Synergistic effects of antibiotics and an N-acyl homoserine lactone analog on Porphyromonas gingivalis biofilms

Antibiofilm Properties and Demineralization Suppression in Early Enamel Lesions Using Dental Coating Materials

This study aimed to investigate the effects of dental coating materials on Streptococcus mutans biofilm formation. The test materials were PRG Barrier Coat (PRG), BioCoat Ca (BioC), and FluorDental Jelly (FluorJ). Bovine enamel specimens were demineralized to mimic early enamel lesions. The biofilm was developed on a specimen treated with one of the materials by using a modified Robbins device flow-cell system. Scanning electron and fluorescence confocal laser scanning microscopy, viable and total cell counts, and gene expression assessments of the antibiofilm were performed. Ion incorporation was analyzed using a wavelength-dispersive X-ray spectroscopy electron probe microanalyzer. All materials allowed biofilm formation but reduced its volume. FluorJ was the only material that inhibited biofilm accumulation and had a bactericidal effect, revealing 0.66 log CFU in viable cells and 1.23 log copy reduction in total cells compared with the untreated group after 24 h of incubation. The ions released from PRG varied depending on the element. BioC contributed to enamel remineralization by supplying calcium ions while blocking the acid produced from the biofilm. In summary, the dental coating materials physically prevented acid attacks from the biofilm while providing ions to the enamel to improve its mechanical properties.

An extensive description of the microbiological effects of silver diamine fluoride on dental biofilms using an oral in situ model

Silver diamine fluoride (SDF) has been long studied in laboratories, and its clinical effectiveness in the treatment and prevention of root caries has been reported. In the present study, we assessed the microbiological effects of SDF on dental biofilms grown on demineralized dentin in situ. Specifically, demineralized bovine root dentin slabs used as biofilm substrates were treated with 38% SDF, and the biofilms formed after this treatment were analyzed via real-time PCR, DEAD/LIVE cell staining, and SEM. Next, the viable cell count was determined, and microbial profiles were compared using 16S rRNA gene sequencing. Untreated slabs were used as controls. We observed significant decreases in viable cell counts (p < 0.05), number of biofilm-forming cells (p < 0.01), biofilm thickness (p < 0.01), and high proportion of dead cells with SDF treatment (p < 0.01). The microcolonies in the SDF-treated biofilms showed less complexity, and only a limited number of genera were differentially abundant between the groups. Microbial diversity index comparisons showed no significant differences between the groups with respect to treatments days (p = 0.362). Thus, SDF negatively influenced dental biofilm growth on demineralized root dentin in situ; however, its antimicrobial action did not target a specific oral taxon.

Porphyromonas gingivalis: where do we stand in our battle against this oral pathogen?

Periodontal diseases, such as gingivitis and periodontitis, are inflammatory diseases triggered by pathogenic bacteria that lead to damage of the soft tissue and bone supporting the teeth. Amongst the identified oral periodontopathogenic bacteria, Porphyromonas gingivalis is able to enhance oral dysbiosis, which is an imbalance in the beneficial commensal and periodontal pathogenic bacteria that induces chronic inflammation. Given the critical role of oral pathogenic bacteria like P. gingivalis in the pathogenesis of periodontitis, local and/or systemic antibacterial therapy has been suggested to treat this disease, especially in its severe or refractory forms. Nevertheless, the majority of the antibacterial agents currently used for the treatment of periodontal diseases are broad-spectrum, which harms beneficial bacterial species that are critical in health, inhibit the growth of pathogenic bacteria, contribute in protecting the periodontal tissues to damage and aid in its healing. Thus, the development of more effective and specific antibacterial agents is needed to control oral pathogens in a polymicrobial environment. The strategies for the development of novel antibacterial agents include natural product isolation as well as synthetic and semi-synthetic methodologies. This review presents an overview of the periodontal diseases gingivitis and periodontitis along with current antibacterial treatment options (i.e., classes of antibacterial agents and the mechanism(s) of resistance that hinder their usage) used in periodontal diseases that specifically target oral pathogens such as P. gingivalis. In addition, to help medicinal chemists gain a better understanding of potentially promising scaffolds, this review provides an in-depth coverage of the various families of small molecules that have been investigated as potential anti-P. gingivalis agents, including novel families of compounds, repositioned drugs, as well as natural products.

In Vitro Antimicrobial Susceptibility Testing of Biofilm-Growing Bacteria: Current and Emerging Methods

The antibiotic susceptibility of bacterial pathogens is typically determined based on planktonic cells, as recommended by several international guidelines. However, most of chronic infections - such as those established in wounds, cystic fibrosis lung, and onto indwelling devices - are associated to the formation of biofilms, communities of clustered bacteria attached onto a surface, abiotic or biotic, and embedded in an extracellular matrix produced by the bacteria and complexed with molecules from the host. Sessile microorganisms show significantly increased tolerance/resistance to antibiotics compared with planktonic counterparts. Consequently, antibiotic concentrations used in standard antimicrobial susceptibility tests, although effective against planktonic bacteria in vitro, are not predictive of the concentrations required to eradicate biofilm-related infections, thus leading to treatment failure, chronicization and removal of material in patients with indwelling medical devices.Meeting the need for the in vitro evaluation of biofilm susceptibility to antibiotics, here we reviewed several methods proposed in literature highlighting their advantages and limitations to guide scientists towards an appropriate choice.

Quorum sensing systems as a new target to prevent biofilm-related oral diseases

OBJECTIVE

The present study summarizes the current knowledge on the role of bacterial extracellular signaling systems, known as quorum sensing (QS), in oral biofilm formation, and on the possibility of blocking these microbial communication systems as a potential approach to prevent and treat oral infectious diseases.

METHODS

A detailed literature review of the current knowledge of QS in the oral cavity was performed, using the databases MEDLINE (through PubMed) and Web of Science.

RESULTS

Accumulating direct and indirect evidence indicates an important role of QS molecules in the oral microbial ecosystem.

CONCLUSIONS

The mechanisms regulating gene expression through bacterial communication systems constitute a promising target to control oral biofilm formation. Although cell-to-cell communication is pivotal for biofilm formation of many pathogenic bacteria, knowledge concerning microbial interactions and signaling processes within multispecies biofilms in the oral cavity is still limited.

Effect of hydraulic retention time on electricity generation using a solid plain-graphite plate microbial fuel cell anoxic/oxic process for treating pharmaceutical sewage

Treatment efficiency and electricity generation were evaluated using a solid plain-graphite plate microbial fuel cell (MFC) anoxic/oxic (A/O) process that treated pharmaceutical sewage using different hydraulic retention times (HRT). Short HRTs increased the volumetric organic loading rate, thereby reducing the MFC performance due to rapid depletion of the substrate (carbon/nitrogen source). The COD removal efficiency decreased from 96.28% at a HRT of 8 h to 90.67% at a HRT of 5 h. The removal efficiency of total nitrogen was reduced from 74.16% at a HRT of 8 h to 53.42% at a HRT of 5 h. A shorter HRT decreased the efficiency in treatment of the pharmaceutical products (PPs), which included acetaminophen, ibuprofen and sulfamethoxazole in an aerobic reactor because these antibiotic compounds inhibited the microbial activity of the aerobic activated sludge in the MFC A/O system. The average power density and coulombic efficiency values were 162.74 mW m^-2 and 7.09% at a HRT of 8 h and 29.12 mW m^-2 and 2.23% at a HRT of 5 h, respectively. The dominant bacterial species including Hydrogenophaga spp., Rubrivivax spp. and Leptothrix spp., which seem to be involved in PP biodegradation; these were identified in the MFC A/O system under all HRT conditions for the first time using next generation sequencing. Bacterial nanowires were involved in accelerating the transfer of electrons and served as mediators in the SPGRP biofilm. In conclusion, a SPGRP MFC A/O system at a HRT of 8 h gave better removal of COD, T-N and PPs, as well as generated more electricity.

New approaches to combat Porphyromonas gingivalis biofilms

In nature, bacteria predominantly reside in structured, surface-attached communities embedded in a self-produced, extracellular matrix. These so-called biofilms play an important role in the development and pathogenesis of many infections, as they are difficult to eradicate due to their resistance to antimicrobials and host defense mechanisms. This review focusses on the biofilm-forming periodontal bacterium Porphyromonas gingivalis. Current knowledge on the virulence mechanisms underlying P. gingivalis biofilm formation is presented. In addition, oral infectious diseases in which P. gingivalis plays a key role are described, and an overview of conventional and new therapies for combating P. gingivalis biofilms is given. More insight into this intriguing pathogen might direct the development of better strategies to combat oral infections.

The quorum sensing molecule N-acyl homoserine lactone produced by Acinetobacter baumannii displays antibacterial and anticancer properties

Secretory N-acyl homoserine lactones (AHLs) mediate quorum sensing (QS) in bacteria. AHLs are shown to be inhibitory for an unrelated group of bacteria and might mimic host signalling elements, thereby subverting the regulatory events in host cells. This study investigated the AHL produced by Acinetobacter baumannii and analysed its effect on other bacterial species and mammalian cells. Chemically characterized AHL had an m/z value of 325 with a molecular formula C18H31NO4 and showed its inhibitory potential against Staphylococcus aureus. Molecular docking studies identified D-alanine-D-alanine synthetase A, a cell wall synthesizing enzyme of S. aureus having a strong binding affinity towards AHL. Electron microscopy showed the disruption and sloughing off of the S. aureus cell wall when treated with AHL. In vitro experiments revealed that this bacteriostatic AHL showed time-dependent activity and induced apoptosis in cancer cell lines. This compound could be a potential structural backbone for constructing new AHL analogues against S. aureus. The findings emphasize the need to re-evaluate all previously characterized AHLs for any additional new biological functions other than QS.

Temporal dynamics of bacterial microbiota in the human oral cavity determined using an in situ model of dental biofilms

Numerous studies on oral biofilms have been performed in vitro, although it is difficult to mimic the oral environment. Here we used an in situ model to conduct a quantitative analysis and comprehensive identification of bacterial communities over time by performing deep sequencing of 16S rRNA genes. We show here that the number of viable bacteria in supragingival biofilms increased in two steps. Using scanning and transmission electron microscopy, as well as confocal laser scanning microscopy, we detected gram-positive cocci during the first 8 h. The biofilm was subsequently covered with a thick matrix-like structure composed of different bacterial morphotypes that diversified as the number of bacteria increased. Streptococcus accounted for >20% of the population until 16 h, and obligate anaerobes such as Fusobacterium, Prevotella and Porphyromonas predominated after 48 h, and this increase was statistically significant after 96 h (P<0.05). Together, our data demonstrate that an initial population of facultative anaerobic bacteria was replaced with a population of gram-negative anaerobic bacteria during oral biofilm formation. This study, therefore, contributes to a comprehensive understanding of the composition of the bacterial microbiota involved in the health of the human oral cavity.

Agents that inhibit bacterial biofilm formation

In the biofilm form, bacteria are more resistant to various antimicrobial treatments. Bacteria in a biofilm can also survive harsh conditions and withstand the host's immune system. Therefore, there is a need for new treatment options to treat biofilm-associated infections. Currently, research is focused on the development of antibiofilm agents that are nontoxic, as it is believed that such molecules will not lead to future drug resistance. In this review, we discuss recent discoveries of antibiofilm agents and different approaches to inhibit/disperse biofilms. These new antibiofilm agents, which contain moieties such as imidazole, phenols, indole, triazole, sulfide, furanone, bromopyrrole, peptides, etc. have the potential to disperse bacterial biofilms in vivo and could positively impact human medicine in the future.

Simple observation of Streptococcus mutans biofilm by scanning electron microscopy using ionic liquids

Scanning electron microscopy (SEM) has been successfully used to image biofilms because of its high resolution and magnification. However, conventional SEM requires dehydration and metal coating of biological samples before observation, and because biofilms consist mainly of water, sample dehydration may influence the biofilm structure. When coated with an ionic liquid, which is a kind of salt that exists in the liquid state at room temperature, biological samples for SEM observation do not require dehydration or metal coating because ionic liquids do not evaporate under vacuum conditions and are electrically conductive. This study investigates the ability of ionic liquids to allow SEM observation of Streptococcus mutans biofilms compared with conventional coating methods. Two hydrophilic and two hydrophobic ionic liquids, all of which are electronic conductors, are used. Compared with samples prepared by the conventional method, the ionic-liquid-treated samples do not exhibit a fibrous extracellular matrix structure and cracking on the biofilm surface. The hydrophilic ionic liquids give clearer images of the biofilm structure than those of the hydrophobic ionic liquids. This study finds that ionic liquids are useful for allowing the observation of biofilms by SEM without preparation by dehydration and metal coating.

Biofilms as "Connectors" for Oral and Systems Medicine: A New Opportunity for Biomarkers, Molecular Targets, and Bacterial Eradication

Oral health and systems medicine are intimately related but have remained, sadly, as isolated knowledge communities for decades. Are there veritable connector knowledge domains that can usefully link them together on the critical path to biomarker research and “one health”? In this context, it is noteworthy that bacteria form surface-attached communities on most biological surfaces, including the oral cavity. Biofilm-forming bacteria contribute to periodontal diseases and recent evidences point to roles of these bacteria in systemic diseases as well, with cardiovascular diseases, obesity, and cancer as notable examples. Interestingly, the combined mass of microorganisms such as bacteria are so large that when we combine all plants and animals on earth, the total biomass of bacteria is still bigger. They literally do colonize everywhere, not only soil and water but our skin, digestive tract, and even oral cavity are colonized by bacteria. Hence efforts to delineate biofilm formation mechanisms of oral bacteria and microorganisms and the development of small molecules to inhibit biofilm formation in the oral cavity is very timely for both diagnostics and therapeutics. Research on biofilms can benefit both oral and systems medicine. Here, we examine, review, and synthesize new knowledge on the current understanding of oral biofilm formation, the small molecule targets that can inhibit biofilm formation in the mouth. We suggest new directions for both oral and systems medicine, using various omics technologies such as SILAC and RNAseq, that could yield deeper insights, biomarkers, and molecular targets to design small molecules that selectively aim at eradication of pathogenic oral bacteria. Ultimately, devising new ways to control and eradicate bacteria in biofilms will open up novel diagnostic and therapeutic avenues for oral and systemic diseases alike.

Promotion of endodontic lesions in rats by a novel extraradicular biofilm model using obturation materials

Although extraradicular biofilm formation is related to refractory periapical periodontitis, the mechanism of extraradicular biofilm development, as well as its effect on periapical lesions, is unknown. Therefore, we aimed to develop an in vivo extraradicular biofilm model in rats and to identify and quantify extraradicular biofilm-forming bacteria while investigating the effect of extraradicular biofilms on periapical lesions. Periapical lesions were induced by exposing the pulpal tissue of the mandibular first molars of male Wistar rats to their oral environment. Four weeks later, gutta-percha points were excessively inserted into the mesial root canals of the right first molars (experimental sites) but not the left first molars (control sites). After 6 and 8 weeks of pulp exposure, the presence of extraradicular biofilms was confirmed histomorphologically, and biofilm-forming bacteria were identified by using classical culture methods. The biofilms were observed in the extraradicular area of the experimental sites. Similar species were detected both inside and outside the root canals. The bacterial count, quantified by real-time PCR assays, in the extraradicular area gradually increased in the experimental sites until 20 weeks after pulp exposure. After 8 weeks of pulp exposure, the periapical lesion volume that was measured by micro-computed tomography was significantly larger in the experimental sites than in the control sites (P < 0.05 by Welch's t test). These results suggest that we developed an extraradicular biofilm model in rats and that extraradicular biofilms affect developing periapical lesions.

Effects of the tea catechin epigallocatechin gallate on Porphyromonas gingivalis biofilms

AIMS

The aim of this study was to investigate the effects of tea catechin epigallocatechin gallate (EGCg) on established biofilms and biofilm formation by Porphyromonas gingivalis, a major pathogen of periodontal disease.

METHODS AND RESULTS

Biofilm cell survival was measured using adenosine triphosphate (ATP) bioluminescence. In the presence of EGCg, the ATP level in cells of established biofilms was significantly decreased compared to the controls (P < 0·0001). Transmission electron microscopy revealed that EGCg damaged the cell membrane and cell wall of P. gingivalis. Confocal laser-scanning microscopy revealed that the proportion of dead cells was higher in biofilms treated with EGCg. Moreover, the effects of subminimal inhibitory concentrations (MICs) of EGCg on P. gingivalis biofilm formation were dose-dependent (P < 0·0001).

CONCLUSION

Our results suggest that EGCg destroys established P. gingivalis biofilms and inhibits biofilm formation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Development of chemical control agents against oral biofilms is necessary, because oral biofilms can be only removed using mechanical debridement. This article indicates that EGCg may represent a novel antibiofilm agent that prevents infections involving bacterial biofilms such as periodontitis.

The sinR ortholog PGN_0088 encodes a transcriptional regulator that inhibits polysaccharide synthesis in Porphyromonas gingivalis ATCC 33277 biofilms

Biofilm-forming cells are distinct from well characterized planktonic cells and aggregate in the extracellular matrix, the so-called extracellular polymeric substances (EPS). The sinR gene of Bacillus subtilis encodes a transcriptional regulator that is known to be involved in the biosynthesis of EPS in biofilms. Porphyromonas gingivalis inhabits the subgingival and extraradicular biofilm of humans and is one of the primary pathogens that cause progressive marginal and refractory apical periodontitis. Furthermore, P. gingivalis possesses PGN_0088, which encodes a putative ortholog of B. subtilis sinR. Here, we investigated the role of PGN_0088 (sinR) on biofilm formation. P. gingivalis strains formed biofilms on saliva-coated glass surfaces in phosphate buffered saline. Quantitative analysis indicated that the biofilm of the sinR null mutant consisted of dense exopolysaccharide. Microscopic observations showed that the increased levels of exopolysaccharide produced by the sinR mutant changed the morphology of the EPS to a mesh-liked structure. Furthermore, physical analyses suggested that the enrichment of exopolysaccharide in the EPS enhanced the resistance of the biofilm to hydrodynamic shear force. The results presented here demonstrate sinR plays important roles in the ability of P. gingivalis strain ATCC 33277 to act as a negative mediator of exopolysaccharide accumulation and is indirectly associated with the structure of the EPS and the force of its adhesion to surfaces.