on the bioprocess that occurs within the biofilm. Moreover, finding proper treatment that eliminates the biofilm could be examined by the novel nanosensor as a monitoring tool.

CONCLUSIONS

To summarize, the combination of redox-reactive SiNW-FET devices with micro-fluidic techniques enables the performance of rapid, automated, and real-time metabolite detection with the use of minimal sample size, noninvasively and label-free. This novel platform can be used as an extremely sensitive tool for detection and establishing medical solutions for bacterial-biofilm eradication and for finding a proper treatment to eliminate biofilm contaminations. Moreover, the sensing system can be used as a research tool for further understanding of the metabolic processes that occur within the bacterial biofilm population.

A 3D printed microfluidic flow-cell for microscopy analysis of in situ-grown biofilms

Biofilm phenomena ranging from metabolic processes to attachment, detachment and quorum sensing are influenced by the fluid flow across the biofilm. A number of commercially available flow-cells allow for microscopy analysis of laboratory biofilms under flow, but there is a lack of shear controlled microfluidic devices that accommodate biofilms grown in situ on carriers or tissue samples. Therefore, we developed a flow-cell with adjustable geometry for microscopy analysis of in situ-grown biofilm samples under shear-controlled flow. The flow-cells were designed as one-piece disposable models, 3D-printed in resin and sealed with a coverslip after insertion of the biofilm sample. As a proof of concept, we studied the impact of stimulated saliva flow on pH developments in in situ-grown dental biofilms exposed to sucrose. Under static conditions, pH dropped in the biofilms, with pronounced differences between individual biofilms, but also between different microscopic fields of view within one biofilm. pH in the top layer of the biofilms tended to be lower than pH in the bottom layer. Under conditions of stimulated saliva flow (5 mm/min), pH rose to neutral or slightly alkaline values in all biofilms, and the vertical gradients were reversed, with the biofilm bottom becoming more acidic than the top. Hence, the present work demonstrates the importance of flow for the study of pH in dental biofilms.

Plasmonic Elastic Capsules as Colorimetric Reversible pH-Microsensors

There is a crucial need for effective and easily dispersible colloidal microsensors able to detect local pH changes before irreversible damages caused by demineralization, corrosion, or biofilms occur. One class of such microsensors is based on molecular dyes encapsulated or dispersed either in polymer matrices or in liquid systems exhibiting different colors upon pH variations. They are efficient but often rely on sophisticated and costly syntheses, and present significant risks of leakage and photobleaching damages, which is detrimental for mainstream applications. Another approach consists of exploiting the distance-dependent plasmonic properties of metallic nanoparticles. Still, assembling nanoparticles into dispersible colloidal pH-sensitive sensors remains a challenge. Here, it is shown how to combine optically active plasmonic gold nanoparticles and pH-responsive thin shells into "plasmocapsules." Upon pH change, plasmocapsules swell or shrink. Concomitantly, the distance between the gold nanoparticles embedded in the polymeric matrix varies, resulting in an unambiguous color change. Billions of micron-size sensors can thus be easily fabricated. They are nonintrusive, reusable, and sense local pH changes. Each plasmocapsule is an independent reversible microsensor over a large pH range. Finally, their potential use for the detection of bacterial growth is demonstrated, thus proving that plasmocapsules are a new class of sensing materials.

Intraoral appliances for in situ oral biofilm growth: a systematic review

Background: Oral biofilms are the root cause of major oral diseases. As in vitro biofilms are not representative of the intraoral milieu, various devices have been manufactured over the years to develop Appliance Grown Oral Biofilm (AGOB). Objective: To review various intraoral appliances used to develop AGOB for microbiological analysis, and to judge the optimal means for such analyses. Design: Four databases (PubMed, Science Direct, Scopus and Medline) were searched by two independent reviewers, and articles featuring the key words 'device' OR 'splint' OR 'appliance'; 'Oral biofilm' OR 'dental plaque'; 'in vivo' OR 'in situ'; 'Microbiology' OR 'Bacteria' OR 'microbiome'; were included. The standard Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) were adopted for data gathering. Results: Of the 517 articles which met the initial inclusion criteria, 24 were deemed eligible for review. The age of the AGOB, sampled at various intervals, ranged from 30 min to 28 days. The most commonly used microbiome analytical methods were fluorescence microscopy, total cell count using conventional, and molecular tools including Next Generation Sequencing (NGS) platforms. Conclusions: No uniformly superior method for collecting AGOB could be discerned. NGS platforms are preferable for AGOB analyses.

Improved pH-ratiometry for the three-dimensional mapping of pH microenvironments in biofilms under flow conditions

Confocal microscopy-based monitoring of pH in biofilms is gaining increasing interest, as it allows for a quick assessment of horizontal pH gradients without mechanically perturbing the biofilm. Ratiometric monitoring of pH with the fluorescent dye C-SNARF-4 has been used to reliably map extracellular pH in the basal layers of biofilms, but only under static conditions. Here, we expand this methodology to measurements of vertical gradients in multispecies in vitro-grown and in situ-grown dental biofilms of different age, and to pH measurements in in vitro-grown biofilms under flow conditions. After static incubation with glucose, young in vitro-grown biofilms (30h) were more acidogenic than older biofilms (120h). However, under dynamic conditions mimicking the oral salivary flow, low pH was only preserved in older biofilms. As both types of biofilm were of similar thickness (~20 μm), these findings highlight the importance of cell density and biofilm matrix maturation for pH developments. In both in vitro-grown and in in situ-grown biofilms, horizontal and vertical pH gradients were observed. Under static conditions, the surface layer of the biofilms tended to be more acidic, whereas the bottom layer became more acidic under dynamic conditions. Compared to in vitro-grown biofilms, 120 h in situ-grown biofilms showed higher acidogenicity during static incubation. This study shows that pH ratiometry with C-SNARF-4 is well-suited to monitor extracellular pH in thin biofilms in all three dimensions. The different pH dynamics observed under static and dynamic conditions argue for the implementation of flow during real-time assessment of biofilm pH.

Self-defensive antibiotic-loaded layer-by-layer coatings: Imaging of localized bacterial acidification and pH-triggering of antibiotic release

Self-defensive antibiotic-loaded coatings have shown promise in inhibiting growth of pathogenic bacteria adhering to biomaterial implants and devices, but direct proof that their antibacterial release is triggered by bacterially-induced acidification of the immediate environment under buffered conditions remained elusive. Here, we demonstrate that Staphylococcus aureus and Escherichia coli adhering to such coatings generate highly localized acidification, even in buffered conditions, to activate pH-triggered, self-defensive antibiotic release. To this end, we utilized chemically crosslinked layer-by-layer hydrogel coatings of poly(methacrylic acid) with a covalently attached pH-sensitive SNARF-1 fluorescent label for imaging, and unlabeled-antibiotic (gentamicin or polymyxin B) loaded coatings for antibacterial studies. Local acidification of the coatings induced by S. aureus and E. coli adhering to the coatings was demonstrated by confocal-laser-scanning-microscopy via wavelength-resolved imaging. pH-triggered antibiotic release under static, small volume conditions yielded high bacterial killing efficiencies for S. aureus and E. coli. Gentamicin-loaded films retained their antibacterial activity against S. aureus under fluid flow in buffered conditions. Antibacterial activity increased with the number of polymer layers in the films. Altogether, pH-triggered, self-defensive antibiotic-loaded coatings become activated by highly localized acidification in the immediate environment of an adhering bacterium, offering potential for clinical application with minimized side-effects.

STATEMENT OF SIGNIFICANCE

Polymeric coatings were created that are able to uptake and selectively release antibiotics upon stimulus by adhering bacteria in order to understand the fundamental mechanisms behind pH-triggered antibiotic release as a potential way to prevent biomaterial-associated infections. Through fluorescent imaging studies, this work importantly shows that adhering bacteria produce highly localized pH changes even in buffer. Accordingly such coatings only demonstrate antibacterial activity by antibiotic release in the presence of adhering bacteria. This is clinically important, because ad libitum releasing antibiotic coatings usually show a burst release and have often lost their antibiotic content when bacteria adhere.

Calcium-Phosphate-Osteopontin Particles Reduce Biofilm Formation and pH Drops in in situ Grown Dental Biofilms

This 2-period crossover study investigated the effect of calcium-phosphate-osteopontin particles on biofilm formation and pH in 48-h biofilms grown in situ. Bovine milk osteopontin is a highly phosphorylated glycoprotein that has been shown to interfere with bacterial adhesion to salivary-coated surfaces. Calcium-phosphate-osteopontin particles have been shown to reduce biofilm formation and pH drops in a 5-species laboratory model of dental biofilm without affecting bacterial viability. Here, smooth surface biofilms from 10 individuals were treated ex vivo 6 times/day for 30 min with either calcium-phosphate-osteopontin particles or sterile saline. After growth, the amount of biofilm formed was determined by confocal microscopy, and pH drops upon exposure to glucose were monitored using confocal-microscopy-based pH ratiometry. A total of 160 biofilms were analysed. No adverse effects of repeated ex vivo treatment with calcium-phosphate-osteopontin particles were observed. Particle treatment resulted in a 32% lower amount of biofilm formed (p < 0.05), but large inter-individual differences could be observed. Biofilm pH was significantly higher upon particle treatment, both shortly after the addition of glucose and after 30 min of incubation with glucose (p < 0.05). Calcium-phosphate-osteopontin particles may represent a new therapeutic approach to caries control and aim at directly targeting virulence factors involved in the caries process. Further studies are required to determine the effect of particle treatment on more acidogenic/aciduric biofilms as well as the remineralizing potential of the particles.