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

Triple-modified PEEK surface via plasma treatment, polydopamine coating and chlorhexidine: Assessment of biocompatibility and antibacterial properties

OBJECTIVE

To develop and evaluate a novel surface modification strategy for polyetheretherketone (PEEK) that combines cold plasma treatment with dopamine-crosslinked chlorhexidine (CHX) to enhance both soft tissue integration and antimicrobial properties for potential dental applications.

METHODS

PEEK surfaces were modified through cold plasma treatment followed by polydopamine (PDA) coating and CHX functionalization. Surface characterization was performed by SEM, FTIR, XPS, profilometer and contact angle measurements. A 15-day CHX in vitro release test was conducted to evaluate the drug delivery profile of the modified surfaces. Biological response was evaluated through human gingival fibroblasts (HGFs) cultures, examining cell adhesion and proliferation capacity. Antimicrobial efficacy was systematically evaluated through bacterial viability, colony enumeration, biofilm formation, and adhesion analysis.

RESULTS

The P-PDA-CHX modification significantly improved surface hydrophilicity, reducing contact angles from 83.6 ± 3.1° to 24.2 ± 4.2°. Surface roughness of P-PDA-CHX (0.38 ± 0.029 μm) was significantly higher than that of the P-PDA (0.28 ± 0.048 μm) and P-CHX (0.33 ± 0.033 μm) groups (p < 0.05). Compared to unmodified surfaces, the modified surfaces demonstrated enhanced HGFs proliferation and adhesion, with cells showing improved spreading and cytoskeletal organization. The P-PDA-CHX coating exhibited sustained chlorhexidine release over 15 days and demonstrated superior antibacterial properties, significantly reducing bacterial adhesion and biofilm formation while maintaining excellent biocompatibility with HGFs.

SIGNIFICANCE

This surface modification strategy offers a promising approach for improving PEEK's biological and antibacterial properties. The combination of cold plasma treatment, PDA coating, and CHX functionalization provides a solution to enhance both cellular response and bacterial resistance, which could benefit various dental applications of PEEK materials, including customized abutments, where tissue integration and bacterial control are essential.

PMA-qPCR to quantify viable cells in multispecies oral biofilm after disinfectant treatments

Conventional quantitative real-time PCR (qPCR) amplifies DNA from viable and dead cells, which can lead to an overestimation of live bacteria. Viability qPCR aims to eliminate DNA from membrane-compromised cells through treatment with propidium monoazide (PMA). Here, we evaluated PMA-qPCR to enumerate viable cells of Actinomyces oris, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus mutans, and Veillonella dispar. Five-species oral biofilms were grown on hydroxyapatite discs for 64 h. The biofilms were exposed to 0.2 % chlorhexidine (CHX) or 3 % sodium hypochlorite (NaOCl) for 2 min, either once before cell harvest at 64 h or six times during biofilm growth. The total and single species cells were quantified by culture (CFU) and qPCR from samples with and without PMA treatment before DNA extraction. For species-specific qPCR, TaqMan assays were applied. To determine total bacteria counts, a SYBR green qPCR was established using universal degenerative primers for the conserved dnaK gene. For biofilms treated once with CHX, the addition of PMA led to a 1 to 1.6 log10 reduction in PCR counts. This closely matched CFU and PMA-qPCR counts for total bacteria and all single species, except for F. nucleatum, where PMA-qPCR detected significantly more bacteria than culture. NaOCl treatment directly affected DNA and inhibited subsequent PCR amplification, even in samples without PMA. Single treatment of biofilms with 3 % NaOCl and six-fold exposure of biofilms to disinfectants resulted in no viable cell detection by culture. However, PMA did not completely prevent PCR amplification, indicating that disinfectant efficacy measured by viability PCR could be underestimated.

Mechanistic Insight into the Anti-Bacterial/Anti-Biofilm Effects of Low Chlorhexidine Concentrations on Enterococcus faecalis-In Vitro Study

BACKGROUND

Endodontic treatment failures are often linked to the persistence of Enterococcus faecalis in the root canal system. This study aimed to investigate the antibacterial/antibiofilm mechanism of chlorhexidine (CHX), particularly at low concentrations, against E. faecalis, to improve endodontic treatment protocols.

METHODS

The antibacterial activity of CHX (0.125-20 μg/mL) was evaluated against E. faecalis ATCC 29212 using various assays, including planktonic growth inhibition, colony-forming units (CFUs), membrane permeability and potential assays, high-resolution scanning electron microscopy (HR-SEM), confocal laser scanning microscopy of biofilms, biomass and metabolic activity assays on matured biofilm, and quantitative real-time PCR for gene expression. Statistical analysis was performed using Student's t-test and ANOVA.

RESULTS

CHX demonstrated concentration-dependent inhibition of E. faecalis, significantly reducing planktonic growth and CFUs. Membrane assays showed increased permeability and depolarization, indicating damage. HR-SEM revealed morphological changes, such as pore formation, while confocal microscopy showed a reduction in biofilm mass and extracellular substances. Gene expression analysis indicated the downregulation of virulence genes and upregulation of stress response genes.

CONCLUSIONS

CHX at low concentrations disrupts E. faecalis at multiple levels, from membrane disruption to gene expression modulation, affecting mature biofilm. These findings support the refinement of endodontic disinfection protocols to reduce microbial persistence.

Microbial Dynamics in Periodontal Regeneration: Understanding Microbiome Shifts and the Role of Antifouling and Bactericidal Materials: A Narrative Review

Periodontal regeneration is a multifaceted therapeutic approach to restore the tooth-supporting structures lost due to periodontal diseases. This manuscript explores the intricate interactions between regenerative therapies and the oral microbiome, emphasizing the critical role of microbial balance in achieving long-term success. While guided tissue regeneration (GTR), bone grafting, and soft tissue grafting offer promising outcomes in terms of tissue regeneration, these procedures can inadvertently alter the oral microbial ecosystem, potentially leading to dysbiosis or pathogenic recolonization. Different grafting materials, including autografts, allografts, xenografts, and alloplasts, influence microbial shifts, with variations in the healing timeline and microbial stabilization. Biologics and antimicrobials, such as enamel matrix derivatives (EMD) and sub-antimicrobial dose doxycycline (SDD), play a key role in promoting microbial homeostasis by supporting tissue repair and reducing pathogenic bacteria. Emerging strategies, such as enzyme-based therapies and antifouling materials, aim to disrupt biofilm formation and enhance the effectiveness of periodontal treatments. Understanding these microbial dynamics is essential for optimizing regenerative therapies and improving patient outcomes. The future of periodontal therapy lies in the development of advanced materials and strategies that not only restore lost tissues but also stabilize the oral microbiome, ultimately leading to long-term periodontal health.

High-Resolution Large-Area Image Analysis Deciphers the Distribution of Salmonella Cells and ECM Components in Biofilms Formed on Charged PEDOT:PSS Surfaces

Biofilms, comprised of cells embedded in extracellular matrix (ECM), enable bacterial surface colonization and contribute to pathogenesis and biofouling. Yet, antibacterial surfaces are mainly evaluated for their effect on bacterial cells rather than the ECM. Here, a method is presented to separately quantify amounts and distribution of cells and ECM in Salmonella biofilms grown on electroactive poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS). Within a custom-designed biofilm reactor, biofilm forms on PEDOT:PSS surfaces electrically addressed with a bias potential and simultaneous recording of the resulting current. The amount and distribution of cells and ECM in biofilms are analyzed using a fluorescence-based spectroscopic mapping technique and fluorescence confocal microscopy combined with advanced image processing. The study shows that surface charge leads to upregulated ECM production, leaving the cell counts largely unaffected. An altered texture is also observed, with biofilms forming small foci or more continuous structures. Supported by mutants lacking ECM production, ECM is identified as an important target when developing antibacterial strategies. Also, a central role for biofilm distribution is highlighted that likely influences antimicrobial susceptibility in biofilms. This work provides yet a link between conductive polymer materials and bacterial metabolism and reveals for the first time a specific effect of electrochemical addressing on bacterial ECM formation.

A multifunctional silk-hyaluronic acid self-healing hydrogel laden with alternatively activated macrophage-derived exosomes reshape microenvironment of diabetic wound and accelerate healing

The impairment of phenotype switching of pro-inflammatory M1 to pro-healing M2 macrophage induced by hyperglycemic microenvironment often elevates oxidative stress, impairs angiogenesis, and leads to chronic non-healing wounds in diabetic patients. Administration of M2 macrophage-derived exosomes (M2Exo) at wound site is known to polarize M1 to M2 macrophage and can accelerate wound healing by enhancing collagen deposition, angiogenesis, and re-epithelialization. In the present study, M2Exo were conjugated with oxidized hyaluronic acid and mixed with PEGylated silk fibroin to develop self-healing Exo-gel to achieve an efficient therapy for diabetic wounds. Exo-gel depicted porous networked morphology with self-healing and excellent water retention behaviour. Fibroblast cells treated with Exo-gel showed significant uptake of M2Exo that increased their proliferation and migration in vitro. Interestingly, in a diabetic wound model of wistar rats, Exo-gel treatment induced 75 % wound closure within 7 days with complete epithelial layer regeneration by modulating cytokine levels, stimulating fibroblast-keratinocyte interaction and migration, angiogenesis, and organized collagen deposition. Taken together, this study suggests that Exo-gel depict properties of an excellent wound healing matrix and can be used as a therapeutic alternative to treat chronic non-healing diabetic wounds.

Antibiofilm Effects of Oleuropein against Staphylococcus aureus: An In Vitro Study

Staphylococcus aureus has posed a huge threat to human health and the economy. Oleuropein has antibacterial activities against various microorganisms but research on its effect on the S. aureus biofilm is limited. This research aimed to estimate the antibiofilm activities of oleuropein against S. aureus. The results suggest that the minimum inhibitory concentration of oleuropein against S. aureus ATCC 25923 was 3 mg/mL. The biomass of biofilms formed on the microplates and coverslips and the viability of bacteria were significantly reduced after the treatment with oleuropein. The scanning electron microscopy observation results indicated that the stacking thickness and density of the biofilm decreased when S. aureus was exposed to oleuropein. It had a bactericidal effect on biofilm bacteria and removed polysaccharides and proteins from mature biofilms. The effects of oleuropein on the biofilm could be explained by a reduction in bacterial secretion of extracellular polymeric substances and a change in bacterial surface hydrophobicity. Based on the above findings, oleuropein has the potential to be used against food pollution caused by S. aureus biofilms.

In vitro versus in situ biofilms for evaluating the antimicrobial effectiveness of herbal mouthrinses

For centuries, diverse mouthrinses have been applied for medicinal purposes in the oral cavity. In view of the growing resistance of oral microorganisms against conventional antimicrobial agents e.g. chlorhexidine, the implementation of alternative treatments inspired by nature has lately gained increasing interest. The aim of the present study was to compare in vitro biofilm models with in situ biofilms in order to evaluate the antimicrobial potential of different natural mouthrinses. For the in vitro study a six-species supragingival biofilm model containing A. oris, V. dispar, C. albicans, F. nucleatum, S. mutans and S. oralis was used. Biofilms were grown anaerobically on hydroxyapatite discs and treated with natural mouthrinses Ratanhia, Trybol and Tebodont. 0.9% NaCl and 10% ethanol served as negative controls, while 0.2% CHX served as positive control. After 64h hours, biofilms were harvested and quantified by cultural analysis CFU. For the in situ study, individual test splints were manufactured for the participants. After 2h and 72h the biofilm-covered samples were removed and treated with the mouthrinses and controls mentioned above. The biofilms were quantified by CFU and stained for vitality under the confocal laser scanning microscope. In the in vitro study, 0.2% CHX yielded the highest antimicrobial effect. Among all mouthrinses, Tebodont (4.708 ± 1.294 log10 CFU, median 5.279, p<0.0001) compared with 0.9% NaCl showed the highest antimicrobial potential. After 72h there was no significant reduction in CFU after 0.2% CHX treatment. Only Trybol showed a statistically significant reduction of aerobic growth of microorganisms in situ (5.331 ± 0.7350 log10 CFU, median 5.579, p<0.0209). After treatment with the positive control 0.2% CHX, a significant percentage of non-vital bacteria (42.006 ± 12.173 log10 CFU, median 42.150) was detected. To sum up, a less pronounced effect of all mouthrinses was shown for the in situ biofilms compared to the in vitro biofilms.

3D Porous Collagen Matrices-A Reservoir for In Vitro Simultaneous Release of Tannic Acid and Chlorhexidine

The treatment of wounds occurring accidentally or as a result of chronic diseases most frequently requires the use of appropriate dressings, mainly to ensure tissue regeneration/healing, at the same time as treating or preventing potential bacterial infections or superinfections. Collagen type I-based scaffolds in tandem with adequate antimicrobials can successfully fulfill these requirements. In this work, starting from the corresponding hydrogels, we prepared a series of freeze-dried atelocollagen type I-based matrices loaded with tannic acid (TA) and chlorhexidine digluconate (CHDG) as active agents with a broad spectrum of antimicrobial activity and also as crosslinkers for the collagen network. The primary aim of this study was to design an original and reliable algorithm to in vitro monitor and kinetically analyze the simultaneous release of TA and CHDG from the porous matrices into an aqueous solution of phosphate-buffered saline (PBS, pH 7.4, 37 °C) containing micellar carriers of a cationic surfactant (hexadecyltrimethylammonium bromide, HTAB) as a release environment that roughly mimics human extracellular fluids in living tissues. Around this central idea, a comprehensive investigation of the lyophilized matrices (morpho-structural characterization through FT-IR spectroscopy, scanning electron microscopy, swelling behavior, resistance against the collagenolytic action of collagenase type I) was carried out. The kinetic treatment of the release data displayed a preponderance of non-Fickian-Case II diffusion behavior, which led to a general anomalous transport mechanism for both TA and CHDG, irrespective of their concentrations. This is equivalent to saying that the release regime is not governed only by the gradient concentration of the releasing components inside and outside the matrix (like in ideal Fickian diffusion), but also, to a large extent, by the relaxation phenomena of the collagen network (determined, in turn, by its crosslinking degree induced by TA and CHDG) and the dynamic capacity of the HTAB micelles to solubilize the two antimicrobials. By controlling the degree of physical crosslinking of collagen with a proper content of TA and CHDG loaded in the matrix, a tunable, sustainable release profile can be obtained.