Dental Biofilm and Laboratory Microbial Culture Models for Cariology Research

Remineralising enamel caries with a novel peptide: An in vitro study

OBJECTIVE

To evaluate the antibacterial and remineralising effects of GAPI peptide on artificial enamel caries.

METHODS

Human enamel blocks were exposed to Streptococcus mutans biofilm to create artificial carious lesions. The blocks were randomly assigned to either the GAPI treatment group or the deionised water control group, treated twice daily for 21 days. The viability, growth kinetics, and morphology of S. mutans biofilms were assessed using confocal laser scanning microscopy (CLSM), colony-forming unit (CFU) counting, and scanning electron microscopy (SEM). Lesion depth, mineral loss, calcium-to-phosphorus ratio, Knoop hardness, enamel surface morphology, and crystal characteristics of enamel lesions were determined using micro-computed tomography (Micro-CT), SEM-energy dispersive spectroscopy (EDS), a microhardness tester, SEM, and X-ray diffraction (XRD).

RESULTS

CLSM showed that the dead-to-live ratio of S. mutans was 0.8 ± 0.1 in the GAPI group and 0.4 ± 0.1 in the control group (p < 0.001). The Log CFUs were 6.9 ± 0.7 in the GAPI group and 8.1 ± 0.5 in the control group (p = 0.002). SEM revealed confluent growth of S. mutans in the control group but not in the GAPI group, which also exhibited cell damage. Micro-CT showed that the lesion depth (µm) was 142 ± 11 in the GAPI group and 178 ± 20 in the control group (p < 0.001), with mineral loss (gcm⁻³) of 1.1 ± 0.1 and 1.5 ± 0.1, respectively (p < 0.001). SEM-EDS indicated that the calcium-to-phosphorus ratio was 1.71 ± 0.02 in the GAPI group and 1.67 ± 0.03 in the control group (p = 0.006). Additionally, Knoop hardness was 302 ± 22 in the GAPI group and 242 ± 17 in the control group (p < 0.001). SEM revealed an orderly pattern of enamel rods in the GAPI group, and XRD showed better crystallisation of hydroxyapatite in the GAPI group compared to the control group.

CONCLUSION

GAPI exhibits antibacterial and remineralising properties against artificial enamel caries.

CLINICAL SIGNIFICANCE

If the anti-caries properties of GAPI are confirmed in clinical studies, it could be used for caries prevention.

Accumulation and removal of Streptococcus mutans biofilm on enamel and root surfaces in vitro

Objective

This study aimed to quantitatively investigate the accumulation of Streptococcus mutans biofilm on enamel and root surfaces and assess the amount of biofilm removal using (1) experimental toothpaste and (2) water, in a closed system of flow chamber.

Methods

Eight sound premolars were embedded in epoxy resin and polished with silicon carbide grinding papers to display enamel and root surfaces. To mimic biofilm, cultures of Streptococcus mutans were prepared and grown on the tooth surfaces over night before they were exposed to either 2 liters of Milli Q water or 2 liters of 40% experimental toothpaste in the flow chamber. The amount of biofilm was measured and quantified in Fluorescence microscopy. Mean fluorescence values were recorded and analysed using Microsoft® Excel® (MS Excel 2016).

Results

The ability to grow biofilm was equally present at both the enamel and root surfaces. The use of water and 40% experimental toothpaste showed a significant reduction of areas covered with biofilm on both enamel and root dentin in comparison to untreated surfaces (p < 0.01). Significantly more biofilm was removed from enamel compared to root surfaces when treated with either water and toothpaste (p < 0.01). Slightly less biofilm was removed by the use of water compared to toothpaste on both enamel and root dentin surfaces, although the differences were not statistically significant.

Conclusion

The results indicate that less biofilm is removed from the root surfaces than enamel by the use of water and 40% experimental toothpaste in flow chamber. Assessing oral biofilm accumulation and monitoring biofilm formation on enamel and root dentin surfaces give oral health professionals important directions that could strenghten the significance of dental caries prevention. Improving older individuals' oral hygiene practices should therefore be considered an important measure to prevent root caries.

In Vitro Models Used in the Formation of Root Caries Lesions-A Review of the Literature

The management of root caries remains a challenge for clinicians due to its unique anatomical location and structure. There is increasing interest in utilising artificial root caries lesions to develop new strategies for remineralisation. An ideal protocol has not yet been agreed upon. The aim of this review is to provide a structured overview of previously reported in vitro root caries models. The literature was screened and mined for information mainly on substrate selection, model systems utilised, and variables used in the models. Human roots (60%) were the most frequently used substrates, followed by bovine roots (40%). Chemical models (69%) were the most frequently utilised model systems, followed by microbiological models (27%), to form root caries lesions. Acetate buffer solution (80%), pH 5.0 or above (40%), and a demineralisation time of five days (25%) were the common variables used in the chemical systems, while mono-species biofilm was most frequently used (73%) in microbiological models and Streptococcus mutans was the most common bacterial strain utilised in these models (80%). This review highlights the variability amongst the experimental approaches, discusses the advantages and limitations of these approaches, and emphasises that standardisation of experimental conditions along with sustained research will benefit root caries research.

Effect of silver diamine fluoride upon the microbial community of carious lesions: A scoping review

OBJECTIVES

To explore the effects of silver diamine fluoride (SDF) on the microbial community of carious lesions.

DATA

Original studies evaluating the effect of SDF treatment on the microbial community of human carious lesions were included.

SOURCES

A systematic search of English-language publications was performed in PubMed, EMBASE, Scopus, and Web of Science. Gray literature was searched in ClinicalTrials.gov and Google Scholar.

STUDY SELECTION/RESULTS

This review included seven publications reporting the effects of SDF on microbial community of dental plaque or carious dentin, including the microbial biodiversity, relative abundance of microbial taxa, and predicted functional pathways of the microbial community. The studies on microbial community of dental plaque reported that SDF did not have a significant effect on both the within-community species diversity (alpha-diversity) and inter-community microbial compositional dissimilarity (beta-diversity) of the plaque microbial communities. However, SDF changed the relative abundance of 29 bacterial species of plaque community, inhibited carbohydrate transportation and interfered with the metabolic functions of the plaque microbial community. A study on the microbial community in dentin carious lesions reported that SDF affected its beta-diversity and changed the relative abundance of 14 bacterial species.

CONCLUSION

SDF showed no significant effects on the biodiversity of the plaque microbial community but changed the beta-diversity of the carious dentin microbial community. SDF could change the relative abundance of certain bacterial species in the dental plaque and the carious dentin. SDF could also affect the predicted functional pathways of the microbial community.

CLINICAL SIGNIFICANCE

This review provided comprehensive evidence on the potential effect of SDF treatment on the microbial community of carious lesions.

A novel glass ionomer cement with silver zeolite for restorative dentistry

OBJECTIVE

To develop an antimicrobial silver zeolite glass ionomer cement (SZ-GIC) and determine its biocompatibility, physical, adhesive and antibacterial properties.

METHODS

Silver nitrate and sodium zeolite were used to synthesize silver zeolite (SZ). SZ-GICs were prepared by incorporating SZ into GIC at 5% (SZ-GIC5), 2% (SZ-GIC2), or 1% (SZ-GIC1) by weight, respectively. The SZ-GICs were characterized by evaluating surface morphology, topography and elemental composition. SZ-GICs' biocompatibility was assessed by evaluating cell cytotoxicity. Their physical properties were determined by testing setting time, compressive strength, flexural strength, water sorption and solubility. Their adhesive property was assessed by evaluating micro-tensile bond strength. Their antibacterial properties were assessed by evaluating biofilm growth kinetic, metabolic activity, viability and morphology. GIC was used as a control.

RESULTS

SZ was a three-dimensional crystalline mineral. SZ-GICs (including SZ-GIC 5, 2 and 1) showed similar surface morphology and topography to GIC. SZ-GIC1 and GIC had no difference in cell cytotoxicity (p>0.05). SZ-GICs and GIC showed no difference in setting time (p>0.05). SZ-GICs had higher compressive and flexural strength than GIC (p<0.05). SZ-GIC2 and SZ-GIC1 showed lower water sorption and solubility than GIC (p<0.05). SZ-GICs had higher micro-tensile bond strength than GIC (p<0.05). Biofilms on SZ-GICs' surfaces showed lower colony-forming units, decreased metabolic activities, higher percentages of dead cells and more ruptured bacterial cells compared with those on GIC.

CONCLUSION

SZ-GIC with silver zeolite at 1% by weight are as biocompatible as conventional GIC. The SZ-GICs have enhanced physical, adhesive and antibacterial properties than GIC.

CLINICAL SIGNIFICANCE

A silver zeolite glass ionomer cement was developed. The SZ-GICs have great potential for caries prevention and management.

Magnitude, associated factors, and antimicrobial susceptibility pattern of bacterial isolates among adult dental caries patients attending Hiwot Fana comprehensive specialized university hospital, Harar, Eastern Ethiopia

BACKGROUND

Dental caries is defined as a dynamic diet microbial disease of teeth, which results in localized dissolution and destruction of the mineralized tissues of the teeth. Dental caries develops when there is a susceptible tooth exposed to pathogenic bacteria in the presence of substrate. Under these conditions, the bacteria metabolize substrate to form acid, which decalcifies teeth. Dental caries is among the top oral health problem in both developing and developed nations affecting around 20-50% of the population globally.

OBJECTIVE

This study was conducted to assess the magnitude, associated factors, and antimicrobial susceptibility pattern of bacterial isolates among adult dental caries patients visiting Hiwot Fana specialized university hospital dental clinic from April 23 to-June 23, 2021.

METHODS

An institutional-based cross-sectional study was conducted among 290 study participants. Convenient sampling techniques were used to select the study participants. Data was entered into Epi-info version 7.2.4.0 and exported to Statistical Package for the Social Sciences version 20 for analysis. The result was explained by using summary measures of texts, tables, and graphs after analysis by using bivariate and multivariate logistic regression. Statistical significance was defined at a p-value of less than 0.05.

RESULT

The overall magnitude of bacteria among dental caries patients was 68.3%. S mutans 74(37.4%) and Lactobacillus spp 58(29.3%) were the most predominant isolated bacteria. Lack of teeth brushing (AOR: 2.8, 95% CI:1.6, 4.6), the habit of chewing khat always (AOR:4.8, 95%CI:2.10,8.80), the habit of chewing khat sometimes (AOR: 3.8: 95% CI: 2.520,9.48) and consumption of soft drinks (AOR: 1.9, 95% CI:1.2,3.1) were significantly associated with bacterial dental caries. Almost, all bacterial isolates were susceptible to ceftriaxone and ciprofloxacin compared to Amoxicillin, Azithromycin, chloramphenicol, clindamycin, doxycycline, erythromycin, gentamycin, penicillin, tetracycline, vancomycin and tobramycin.

CONCLUSION

Teeth brushing habit, consumption of soft drink and a habit of chewing khat affects dental health and they are associated with bacterial dental caries. Harari regional health bureau better to focus by giving health education to the community about dental caries based on identified associated factors with dental caries.

Development of In Vitro and Ex Vivo Biofilm Models for the Assessment of Antibacterial Fibrous Electrospun Wound Dressings

Increasing evidence suggests that the chronicity of wounds is associated with the presence of bacterial biofilms. Therefore, novel wound care products are being developed, which can inhibit biofilm formation and/or treat already formed biofilms. A lack of standardized assays for the analysis of such novel antibacterial drug delivery systems enhances the need for appropriate tools and models for their characterization. Herein, we demonstrate that optimized and biorelevant in vitro and ex vivo wound infection and biofilm models offer a convenient approach for the testing of novel antibacterial wound dressings for their antibacterial and antibiofilm properties, allowing one to obtain qualitative and quantitative results. The in vitro model was developed using an electrospun (ES) thermally crosslinked gelatin-glucose (GEL-Glu) matrix and an ex vivo wound infection model using pig ear skin. Wound pathogens were used for colonization and biofilm development on the GEL-Glu matrix or pig skin with superficial burn wounds. The in vitro model allowed us to obtain more reproducible results compared with the ex vivo model, whereas the ex vivo model had the advantage that several pathogens preferred to form a biofilm on pig skin compared with the GEL-Glu matrix. The in vitro model functioned poorly for Staphylococcus epidermidis biofilm formation, but it worked well for Escherichia coli and Staphylococcus aureus, which were able to use the GEL-Glu matrix as a nutrient source and not only as a surface for biofilm growth. On the other hand, all tested pathogens were equally able to produce a biofilm on the surface of pig skin. The developed biofilm models enabled us to compare different ES dressings [pristine and chloramphenicol-loaded polycaprolactone (PCL) and PCL-poly(ethylene oxide) (PEO) (PCL/PEO) dressings] and understand their biofilm inhibition and treatment properties on various pathogens. Furthermore, we show that biofilms were formed on the wound surface as well as on a wound dressing, indicating that the demonstrated methods mimic well the in vivo situation. Colony forming unit (CFU) counting and live biofilm matrix as well as bacterial DNA staining together with microscopic imaging were performed for biofilm quantification and visualization, respectively. The results showed that both wound biofilm models (in vitro and ex vivo) enabled the evaluation of the desired antibiofilm properties, thus facilitating the design and development of more effective wound care products and screening of various formulations and active substances.

Antibacterial activity, cytocompatibility, and thermomechanical stability of Ti40Zr10Cu36Pd14 bulk metallic glass

This paper envisions Ti40Zr10Cu36Pd14 bulk metallic glass as an oral implant material and evaluates its antibacterial performance in the inhabitation of oral biofilm formation in comparison with the gold standard Ti-6Al-4V implant material. Metallic glasses are superior in terms of biocorrosion and have a reduced stress shielding effect compared with their crystalline counterparts. Dynamic mechanical and thermal expansion analyses on Ti40Zr10Cu36Pd14 show that these materials can be thermomechanically shaped into implants. Static water contact angle measurement on samples' surface shows an increased surface wettability on the Ti-6Al-4V surface after 48 ​h incubation in the water while the contact angle remains constant for Ti40Zr10Cu36Pd14. Further, high-resolution transmission and scanning transmission electron microscopy analysis have revealed that Ti40Zr10Cu36Pd14 interior is fully amorphous, while a 15 ​nm surface oxide is formed on its surface and assigned as copper oxide. Unlike titanium oxide formed on Ti-6Al-4V, copper oxide is hydrophobic, and its formation reduces surface wettability. Further surface analysis by X-ray photoelectron spectroscopy confirmed the presence of copper oxide on the surface. Metallic glasses cytocompatibility was first demonstrated towards human gingival fibroblasts, and then the antibacterial properties were verified towards the oral pathogen Aggregatibacter actinomycetemcomitans responsible for oral biofilm formation. After 24 ​h of direct infection, metallic glasses reported a >70% reduction of bacteria viability and the number of viable colonies was reduced by ∼8 times, as shown by the colony-forming unit count. Field emission scanning electron microscopy and fluorescent images confirmed the lower surface colonization of metallic glasses in comparison with controls. Finally, oral biofilm obtained from healthy volunteers was cultivated onto specimens' surface, and proteomics was applied to study the surface property impact on species composition within the oral plaque.

Quorum quenching of Streptococcus mutans via the nano-quercetin-based antimicrobial photodynamic therapy as a potential target for cariogenic biofilm

Background

Quorum sensing (QS) system can regulate the expression of virulence factors and biofilm formation in Streptococcus mutans. Antimicrobial photodynamic therapy (aPDT) inhibits quorum quenching (QQ), and can be used to prevent microbial biofilm. We thereby aimed to evaluate the anti-biofilm potency and anti-metabolic activity of nano-quercetin (N-QCT)-mediated aPDT against S. mutans. Also, in silico evaluation of the inhibitory effect of N-QCT on the competence-stimulating peptide (CSP) of S. mutans was performed to elucidate the impact of aPDT on various QS-regulated genes.

Methods

Cytotoxicity and intracellular reactive oxygen species (ROS) generation were assessed following synthesis and confirmation of N-QCT. Subsequently, the minimum biofilm inhibitory concentration (MBIC) of N-QCT against S. mutans and anti-biofilm effects of aPDT were assessed using colorimetric assay and plate counting. Molecular modeling and docking analysis were performed to confirm the connection of QCT to CSP. The metabolic activity of S. mutans and the expression level of various genes involved in QS were evaluated by flow cytometry and reverse transcription quantitative real-time PCR, respectively.

Results

Successful synthesis of non-toxic N-QCT was confirmed through several characterization tests. The MBIC value of N-QCT against S. mutans was 128 μg/mL. Similar to the crystal violet staining, the results log₁₀ CFU/mL showed a significant degradation of preformed biofilms in the group treated with aPDT compared to the control group (P < 0.05). Following aPDT, metabolic activity of S. mutans also decreased by 85.7% (1/2 × MBIC of N-QCT) and 77.3% (1/4 × MBIC of N-QCT), as compared to the control values (P < 0.05). In silico analysis showed that the QCT molecule was located in the site formed by polypeptide helices of CSP. The relative expression levels of the virulence genes were significantly decreased in the presence of N-QCT-mediated aPDT (P < 0.05).

Conclusions

The combination of N-QCT with blue laser as a QQ-strategy leads to maximum ROS generation, disrupts the microbial biofilm of S. mutans, reduces metabolic activity, and downregulates the expression of genes involved in the QS pathway by targeting genes of the QS signaling system of S. mutans.

Biofilm reactor calibration for in vitro investigation of composite biodegradation

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

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

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

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

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

Effect of high-fluoride dentifrice on root dentine and bacterial composition in a multispecies biofilm model

The present study evaluated the effect of high-fluoride dentifrice on dentine demineralization and bacterial composition in a multispecies biofilm model in vitro. A seven-organism bacterial consortium was grown on bovine dentine discs in a high-throughput active attachment model. The biofilms were submitted twice per day to the following dentifrices treatments: 5,000 ppm F, 1,100 ppm F, with placebo as a negative control. After 5 days of biofilm growth, dentine samples were assessed by transversal microradiography, the biofilm was collected for bacterial counts and the pH of the media was determined. Lower integrated mineral loss values were observed when 5,000 ppm F-treatment was used compared to the other treatments. Overall microbiological counts decreased with increasing F-concentration as well the pH of the media throughout the experiment. The 5,000 ppm F-treatment caused a shift in microbial composition and reduced dentine demineralization in the in-vitro experimental model.

Metataxonomic and metabolomic evidence of biofilm homeostasis disruption related to caries: an in vitro study

The ecological dysbiosis of a biofilm includes not only bacterial changes but also changes in their metabolism. Related to oral biofilms, changes in metabolic activity are crucial endpoint, linked directly to the pathogenicity of oral diseases. Despite the advances in caries research, detailed microbial and metabolomic etiology is yet to be fully clarified. To advance this knowledge, a meta‐taxonomic approach based on 16S rRNA gene sequencing and an untargeted metabolomic approach based on an ultra‐high performance liquid chromatography‐quadrupole time‐of‐flight mass spectrometry analysis (UHPLC/Q‐TOF‐MS) were conducted. To this end, an in vitro biofilm model derived from the saliva of healthy participants were developed, under commensal and cariogenic conditions by adding sucrose as the disease trigger. The cariogenic biofilms showed a significant increase of Firmicutes phyla (p = 0.019), due to the significant increase in the genus Streptococcus (p = 0.010), and Fusobacter (p < 0.001), by increase Fusobacterium (p < 0.001) and Sphingomonas (p = 0.024), while suffered a decrease in Actinobacteria (p < 0.001). As a consequence of the shift in microbiota composition, significant extracellular metabolomics changes were detected, showed 59 metabolites of the 120 identified significantly different in terms of relative abundance between the cariogenic/commensal biofilms (Rate of change > 2 and FDR < 0.05). Forty‐two metabolites were significantly higher in abundance in the cariogenic biofilms, whereas 17 metabolites were associated significantly with the commensal biofilms, principally related protein metabolism, with peptides and amino acids as protagonists, latter represented by histidine, arginine, l‐methionine, glutamic acid, and phenylalanine derivatives.

Succession of oral bacterial colonizers on dental implant materials: An in vitro biofilm model

OBJECTIVES

Oral bacterial adhesion on dental implant materials has been extensively studied using in vitro systems but has yielded results restricted to in vitro growth patterns due to limitations in species selection, sustained fastidious anaerobe growth, and mixed culture longevity. The aim of this study was to develop an oral bacterial biofilm model consisting of colonizers representative of the oral microbiome exhibiting temporal shifts characteristic of plaque development and maturation in vivo.

METHODS

Streptococcus oralis, Actinomyces naeslundii, Aggregatibacter actinomycetemcomitans, Veillonella parvula, Fusobacterium nucleatum, and Porphyromonas gingivalis were grown in monoculture prior to combination in mixed culture. Commercially pure titanium (cpTi) and yttria-stabilized zirconia (ZrO2) disks with polished, acid-etched, or sandblasted surfaces were prepared to evaluate oral bacterial adhesion. After 6 h, 1, 3, 7, 14 and 21 days, genomic DNA from planktonic and adherent bacteria was isolated. Quantitative polymerase chain reaction (qPCR) was used to enumerate the amount and proportion of each species.

RESULTS

Early-colonizing S. oralis and A. actinomycetemcomitans, dominated after 6 h prior to secondary colonization by F. nucleatum and V. parvula in planktonic (1 day) and sessile (3 days) form. A. naeslundii maintained relatively low but stable bacterial counts throughout testing. After 14 days, late-colonizing P. gingivalis became established in mixed culture and persisted, becoming the dominant species after 21 days. The composition of adherent bacteria across all substrates was statistically similar at all timepoints with notable exceptions including lower S. oralis bacterial counts on polished cpTi (3 days).

SIGNIFICANCE

Within the present model's limitations, multispecies oral bacterial attachment is similar on surface-treated cpTi and ZrO2.

In vitro model systems for exploring oral biofilms: From single-species populations to complex multi-species communities

Numerous in vitro biofilm model systems are available to study oral biofilms. Over the past several decades, increased understanding of oral biology and advances in technology have facilitated more accurate simulation of intraoral conditions and have allowed for the increased generalizability of in vitro oral biofilm studies. The integration of contemporary systems with confocal microscopy and 16S rRNA community profiling has enhanced the capabilities of in vitro biofilm model systems to quantify biofilm architecture and analyse microbial community composition. In this review, we describe several model systems relevant to modern in vitro oral biofilm studies: the constant depth film fermenter, Sorbarod perfusion system, drip-flow reactor, modified Robbins device, flowcells and microfluidic systems. We highlight how combining these systems with confocal microscopy and community composition analysis tools aids exploration of oral biofilm development under different conditions and in response to antimicrobial/anti-biofilm agents. The review closes with a discussion of future directions for the field of in vitro oral biofilm imaging and analysis.

Clinically relevant in vitro biofilm models: A need to mimic and recapitulate the host environment

Biofilm-associated infections are difficult to treat and eradicate because of their increased antimicrobial tolerance. In vitro biofilm models have enabled the high throughput testing of an array of differing novel antimicrobials and treatment strategies. However, biofilms formed in these oftentimes basic in vitro systems do not resemble biofilms seen in vivo. As a result, translatability from the lab to the clinic is poor or limited. To improve translatability, in vitro models must better recapitulate the host environment. This review describes and critically evaluates new and innovative in vitro models that better mimic the environments of a variety of clinically important, biofilm-associated infections of the skin, oropharynx, lungs, and infections related to indwelling implants and medical devices. This review highlights that many of these models represent considerable advances in the field of biofilm research and help to translate laboratory findings into the clinical practice.

UPLC-ESI-MS/MS profiling of the underground parts of common Iris species in relation to their anti-virulence activities against Staphylococcusaureus

ETHNOPHARMACOLOGICAL RELEVANCE

The use of plant extracts and their phytochemicals as candidates for targeting the microbial resistance inhibition is increasingly focused in last decades. In Mongolian traditional medicine, Irises were long used for the treatment of bacterial infections. Irises have been used since the Ancient Egyptians.

AIM OF THE STUDY

Chemical composition and virulence inhibition potential of both polar (PF) and non-polar fractions (NPF) of three common Iris species (I. confusa, I. pseudacorus and I. germanica) were explored.

MATERIAL AND METHODS

Secondary metabolites profiling was characterized by the UPLC-HRMS/MS technique. Multi-variate data analysis was performed using Metaboanalyst 3.0. Anti-virulence inhibitory activity was evaluated via anti-haemolytic assay and Quantitative biofilm inhibition assay.

RESULTS

I. pseudacorus PF exhibited the most potent effect against S. aureus haemolytic activity. All the tested fractions from all species, except I. pseudacorus NPF, have no significant inhibition on the biofilm formation of methicillin resistant and sensitive (MRSA and MSSA) S. aureus. I. pseudacorus NPF showed potent biofilm inhibitory potential of 71.4 and 85.8% against biofilm formation of MRSA and MSSA, respectively. Metabolite profiling of the investigated species revealed ninety and forty-five metabolites detected in the PFs and NPFs, respectively. Nigricin-type, tectorigenin-type isoflavonids and xanthones allowed the discrimination of I. pseudacorus PF from the other species, highlighting the importance of those metabolites in exerting its promising activity. On the other hand, triterpene acids, iridals, triacylglycerols and ceramides represented the metabolites detected in highest abundance in I. pseudacorus NPF.

CONCLUSIONS

This is the sole map represents the secondary metabolites profiling of the PFs and NPFs of common Iris species correlating them with the potent explored Staphylococcus aureus anti-virulence activity.

Efficacy of the dual-action GA-KR12 peptide for remineralising initial enamel caries: an in vitro study

OBJECTIVE

To investigate the antibiofilm and remineralising effects of the dual-action peptide GA-KR12 on artificial enamel caries.

MATERIALS AND METHODS

Enamel blocks with artificial caries were treated with sterilised deionised water as control or GA-KR12. The blocks underwent biochemical cycling with Streptococcus mutans for 3 weeks. The architecture, viability, and growth kinetics of the biofilm were determined, respectively, by scanning electron microscopy (SEM), confocal laser scanning microscopy, and quantitative (culture colony-forming units, CFUs). The mineral loss, calcium-to-phosphorus ratio, surface morphology, and crystal characteristics of the enamel surface were determined, respectively, using micro-computed tomography, energy dispersive spectroscopy, SEM, and X-ray diffraction (XRD).

RESULTS

SEM showed confluent growth of S. mutans in the control group but not in the GA-KR12-treated group. The dead-to-live ratios of the control and GA-KR12-treated groups were 0.42 ± 0.05 and 0.81 ± 0.08, respectively (p < 0.001). The log CFUs of the control and GA-KR12-treated groups were 8.15 ± 0.32 and 6.70 ± 0.49, respectively (p < 0.001). The mineral losses of the control and GA-KR12-treated groups were 1.39 ± 0.09 gcm^-3 and 1.19 ± 0.05 gcm^-3, respectively (p < 0.001). The calcium-to-phosphorus molar ratios of the control and GA-KR12-treated groups were 1.47 ± 0.03 and 1.57 ± 0.02, respectively (p < 0.001). A uniformly remineralised prismatic pattern on enamel blocks was observed in the GA-KR12-treated but not in the control group. The hydroxyapatite in the GA-KR12-treated group was better crystallised than that in the control group.

CONCLUSION

The dual-action peptide GA-KR12 inhibited the growth of S. mutans biofilm and promoted the remineralisation of enamel caries.

CLINICAL RELEVANCE

GA-KR12 potentially is applicable for managing enamel caries.

Effectiveness of propolis in maintaining oral health: a scoping review

Background

Research has revealed that periodontal diseases are caused by inflammation that results from a dysbiosis of the oral microbiome where oral bacteria multiply into larger communities referred to as dental biofilm. To help control this overgrowth of bacteria, a variety of toothpastes, dentifrices, and mouthwashes have been developed. Although not as common in North American toothpastes, propolis as an active ingredient in dentifrices has begun to emerge, as laboratory studies have suggested it has anti-inflammatory, immunomodulatory, antioxidant, antimicrobial, and antidiabetic properties. The purpose of this scoping review was to explore the literature on the effectiveness of propolis in maintaining oral health.

Methods

This review used the following criteria: Population: studies involving healthy humans; Intervention: propolis in the form of toothpaste, dentifrice, and mouthwash; Comparison: fluoride, chlorohexidine, and placebo; Outcomes: plaque and gingival indices, improvement in oral hygiene, and inhibition of bacteria. Relevant research articles were selected from Web of Science, PubMed, MEDLINE, and Scopus databases using the search parameter "propolis[tw] AND (toothpaste*[tw] OR dentifrice*[tw] OR mouthwash*[tw])". Only original articles published after 2009 and written in the English language were included.

Results

A total of 19 original papers met the criteria and showed varying levels of success achieved with the use of propolis. It was responsible for a significant lowering of specific plaque and gingival indices, inhibited the growth of bacteria, reduced oral flora diversity, and consistently improved periodontal condition, oral hygiene, and oral health.

Conclusion

Propolis may play a role in initiating, sustaining, and maintaining oral health as its desirable properties have the potential to improve various oral hygiene related indices.

A Review of Mechano-Biochemical Models for Testing Composite Restorations

Due to the severe mechano-biochemical conditions in the oral cavity, many dental restorations will degrade and eventually fail. For teeth restored with resin composite, the major modes of failure are secondary caries and fracture of the tooth or restoration. While clinical studies can answer some of the more practical questions, such as the rate of failure, fundamental understanding on the failure mechanism can be obtained from laboratory studies using simplified models more effectively. Reviewed in this article are the 4 main types of models used to study the degradation of resin-composite restorations, namely, animal, human in vivo or in situ, in vitro biofilm, and in vitro chemical models. The characteristics, advantages, and disadvantages of these models are discussed and compared. The tooth-restoration interface is widely considered the weakest link in a resin composite restoration. To account for the different types of degradation that can occur (i.e., demineralization, resin hydrolysis, and collagen degradation), enzymes such as esterase and collagenase found in the oral environment are used, in addition to acids, to form biochemical models to test resin-composite restorations in conjunction with mechanical loading. Furthermore, laboratory tests are usually performed in an accelerated manner to save time. It is argued that, for an accelerated multicomponent model to be representative and predictive in terms of both the mode and the speed of degradation, the individual components must be synchronized in their rates of action and be calibrated with clinical data. The process of calibrating the in vitro models against clinical data is briefly described. To achieve representative and predictive in vitro models, more comparative studies of in vivo and in vitro models are required to calibrate the laboratory studies.

Remineralising dentine caries using an artificial antimicrobial peptide: An in vitro study

OBJECTIVE

To investigate the antibacterial and remineralising effects of a novel dual-action antimicrobial peptide, GA-KR12, on artificial dentine caries.

METHODS

Human dentine blocks with artificial carious lesions were allocated to two groups - Group 1: dentine blocks treated with the novel antimicrobial peptide GA-KR12 twice daily; Group 2: dentine blocks received water as the negative control. Two groups underwent Streptococcus mutan biofilm-remineralisation cycles at 37 °C for 7 days. The morphology, viability and growth kinetics of the S. mutans biofilm were evaluated by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and colony-forming unit (CFU) counting, respectively. The dentine blocks' lesion depths and mineral loss, changes in chemical structure, dentine surface morphology and crystal characteristics were determined using micro-computed tomography, Fourier transform infrared (FTIR), SEM and X-ray diffraction (XRD), respectively.

RESULTS

The surface of the dentine blocks in Group 1 was partially covered by S. mutans with damaged cell structure. Group 2 showed affluent growth of S. mutans covering the dentine surface when compared to Group 1. The dead-to-live ratio of Group 1 and Group 2 were 0.78 ± 0.01 and 0.47 ± 0.08, respectively (p < 0.001). The Log CFUs of Group 1 and Group 2 were 7.14 ± 0.30 and 8.24 ± 0.20, respectively (p < 0.001). The lesion depths of Group 1 and Group 2 were 109 ± 1 µm and 135 ± 3 µm, respectively (p < 0.001). The mineral loss of Group 1 and Group 2 were 0.59 ± 0.08 gHApcm^-3 and 0.81 ± 0.07 gHApcm^-3, respectively (p < 0.001). FTIR showed the amide I-to-hydrogen phosphate (HPO₄^2-) ratios of Group 1 and Group 2 were 0.25 ± 0.05 and 0.39 ± 0.05 (p < 0.001), respectively. SEM images showed Group 1 had less exposed dentine collagen fibres than Group 2. The XRD revealed that the hydroxyapatite in Group 1 was well crystalised.

CONCLUSION

This study demonstrated that the novel antimicrobial peptide GA-KR12 inhibited the growth of S. mutans biofilm and enhanced the remineralisation of artificial dentine caries.

Antibacterial and antibiofilm activities of cinnamon essential oil nanoemulsion against multi-species oral biofilms

Cinnamon essential oil (CEO) has antibacterial properties, but its ability to suppress the formation of multi-species oral biofilms has not been fully elucidated. This study evaluated the antibacterial and antibiofilm activities of cinnamon essential oil nanoemulsion (CEON) against oral biofilms formed using a microcosm biofilm model. The biofilms were formed on bovine enamel specimens over a 7-day period, during which all specimens were treated with one of three solutions: 5% CEON (n = 35), 0.5% cocamidopropyl betaine (n = 35), or 0.12% chlorhexidine gluconate (CHX; n = 35). Antibacterial and antibiofilm activities were determined by the red/green ratios (R/G values) of 7-day-old mature biofilms photographed with quantitative light-induced fluorescence-digital, the number of aciduric bacterial colony-forming units (CFUs) within each biofilm, and the absorbance of bacterial suspensions. One-way and repeated-measures analysis of variance were performed to compare differences among the three solutions. R/G values were lowest in the 0.12% CHX group, but not significantly differ from the 5% CEON group. The number of CFUs and absorbance were lowest in the 5% CEON group. This study showed that nanoemulsified CEO inhibited the maturation of multi-species oral biofilms and the growth of oral microorganisms in biofilms, including aciduric bacteria that cause dental caries.

LuxS quorum sensing system and biofilm formation of oral microflora: A short review article

The LuxS quorum sensing system is considered as the main system that most of the oral bacteria use to communicate in order to create biofilms. Here we identified 11 of the most important biofilm formers that utilize the LuxS system and presented current and recent information regarding this system. Though different bacterial species are able to communicate thorough the LuxS system, it was also found that cross kingdom communication can occur between bacteria and fungi and bacteria and epithelial cells. Immune response also plays and important role in mitigating the effects of biofilms. Here we identified 6 of the most important molecules that are involved in the immune response to biofilms. These immune molecules maintain the stability in the oral cavity by preventing bacteria from overwhelming the space and simultaneously minimizing the immune response in order not to cause tissue damage. Here we also discuss current research being done in order to maintain the balance in the oral cavity via inhibiting biofilm formation without eradicating oral bacteria in order to prevent the overgrowth of other organisms such as Candida albicans. One approach being used is inhibiting AI-2 intermediates which leads to lack of quorum sensing communication between bacteria through the use of intermediate analogues. Another approach that found success is the utilization of D forms of sugars where D-ribose and D-galactose have been proven to inhibit the LuxS system and subsequently preventing the process of quorum sensing leading to the reduction in biofilm formation.

In-Vitro Antibacterial and Anti-Inflammatory Effects of Surfactin-Loaded Nanoparticles for Periodontitis Treatment

Periodontitis is an inflammatory disease associated with biofilm formation and gingival recession. The practice of nanotechnology in the clinical field is increased overtime due to its potential advantages in drug delivery applications. Nanoparticles can deliver drugs into the targeted area with high efficiency and cause less damages to the tissues. In this study, we investigated the antibacterial and anti-inflammatory properties of surfactin-loaded κ-carrageenan oligosaccharides linked cellulose nanofibers (CO-CNF) nanoparticles. Three types of surfactin-loaded nanoparticles were prepared based on the increasing concentration of surfactin such as 50SNPs (50 mg surfactin-loaded CO-CNF nanoparticles), 100SNPs (100 mg surfactin-loaded CO-CNF nanoparticles), and 200SNPs (200 mg surfactin-loaded CO-CNF nanoparticles). The results showed that the nanoparticles inhibited the growth of Fusobacterium nucleatum and Pseudomonas aeruginosa. The reduction in biofilm formation and metabolic activity of the bacteria were confirmed by crystal violet and MTT assay, respectively. Besides, an increase in oxidative stress was also observed in bacteria. Furthermore, anti-inflammatory effects of surfactin-loaded CO-CNF nanoparticles was observed in lipopolysaccharide (LPS)-stimulated human gingival fibroblast (HGF) cells. A decrease in the production of reactive oxygen species (ROS), transcription factor, and cytokines were observed in the presence of nanoparticles. Collectively, these observations supported the use of surfactin-loaded CO-CNF as a potential candidate for periodontitis management.

Oral care product formulations, properties and challenges

This review explores the physical, chemical and structural properties of key components of oral care products, whilst looking at the challenges which need to be overcome to continue to improve the efficacy of oral care, and improve dental health. Oral care has been an essential part of all populations and cultures around the world for thousands of years. To maintain good oral health, dental plaque causing bacteria and malodour must be controlled whilst also strengthening and protecting the teeth to prevent dental caries. Advanced modern formulations need to provide controlled and extended release of ingredients vital for dental health. With modern day products such as toothpastes and mouthwashes, it has never been easier to maintain good oral hygiene and health, yet the incidence of dental caries is still on the rise. The complex formulations of modern toothpastes and mouthwashes makes them one of the most sophisticated pharmaceutical products on the market today. The demands of the consumer coupled with the complexity of the oral cavity make it one of the most challenging development processes.

Polyphenols of Honeybee Origin with Applications in Dental Medicine

Honeybee products are a great source of polyphenols with recognized applications in dental medicine. Although their biological mechanisms in oral diseases are not fully understood, numerous in vitro, in vivo and clinical studies have reported promising results in the prevention and treatment of oral diseases. Bioactivities, such as antibacterial, antiviral, antiparasite, anticancer, anti-inflammatory and anti-oxidant properties, recommend their future study in order to develop efficient alternatives in the management of widespread oral conditions, such as dental caries and periodontitis. The most investigated mechanisms of polyphenols in oral health rely on their ability to strengthen the dental enamel, decrease the development of dental plaque formation, inhibit the progression of dental caries and development of dental pathogens and show anti-inflammatory properties. These features recommend them as useful honeybee candidates in the management of emerging oral diseases.

Phytochemical Composition and In Vitro Biological Activity of Iris spp. (Iridaceae): A New Source of Bioactive Constituents for the Inhibition of Oral Bacterial Biofilms

The inhibition and eradication of oral biofilms is increasingly focused on the use of plant extracts as mouthwashes and toothpastes adjuvants. Here, we report on the chemical composition and the antibiofilm activity of 15 methanolic extracts of Iris species against both mono-(Pseudomonas aeruginosa, Staphylococcus aureus) and multi-species oral biofilms (Streptococcus gordonii, Veillonella parvula, Fusobacterium nucleatum subsp. nucleatum, and Actinomyces naeslundii). The phytochemical profiles of Iris pallida s.l., Iris versicolor L., Iris lactea Pall., Iris carthaliniae Fomin, and Iris germanica were determined by ultra-high performance liquid chromatography-high-resolution tandem mass spectroscopy (UHPLC-HRMS/MS) analysis, and a total of 180 compounds were identified among Iris species with (iso)flavonoid dominancy. I. pallida, I. versicolor, and I. germanica inhibited both the quorum sensing and adhesion during biofilm formation in a concentration-dependent manner. However, the extracts were less active against maturated biofilms. Of the five tested species, Iris pallida s.l. was the most effective at both inhibiting biofilm formation and disrupting existing biofilms, and the leaf extract exhibited the strongest inhibitory effect compared to the root and rhizome extracts. The cytotoxicity of the extracts was excluded in human fibroblasts. The inhibition of bacterial adhesion significantly correlated with myristic acid content, and quorum sensing inhibition correlated with the 7-β-hydroxystigmast-4-en-3-one content. These findings could be useful for establishing an effective tool for the control of oral biofilms and thus dental diseases.

Chemical Composition and Antibacterial Activities of Sumac Fruit (Rhus coriaria) Essential Oil on Dental Caries Pathogens

Introduction:

Dental caries is an infectious disease, and various microorganisms are involved in its progression. The common antibacterial agents against oral pathogens have many side effects and their excessive use cause drug resistance. Therefore, the identification of natural compounds and medicinal plants with antibacterial activity has been considered by the researchers. The Sumac (Rhus coriaria) is one of the native plants of Iran, which used as a food flavoring.

Aims & Objectives:

The aim of this study was to evaluate the antimicrobial activity of Sumac essential oil on oral pathogens, including Streptococcus mutans, Lactobacillus rhamnosus, and Actinomyces viscosus.

Materials & Methods:

In this study, the Sumac essential oil was prepared and its antibacterial activity was evaluated by disk diffusion, Minimum Inhibitory Concentration (MIC), and Minimum Bactericidal Concentration (MBC) methods on established terminology strains of S. mutans, L. rhamnosus, and A. viscosus.

Results:

The obtained results showed that the Sumac essential oil has high inhibitory effects against S. mutans, followed by L. rhamnosus and A. viscosus. The predominant compound in the Sumac essential oil was related to Beta-caryophyllene.

Conclusion:

In conclusion, Sumac essential oil has an appropriate antibacterial activity and can be used in the pharmaceutical industry to produce antibacterial agents and mouthwash, against oral infectious diseases and dental caries.

On-line profiling of volatile compounds produced in vitro by pathogenic oral bacteria

Infections by oral pathogens are one of the most common health problems worldwide. Due to the intimate connection between exhaled breath and the oral cavity, breath analysis could potentially be used to diagnose these infections. However, little is known about the volatile emissions of important oral pathogens that are connected with gingivitis and periodontitis. In this study, we have performed in vitro headspace measurements on four important oral pathogens (P. gingivalis, T. forsythia, P. intermedia and P. nigrescens) using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS). Some of the most abundant compounds produced by the bacteria include hydrogen sulphide, methanethiol, acetone, dimethylsulphide, isoprene, cyclopentanone and indole as tentatively assigned from the mass spectra. Several other abundant mass signals were recorded but the assignment of these is less certain. Some of the bacterial species can be separated from each other by the emitted volatile fingerprints. The results of this study can be used in potential development of a diagnostic breath test for oral infections. In addition, as several of the measured compounds are known to be toxic, the results point to an intriguing possibility of studying the connection between the bacterial virulence and the emitted volatile compounds.

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.

Testing Anti-Biofilm Polymeric Surfaces: Where to Start?

Present day awareness of biofilm colonization on polymeric surfaces has prompted the scientific community to develop an ever-increasing number of new materials with anti-biofilm features. However, compared to the large amount of work put into discovering potent biofilm inhibitors, only a small number of papers deal with their validation, a critical step in the translation of research into practical applications. This is due to the lack of standardized testing methods and/or of well-controlled in vivo studies that show biofilm prevention on polymeric surfaces; furthermore, there has been little correlation with the reduced incidence of material deterioration. Here an overview of the most common methods for studying biofilms and for testing the anti-biofilm properties of new surfaces is provided.

A Multispecies Biofilm In Vitro Screening Model of Dental Caries for High-Throughput Susceptibility Testing

There is a current need to develop and optimize new therapeutics for the treatment of dental caries, but these efforts are limited by the relatively low throughput of relevant in vitro models. The aim of this work was to bridge the 96-well microtiter plate system with a relevant multispecies dental caries model that could be reproducibly grown to allow for the high-throughput screening of anti-biofilm therapies. Various media and inoculum concentrations were assessed using metabolic activity, biomass, viability, and acidity assays to determine the optimal laboratory-controlled conditions for a multispecies biofilm composed of Streptococcus gordonii, Streptococcus mutans, and Candida albicans. The selected model encompasses several of the known fundamental characteristics of dental caries-associated biofilms. The 1:1 RPMI:TSBYE 0.6% media supported the viability and biomass production of mono- and multispecies biofilms best. Kinetic studies over 48 h in 1:1 RPMI:TSBYE 0.6% demonstrated a stable biofilm phase between 10 and 48 h for all mono- and multispecies biofilms. The 1:1:0.1 S. gordonii: S. mutans: C. albicans multispecies biofilm in 1:1 RPMI:TSBYE 0.6% is an excellent choice for a high-throughput multispecies model of dental caries. This high-throughput multispecies model can be used for screening novel therapies and for better understanding the treatment effects on biofilm interactions and stability.

Protective Effect of 4% Titanium Tetrafluoride Varnish on Dentin Demineralization Using a Microcosm Biofilm Model

This study evaluated the effect of titanium tetrafluoride (TiF4) varnish on the development of dentin carious lesions. Bovine root dentin samples were treated for 6 h with: (A) 4% TiF4 varnish (2.45% F); (B) 5.42% sodium fluoride (NaF) varnish (2.45% F); (C) 2% chlorhexidine (CHX) gel – positive control; (D) placebo varnish; or (E) untreated – negative control (n = 4 × biological triplicate, n = 12). Treated dentin samples were exposed to human saliva mixed with McBain saliva (1:50) for the first 8 h in 24-well plates. Thereafter, the medium was removed, and McBain saliva containing 0.2% sucrose was applied for 16 h. From days 2 to 5, McBain saliva with sucrose was replaced daily (37°C, 5% CO2). The demineralization was measured using transverse microradiography, while the effect on biofilm was analyzed using viability, extracellular polysaccharide (EPS), and lactic acid production assays. The data were statistically analyzed (p < 0.05). All treatments (fluorides and CHX) significantly reduced the biofilm viability compared to placebo varnish and negative control. However, none of them was able to reduce the colony-forming unit counting for total microorganism, total streptococci, and Streptococcus mutans. NaF significantly reduced the number of Lactobacillus sp. compared to negative control. No effect was seen on lactic acid production neither on EPS synthesis, except that CHX significantly reduced the amount of insoluble EPS. Both fluorides were able to reduce dentin demineralization compared to placebo varnish and negative control; TiF4 had a better effect in reducing mineral loss and lesion depth than NaF. Therefore, TiF4 varnish has the best protective effect on dentin carious lesion formation using this model.

What are the advantages of living in a community? A microbial biofilm perspective!

Biofilm formation is the preferred mode of growth lifestyle for many microorganisms, including bacterial and fungal human pathogens. Biofilm is a strong and dynamic structure that confers a broad range of advantages to its members, such as adhesion/cohesion capabilities, mechanical properties, nutritional sources, metabolite exchange platform, cellular communication, protection and resistance to drugs (e.g., antimicrobials, antiseptics, and disinfectants), environmental stresses (e.g., dehydration and ultraviolet light), host immune attacks (e.g., antibodies, complement system, antimicrobial peptides, and phagocytes), and shear forces. Microbial biofilms cause problems in the hospital environment, generating high healthcare costs and prolonged patient stay, which can result in further secondary microbial infections and various health complications. Consequently, both public and private investments must be made to ensure better patient management, as well as to find novel therapeutic strategies to circumvent the resistance and resilience profiles arising from biofilm-associated microbial infections. In this work, we present a general overview of microbial biofilm formation and its relevance within the biomedical context.