Effects of D-arginine on <i>Porphyromonas gingivalis</i> biofilm

Soy protein hydrolysates induce menaquinone-7 biosynthesis by enhancing the biofilm formation of Bacillus subtilis natto

Menaquinone-7 (MK-7) is a form of vitamin K2 with health-beneficial effects. A novel fermentation strategy based on combining soy protein hydrolysates (SPHs) with biofilm-based fermentation was investigated to enhance menaquinone-7 (MK-7) biosynthesis by Bacillus subtilis natto. Results showed the SPHs increased MK-7 yield by 199.4% in two-stage aeration fermentation as compared to the SP-based medium in submerged fermentation, which was related to the formation of robust biofilm with wrinkles and the enhancement of cell viability. Moreover, there was a significant correlation between key genes related to MK-7 and biofilm synthesis, and the quorum sensing (QS) related genes, Spo0A and SinR, were downregulated by 0.64-fold and 0.39-fold respectively, which promoted biofilm matrix synthesis. Meanwhile, SPHs also enhanced the MK-7 precursor, isoprene side chain, supply, and MK-7 assembly efficiency. Improved fermentation performances of bacterial cells during fermentation were attributed to abundant oligopeptides (Mw < 1 kDa) and moderate amino acids, particularly Arg, Asp, and Phe in SPHs. All these results revealed that SPHs were a potential and superior nitrogen source for MK-7 production by Bacillus subtilis natto.

Characterization and morphological methods for oral biofilm visualization: where are we nowadays?

The oral microbiome represents an essential component of the oral ecosystem whose symbiotic relationship contributes to health maintenance. The biofilm represents a state of living of microorganisms surrounding themselves with a complex and tridimensional organized polymeric support and defense matrix. The substrates where the oral biofilm adhere can suffer from damages due to the microbial community metabolisms. Therefore, microbial biofilm represents the main etiological factor of the two pathologies of dental interest with the highest incidence, such as carious pathology and periodontal pathology. The study, analysis, and understanding of the characteristics of the biofilm, starting from the macroscopic structure up to the microscopic architecture, appear essential. This review examined the morphological methods used through the years to identify species, adhesion mechanisms that contribute to biofilm formation and stability, and how the action of microbicidal molecules is effective against pathological biofilm. Microscopy is the primary technique for the morphological characterization of biofilm. Light microscopy, which includes the stereomicroscope and confocal laser microscopy (CLSM), allows the visualization of microbial communities in their natural state, providing valuable information on the spatial arrangement of different microorganisms within the biofilm and revealing microbial diversity in the biofilm matrix. The stereomicroscope provides a three-dimensional view of the sample, allowing detailed observation of the structure, thickness, morphology, and distribution of the various species in the biofilm while CLSM provides information on its three-dimensional architecture, microbial composition, and dynamic development. Electron microscopy, scanning (SEM) or transmission (TEM), allows the high-resolution investigation of the architecture of the biofilm, analyzing the bacterial population, the extracellular polymeric matrix (EPS), and the mechanisms of the physical and chemical forces that contribute to the adhesion of the biofilm to the substrates, on a nanometric scale. More advanced microscopic methodologies, such as scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HR-TEM), and correlative microscopy, have enabled the evaluation of antibacterial treatments, due to the potential to reveal the efficacy of different molecules in breaking down the biofilm. In conclusion, evidence based on scientific literature shows that established microscopic methods represent the most common tools used to characterize biofilm and its morphology in oral microbiology. Further protocols and studies on the application of advanced microscopic techniques are needed to obtain precise details on the microbiological and pathological aspects of oral biofilm.

Spatiotemporal monitoring of a periodontal multispecies biofilm model: demonstration of prebiotic treatment responses

Biofilms are complex polymicrobial communities which are often associated with human infections such as the oral disease periodontitis. Studying these complex communities under controlled conditions requires in vitro biofilm model systems that mimic the natural environment as close as possible. This study established a multispecies periodontal model in the drip flow biofilm reactor in order to mimic the continuous flow of nutrients at the air-liquid interface in the oral cavity. The design is engineered to enable real-time characterization. A community of five bacteria, Streptococcus gordonii-GFPmut3*, Streptococcus oralis-GFPmut3*, Streptococcus sanguinis-pVMCherry, Fusobacterium nucleatum, and Porphyromonas gingivalis-SNAP26 is visualized using two distinct fluorescent proteins and the SNAP-tag. The biofilm in the reactor develops into a heterogeneous, spatially uniform, dense, and metabolically active biofilm with relative cell abundances similar to those in a healthy individual. Metabolic activity, structural features, and bacterial composition of the biofilm remain stable from 3 to 6 days. As a proof of concept for our periodontal model, the 3 days developed biofilm is exposed to a prebiotic treatment with L-arginine. Multifaceted effects of L-arginine on the oral biofilm were validated by this model setup. L-arginine showed to inhibit growth and incorporation of the pathogenic species and to reduce biofilm thickness and volume. Additionally, L-arginine is metabolized by Streptococcus gordonii-GFPmut3* and Streptococcus sanguinis-pVMCherry, producing high levels of ornithine and ammonium in the biofilm. In conclusion, our drip flow reactor setup is promising in studying spatiotemporal behavior of a multispecies periodontal community.ImportancePeriodontitis is a multifactorial chronic inflammatory disease in the oral cavity associated with the accumulation of microorganisms in a biofilm. Not the presence of the biofilm as such, but changes in the microbiota (i.e., dysbiosis) drive the development of periodontitis, resulting in the destruction of tooth-supporting tissues. In this respect, novel treatment approaches focus on maintaining the health-associated homeostasis of the resident oral microbiota. To get insight in dynamic biofilm responses, our research presents the establishment of a periodontal biofilm model including Streptococcus gordonii, Streptococcus oralis, Streptococcus sanguinis, Fusobacterium nucleatum, and Porphyromonas gingivalis. The added value of the model setup is the combination of simulating continuously changing natural mouth conditions with spatiotemporal biofilm profiling using non-destructive characterization tools. These applications are limited for periodontal biofilm research and would contribute in understanding treatment mechanisms, short- or long-term exposure effects, the adaptation potential of the biofilm and thus treatment strategies.

High glucose levels contribute to vascular fibrosis via the activation of the endothelial-to-mesenchymal transition in periodontitis

OBJECTIVE

To determine the changes of Porphyromonas gingivalis (P. gingivalis) growth and metabolism and identify whether the vascular epithelium change could be induced in diabetic periodontitis.

BACKGROUND

Maintaining favourable vascular function is a precondition for periodontal regeneration. In diabetic periodontitis, high glucose levels could enhance the metabolism of pathogens, and a complex condition involving inflammation and high glucose levels would disrupt homeostasis of the epithelium and promote fibrosis by endothelial-to-mesenchymal transition (EndMT).

METHODS

Porphyromonas gingivalis was cultured with glucose to judge its metabolic activity. Human umbilical vein endothelial cells (HUVECs) were treated with P. gingivalis-lipopolysaccharide (LPS) (10 μg/ml) and/or high glucose concentrations (25 mM), and transforming growth factor (TGF)-β inhibitor was used to block EndMT. Inflammation level was assessed by flow cytometry. Multiple biological functions including EndMT, angiopoiesis, and cell migration were analysed. Additionally, gene expressions and protein levels were determined with qPCR and western blot, respectively. Finally, blood vessels were cultured ex vivo, and EndMT and fibrosis markers were detected by immunohistochemistry.

RESULTS

Glucose could promote P. gingivalis growth and biofilm formation as well as the expression of virulence factor genes including FimA, RgpA, RgpB, and Kgp. P. gingivalis-LPS and glucose could increase intracellular reactive oxygen species (ROS) and promote fibrosis via EndMT in HUVECs, along with attenuating angiopoiesis and cell migration, which could be resumed by blocking EndMT with TGF-β inhibitor. Vascular fibrosis was observed after the addition of glucose via EndMT regulation.

CONCLUSION

Glucose augmented the growth and metabolism of P. gingivalis and promoted fibrosis by the activation of EndMT, as well as the inhibition of angiopoiesis and cell migration.

An ionic silver coating prevents implant-associated infection by anaerobic bacteria in vitro and in vivo in mice

Currently, implants are utilized clinically for bone transplant procedures. However, if infectious osteomyelitis occurs at implant sites, removal of bacteria can be challenging. Moreover, altered blood flow at peri-implant infectious sites can create an anaerobic environment, making it more difficult to treat infection with antibiotics. Thus, it would be beneficial if implants could be modified to exhibit antibacterial activity, even in anaerobic conditions. Here, we show antibacterial activity of silver ions coated on titanium rods, even against the anaerobic bacteria Porphyromonas gingivalis (P. gingivalis), both in vitro and in vivo. Specifically, we implanted silver-coated or control uncoated titanium rods along with P. gingivalis in mouse femoral bone BM cavities and observed significantly inhibited P. gingivalis infection with silver-coated compared with non-coated rods, based on in vivo bio-imaging. Osteonecrosis by infectious osteomyelitis and elevation of the inflammatory factors C-reactive protein and IL-6 promoted by P. gingivalis s were also significantly reduced in the presence of silver-coated rods. Overall, our study indicates that silver ion coating of an implant represents a therapeutic option to prevent associated infection, even in anaerobic conditions or against anaerobic bacteria.

New insights into the inhibitory roles and mechanisms of D-amino acids in bacterial biofilms in medicine, industry, and agriculture

Biofilms are complex aggregates of microbes that are tightly protected by an extracellular matrix (ECM) and may attach to a surface or adhere together. A higher persistence of bacteria on biofilms makes them resistant not only to harsh conditions but also to various antibiotics which led to the emergence of problems in different applications. Recently, it has been discovered that many bacteria produce and release various D-amino acids (D-AAs) to inhibit biofilm formation, which made a great deal of interest in research into the control of bacterial biofilms in diverse fields, such as human health, industrial settings, and medical devices. D-AAs have various mechanisms to inhibit bacterial biofilms such as: (i) interfering with protein synthesis (ii) Inhibition of extracellular polymeric materials (EPS) productions (protein, eDNA, and polysaccharide) (iii) Inhibition of quorum sensing (autoinducers), and (iv) interfere with peptidoglycan synthesis, these various modes of action, enables these small molecules to inhibit both Gram-negative and Gram-positive bacterial biofilms. Since most biofilms are multi-species, D-AAs in combination with other antimicrobial agents are good choices to combat a variety of bacterial biofilms without displaying toxicity on human cells. This review article addressed the role of D-AAs in controlling several bacterial biofilms and described the possible or definite mechanisms involved in this process.

D-aspartic acid protects against gingival fibroblasts inflammation by suppressing pyroptosis

BACKGROUND

Peri-implantitis is the main cause of dental implant failure, which is associated with pyroptosis. The roles of D-aspartic acid (D-Asp) on pyroptosis and the mechanism of the protective effect of D-Asp on human gingival fibroblasts (HGFs) remain unknown. This study investigated the effects of D-Asp on the pyroptosis of HGFs induced by high mobility group box 1 protein (HMGB1).

METHODS

The cytotoxic effects of D-Asp on HGFs was detected by Cell Counting Kit-8 assay, the membrane permeability was investigated by propidium iodide/ Hoechst 33,342 double staining, flow cytometry analysis, and lactate dehydrogenase releasing, The gene and protein expression levels were detected by real-time quantitative PCR, enzyme-linked immunosorbent assay, and Western blot, respectively.

RESULTS

Cell viability analysis showed that D-Asp ≤ 30 mM had no cytotoxicity to HGFs. HMGB1 drastically raised the membrane permeability of HGFs, while 1/10/30 mM D-Asp suppressed the permeability and remained the integrity of the membrane. HMGB1 promoted the mRNA expression of NLRP3, caspase-1, GSDMD, IL-1β, and IL-18, and the protein expression of IL-1β, IL-18, caspase-1, GSDMD, and NLRP3.

CONCLUSIONS

With the pretreatment of HGFs with D-Asp of 1/10/30 mM for 24 h, the cell membrane permeability was reduced and the expression of NLRP3, caspase-1, GSDMD, IL-1β, and IL-18 was significantly decreased compared with the HMGB1 group, indicating the competitive antagonism of D-Asp against HMGB1 on the binding with toll-like receptors. Hence, this study may provide a novel insight into preventing pyroptosis and propose a new strategy for the treatment of peri-implantitis.

D-arginine Enhances the Effect of Alpha-Amylase on Disassembling Actinomyces viscosus Biofilm

Peri-implantitis is the leading cause of dental implant failure, initially raised by biofilm accumulation on the implant surface. During the development of biofilm, Actinomyces viscosus (A. viscosus) plays a pivotal role in initial attachment as well as the bacterial coaggregation of multispecies pathogens. Hence, eliminating the A. viscosus-associated biofilm is fundamental for the regeneration of the lost bone around implants. Whereas clinical evidence indicated that antimicrobials and debridement did not show significant effects on the decontamination of biofilm on the implant surface. In this study, alpha-amylase was investigated for its effects on disassembling A. viscosus biofilm. Then, in order to substantially disperse biofilm under biosafety concentration, D-arginine was employed to appraise its enhancing effects on alpha-amylase. In addition, molecular dynamics simulations and molecular docking were conducted to elucidate the mechanism of D-arginine enhancing alpha-amylase. 0.1–0.5% alpha-amylase showed significant effects on disassembling A. viscosus biofilm, with definite cytotoxicity toward MC3T3-E1 cells meanwhile. Intriguingly, 8 mM D-arginine drastically enhanced the eradication of A. viscosus biofilm biomass by 0.01% alpha-amylase with biosafety in 30 min. The exopolysaccharides of biofilm were also thoroughly hydrolyzed by 0.01% alpha-amylase with 8 mM D-arginine. The biofilm thickness and integrity were disrupted, and the exopolysaccharides among the extracellular matrix were elusive. Molecular dynamics simulations showed that with the hydrogen bonding of D-arginine to the catalytic triad and calcium-binding regions of alpha-amylase, the atom fluctuation of the structure was attenuated. The distances between catalytic triad were shortened, and the calcium-binding regions became more stable. Molecular docking scores revealed that D-arginine facilitated the maltotetraose binding process of alpha-amylase. In conclusion, these results demonstrate that D-arginine enhances the disassembly effects of alpha-amylase on A. viscosus biofilm through potentiating the catalytic triad and stabilizing the calcium-binding regions, thus providing a novel strategy for the decontamination of biofilm contaminated implant surface.

Trace Element-Augmented Titanium Implant With Targeted Angiogenesis and Enhanced Osseointegration in Osteoporotic Rats

Deteriorated bone quality in osteoporosis challenges the success of implants, which are in urgent need for better early osseointegration as well as antibacterial property for long-term stability. As osteoporotic bone formation tangles with angiogenic clues, the relationship between osteogenesis and angiogenesis has been a novel therapy target for osteoporosis. However, few designs of implant coatings take the compromised osteoporotic angiogenic microenvironment into consideration. Here, we investigated the angiogenic effects of bioactive strontium ions of different doses in HUVECs only and in a co-culture system with BMSCs. A proper dose of strontium ions (0.2–1 mM) could enhance the secretion of VEGFA and Ang-1 in HUVECs as well as in the co-culture system with BMSCs, exhibiting potential to create an angiogenic microenvironment in the early stage that would be beneficial to osteogenesis. Based on the dose screening, we fabricated a bioactive titanium surface doped with zinc and different doses of strontium by plasma electrolytic oxidation (PEO), for the establishment of a microenvironment favoring osseointegration for osteoporosis. The dual bioactive elements augmented titanium surfaces induced robust osteogenic differentiation, and enhanced antimicrobial properties. Augmented titanium implant surfaces exhibited improved bone formation and bone–implant contact under comprehensive assessment of an in vivo bone–implant interface. In conclusion, zinc- and strontium-augmented titanium surface benefits the osseointegration in osteoporosis via promoting osteogenic differentiation, exerting antibacterial efficacy, and stimulating early angiogenesis.

In vitro evaluation of the antibacterial effect of colloidal bismuth subcitrate on Porphyromonas gingivalis and its biofilm

OBJECTIVE

To investigate the antibacterial and anti-biofilm effects of colloidal bismuth subcitrate (CBS) on Porphyromonas gingivalis (P. gingivalis) in its planktonic and biofilm forms and also compare it with that of 0.2% chlorhexidine (CHX).

DESIGN

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CBS were determined by the microdilution method; the bacteriostatic rate of CBS was determined by the MTT assay; the effect of CBS on the membrane integrity of P. gingivalis was investigated by the flow cytometric methods. The effects of CBS on the biomass and bacterial activity of biofilm were investigated. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to investigate the activity and structure of biofilms.

RESULTS

The MIC and MBC values were 18.75 µg/mL and 37.5 µg/mL. CBS could damage the cell membrane of P. gingivalis. CBS effectively inhibited biofilm formation and promoted dissociation at higher concentrations of 37.5 µg/mL and 75 µg/mL, respectively. The results also indicated an altered biofilm structure and reduced biofilm thickness and bacterial aggregation.

CONCLUSIONS

CBS affected the metabolic and physiological processes of P. gingivalis, inhibited the formation of biofilm, and disrupted the mature biofilm.

The Effect of Porphyromonas gingivalis Lipopolysaccharide on the Pyroptosis of Gingival Fibroblasts

Periodontitis is a chronic inflammatory disease induced by Porphyromonas gingivalis (P. gingivalis) and other pathogens. P. gingivalis release various virulence factors including lipopolysaccharide (LPS). However, whether P. gingivalis-LPS inducing pyroptosis in human gingival fibroblasts (HGFs) remains unknown. In present study, P. gingivalis-LPS decreased the membrane integrity of HGFs, and pyroptosis-associated cytokines were upregulated at the mRNA level. In addition, pyroptosis proteins were highly expressed in gingival tissues of periodontitis. P. gingivalis-LPS induced gingivitis in the rat model, and the expression level of pyroptosis-associated proteins increased. Together, P. gingivalis-LPS can activate the pyroptosis reaction, which may be a pro-pyroptosis status in a relative low concentration.

Synergistic effects of D-arginine, D-methionine and D-histidine against Porphyromonas gingivalis biofilms

Porphyromonas gingivalis biofilms are implicated in the pathology of peri-implantitis and periodontitis. In this study, D-arginine (R), D-methionine (M), D-histidine (H), and a mixture of these D-amino acids (D-AAs) were investigated as an effective therapeutic strategy against P. gingivalis biofilms. The bacterial growth activity and minimum inhibitory concentrations were determined for each D-AA, along with the effects of the D-AAs mixture on biofilm development, morphology, structure, extracellular polysaccharides (EPS), cytotoxicity towards commensals, and bacterial structure. The D-AA mixture delayed the proliferation of P. gingivalis, changed its membrane structure, and decreased biofilm thickness and integrity, as compared with individual D-AAs. The EPS content increased with the concentration of D-AAs. The present study shows that a 4 mM RMH, triple D-AA mixture, enhanced deleterious effects on P. gingivalis biofilms without any cytotoxicity compared with individual D-AAs, thus providing a new strategy for the treatment of peri-implantitis and periodontitis.

Targeting Biofilms Therapy: Current Research Strategies and Development Hurdles

Biofilms are aggregate of microorganisms in which cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS) and adhere to each other and/or to a surface. The development of biofilm affords pathogens significantly increased tolerances to antibiotics and antimicrobials. Up to 80% of human bacterial infections are biofilm-associated. Dispersal of biofilms can turn microbial cells into their more vulnerable planktonic phenotype and improve the therapeutic effect of antimicrobials. In this review, we focus on multiple therapeutic strategies that are currently being developed to target important structural and functional characteristics and drug resistance mechanisms of biofilms. We thoroughly discuss the current biofilm targeting strategies from four major aspects—targeting EPS, dispersal molecules, targeting quorum sensing, and targeting dormant cells. We explain each aspect with examples and discuss the main hurdles in the development of biofilm dispersal agents in order to provide a rationale for multi-targeted therapy strategies that target the complicated biofilms. Biofilm dispersal is a promising research direction to treat biofilm-associated infections in the future, and more in vivo experiments should be performed to ensure the efficacy of these therapeutic agents before being used in clinic.