Real-time imaging of anti-biofilm effects using CP-OCT

Yielding behaviour of chemically treated Pseudomonas fluorescens biofilms

The mechanics of biofilms are intrinsically shaped by their physicochemical environment. By understanding the influence of the extracellular matrix composition, pH and elevated levels of cationic species on the biofilm rheology, novel living materials with tuned properties can be formulated. In this study, we examine the role of a chaotropic agent (urea), two divalent cations and distilled deionized water on the nonlinear viscoelasticity of a model biofilm Pseudomonas fluorescens. The structural breakdown of each biofilm is quantified using tools of non-linear rheology. Our findings reveal that urea induced a softening response, and displayed strain overshoots comparable to distilled deionized water, without altering the microstructural packing fraction and macroscale morphology. The absorption of divalent ferrous and calcium cations into the biofilm matrix resulted in stiffening and a reduction in normalized elastic energy dissipation, accompanied by macroscale morphological wrinkling and moderate increases in the packing fraction. Notably, ferrous ions induced a predominance of rate dependent yielding, whereas the calcium ions resulted in equal contribution from both rate and strain dependent yielding and structural breakdown of the biofilms. Together, these results indicate that strain rate increasingly becomes an important factor controlling biofilm fluidity with cation-induced biofilm stiffening. The finding can help inform effective biofilm removal protocols and in development of bio-inks for additive manufacturing of biofilm derived materials.

Base type determines the effects of nucleoside monophosphates on microalgae-bacteria symbiotic systems

Microalgae are promising sources of clean energy. Bioflocculation by cocultured bacteria is an effective way to harvest microalgae. As a key foundation for microorganisms, phosphorus is theoretically effective in shaping microalgae production and flocculation. In this study, the impacts of 23 nucleoside monophosphates on Auxenochlorella pyrenoidosa growth, lipid synthesis, and self-settlement and on the symbiotic bacterial system were investigated. Adenosine monophosphate was the most effective in enhancing microalgae development (2.14-3.16 × 10⁸ cells/mL) and lipid production (average 10.48%) and resulted in a low settling velocity. Samples were divided into two groups, purine and pyrimidine feeding, according to a random forest analysis (OOB = 0%, p < 0.001). Purine feeding resulted in the highest soluble extracellular protein and polysaccharide secretion (p < 0.01). KEGG ortholog count prediction of functional genes related to biofilm formation was conducted using PICRUSt2, and significant upregulation (FC ≥ 1.77, p < 0.05) of the extracellular polymeric substance formation functional group was observed in the adenosine and guanosine treatments. The symbiotic bacterial community structure differed substantially between purine- and pyrimidine-feeding systems. In summary, these results indicated that the effect of nucleoside monophosphates on the microalgae-bacteria system is determined by the base type (purine or pyrimidine) rather than the molecular structure (cyclic or noncyclic).

Characterization of radiofrequency ablated myocardium with optical coherence tomography

Certain types of cardiac arrhythmias are best treated with radiofrequency (RF) ablation, in which an electrode is inserted into the targeted area of the myocardium and then RF electrical current is applied to heat and destroy surrounding tissue. The resulting ablation lesion usually consists of a coagulative necrotic core surrounded by a rim region of mixed viable and non-viable cells. The characterization of the RF ablated lesion is of potential clinical importance. Here we aim to elaborate optical coherence tomography (OCT) imaging for the characterization of RF-ablated myocardial tissue. In particular, the underlying principles of OCT and its polarization-sensitive counterpart (PS-OCT) are presented, followed by the knowledge needed to interpret their optical images. Studies focused on real-time monitoring of RF lesion formation in the myocardium using OCT systems are summarized. The design and development of various hybrid probes incorporating both OCT guidance and RF ablation catheters are also discussed. Finally, the challenges related to the transmission of OCT imaging systems to cardiac clinics for real-time monitoring of RF lesions are outlined.

Periodic chemical cleaning with urea: disintegration of biofilms and reduction of key biofilm-forming bacteria from reverse osmosis membranes

Biofouling is one of the major factors causing decline in membrane performance in reverse osmosis (RO) plants, and perhaps the biggest hurdle of membrane technology. Chemical cleaning is periodically carried out at RO membrane installations aiming to restore membrane performance. Typical cleaning agents used in the water treatment industry include sodium hydroxide (NaOH) and hydrochloric acid (HCl) in sequence. Rapid biofilm regrowth and related membrane performance decline after conventional chemical cleaning is a routinely observed phenomenon due to the inefficient removal of biomass from membrane modules. Since extracellular polymeric substances (EPS) make up the strongest and predominant structural framework of biofilms, disintegration of the EPS matrix should be the main target for enhanced biomass removal. Previously, we demonstrated at lab-scale the use of concentrated urea as a chemical cleaning agent for RO membrane systems. The protein denaturation property of urea was exploited to solubilize the proteinaceous foulants, weakening the EPS layer, resulting in enhanced biomass solubilization and removal from RO membrane systems. In this work, we investigated the impact of repeated chemical cleaning cycles with urea/HCl as well as NaOH/HCl on biomass removal and the potential adaptation of the biofilm microbial community. Chemical cleaning with urea/HCl was consistently more effective than NaOH/HCl cleaning over 6 cleaning and regrowth cycles. At the end of the 6 cleaning cycles, the percent reduction was 35% and 41% in feed channel pressure drop, 50% and 70% in total organic carbon, 30% and 40% in EPS proteins, and 40% and 66% in the peak intensities of protein-like matter, after NaOH/HCl cleaning and Urea/HCl cleaning, respectively. 16S ribosomal RNA (rRNA) gene sequencing of the biofilm microbial community revealed that urea cleaning does not select for key biofouling families such as Sphingomonadaceae and Xanthomonadaceae that are known to survive conventional chemical cleaning and produce adhesive EPS. This study reaffirmed that urea possesses all the desirable properties of a chemical cleaning agent, i.e., it dissolves the existing fouling layer, delays fresh fouling accumulation by inhibiting the production of a more viscous EPS, does not cause damage to the membranes, is chemically stable, and environmentally friendly as it can be recycled for cleaning.

An Eggshell-Based Toothpaste as a Cost-Effective Treatment of Dentin Hypersensitivity

Objectives This study aimed to test the efficacy of two experimentally produced eggshell-based toothpastes on dentinal tubules occlusion.

Materials and Methods Two experimental eggshell toothpastes, based on natural ingredients, with or without titanium dioxide nanoparticles (TNPs) were produced and coded “TNPs eggshell toothpaste [TNPsESTP]” or “eggshell toothpaste [ESTP],” respectively. Mid-coronal dentin discs, from 28 human extracted molar teeth, etched with 37% phosphoric acid for 60 seconds to simulate the hypersensitive dentin, were randomly divided into four groups—G1: no treatment (negative control), G2: ESTP treated, G3: TNPsESTP treated, and G4: Biorepair treated (positive control). All treated discs were brushed for 2 weeks and 1 month using a toothbrush simulator at 40 mm/s. Dentinal tubules occlusion was studied using a cross-polarization optical coherence tomography (CP-OCT) and scanning electron microscopy (SEM).

Statistical Analysis Unpaired t -test was conducted using GraphPad software (San Diego, California, United States). Continuous variables were expressed as means ± standard deviation and p < 0.05 was considered statistically significant.

Results From CP-OCT, a marked increase in surface reflectivity of dentin was observed after brushing with tested toothpastes. ESTP and NPsESTP showed higher or comparable grayscale values than Biorepair indicating increase in surface density of dentin. From SEM, at 2 weeks, ESTP showed comparable number of completely occluded dentinal tubules to Biorepair. TNPsESTP showed significantly lower numbers of CODT than Biorepair. At 1 month, the number of CODT was difficult to count for all treated groups. Both ESTP and TNPsESTP showed significantly higher numbers of partially occluded dentinal tubules than Biorepair.

Conclusion ESTP or TNPsESTP could offer a cost-effective substitute for the treatment of dentin hypersensitivity.

Dependency of hydration and growth conditions on the mechanical properties of oral biofilms

Within the oral cavity, dental biofilms experience dynamic environments, in part due to changes in dietary content, frequency of intake and health conditions. This can impact bacterial diversity and morpho-mechanical properties. While phenotypic properties of oral biofilms are closely related to their composition, these can readily change according to dynamic variations in the growth environment and nutrient availability. Understanding the interlink between phenotypic properties, variable growth conditions, and community characterization is an essential requirement to develop structure–property relationships in oral-biofilms. In this study, the impact of two distinct growth media types with increasing richness on the properties of oral biofilms was assessed through a new combination of in-vitro time-lapse biophysical methods with microbiological assays. Oral biofilms grown in the enriched media composition presented a decrease in their pH, an increase in soluble EPS production, and a severe reduction in bacterial diversity. Additionally, enriched media conditions presented an increase in biofilm volumetric changes (upon hydration) as well as a reduction in elastic modulus upon indentation. With hydration time considered a major factor contributing to changes in biofilm mechanical properties, we have shown that it is less associated than media richness. Future investigations can now use this time-lapse approach, with a clearer focus on the extracellular matrix of oral biofilms dictating their morpho-mechanical properties.

In Vitro Efficacy of Bacterial Cellulose Dressings Chemisorbed with Antiseptics against Biofilm Formed by Pathogens Isolated from Chronic Wounds

Local administration of antiseptics is required to prevent and fight against biofilm-based infections of chronic wounds. One of the methods used for delivering antiseptics to infected wounds is the application of dressings chemisorbed with antimicrobials. Dressings made of bacterial cellulose (BC) display several features, making them suitable for such a purpose. This work aimed to compare the activity of commonly used antiseptic molecules: octenidine, polyhexanide, povidone-iodine, chlorhexidine, ethacridine lactate, and hypochlorous solutions and to evaluate their usefulness as active substances of BC dressings against 48 bacterial strains (8 species) and 6 yeast strains (1 species). A silver dressing was applied as a control material of proven antimicrobial activity. The methodology applied included the assessment of minimal inhibitory concentrations (MIC) and minimal biofilm eradication concentration (MBEC), the modified disc-diffusion method, and the modified antibiofilm dressing activity measurement (A.D.A.M.) method. While in 96-well plate-based methods (MIC and MBEC assessment), the highest antimicrobial activity was recorded for chlorhexidine, in the modified disc-diffusion method and in the modified A.D.A.M test, povidone-iodine performed the best. In an in vitro setting simulating chronic wound conditions, BC dressings chemisorbed with polyhexanide, octenidine, or povidone-iodine displayed a similar or even higher antibiofilm activity than the control dressing containing silver molecules. If translated into clinical conditions, the obtained results suggest high applicability of BC dressings chemisorbed with antiseptics to eradicate biofilm from chronic wounds.

Advances in Optical Detection of Human-Associated Pathogenic Bacteria

Bacterial infection is a global burden that results in numerous hospital visits and deaths annually. The rise of multi-drug resistant bacteria has dramatically increased this burden. Therefore, there is a clinical need to detect and identify bacteria rapidly and accurately in their native state or a culture-free environment. Current diagnostic techniques lack speed and effectiveness in detecting bacteria that are culture-negative, as well as options for in vivo detection. The optical detection of bacteria offers the potential to overcome these obstacles by providing various platforms that can detect bacteria rapidly, with minimum sample preparation, and, in some cases, culture-free directly from patient fluids or even in vivo. These modalities include infrared, Raman, and fluorescence spectroscopy, along with optical coherence tomography, interference, polarization, and laser speckle. However, these techniques are not without their own set of limitations. This review summarizes the strengths and weaknesses of utilizing each of these optical tools for rapid bacteria detection and identification.

In-situ monitoring of the unstable bacterial adhesion process during wastewater biofilm formation: A comprehensive study

The initial bacterial adhesion phase is a pivotal and unstable step in the formation of biofilms. The initiation of biofilm formation is an unstable process caused by the reversible adhesion of bacteria, which is always time-consuming and yet to be elucidated. In this study, impedance-based real time cell analysis (RTCA) was employed to comprehensively investigate the initial bacterial adhesion process. Results showed that the time required for the unstable adhesion process was significantly (p < 0.05) reduced by increasing the initial concentration of bacteria, which is mainly attributed to the large deposition rate of bacteria at high concentrations. In addition, the unstable adhesion process is also regulated by shear stress, derived in this work from orbital shaking. Shear stress improves the reversibility of unstable bacterial attachment. Furthermore, attachment characteristics during the unstable phase vary between different species of bacteria (Sphingomonas rubra, Nakamurella multipartita and mixed bacteria). The S. rubra strain and mixed culture were more prone to adhere to the substratum surface during the unstable process, which was attributed to the smaller xDLVO energy barrier and motility of species in comparison with N. multipartita. Meanwhile, the molecular composition of extracellular polymeric substances (EPS) in the initial attachment phase presented a significant difference in expressed proteins, indicating the important role of proteins in EPS that strengthen bacterial adhesion. Overall, these findings suggest that during the biofilm reactor start-up process, seed sludge conditions, including the bacterial concentration, composition and hydraulics, need to be carefully considered.

An open-source robotic platform that enables automated monitoring of replicate biofilm cultivations using optical coherence tomography

The paper introduces a fully automated cultivation and monitoring tool to study biofilm development in replicate experiments operated in parallel. To gain a fundamental understanding of the relation between cultivation conditions and biofilm characteristics (e.g., structural, mechanical) a monitoring setup allowing for the standardization of methods is required. Optical coherence tomography (OCT) is an imaging modality ideal for biofilms since it allows for the monitoring of structure in real time. By integrating an OCT device into the open-source robotic platform EvoBot, a fully automated monitoring platform for investigating biofilm development in several flow cells at once was realized. Different positioning scenarios were tested and revealed that the positioning accuracy is within the optical resolution of the OCT. On that account, a reliable and accurate monitoring of biofilm development by means of OCT has become possible. With this robotic platform, reproducible biofilm experiments including a statistical analysis are achievable with only a small investment of operator time. Furthermore, a number of structural parameters calculated within this study confirmed the necessity to perform replicate biofilm cultivations.

Pilot-Scale Assessment of Urea as a Chemical Cleaning Agent for Biofouling Control in Spiral-Wound Reverse Osmosis Membrane Elements

Routine chemical cleaning with the combined use of sodium hydroxide (NaOH) and hydrochloric acid (HCl) is carried out as a means of biofouling control in reverse osmosis (RO) membranes. The novelty of the research presented herein is in the application of urea, instead of NaOH, as a chemical cleaning agent to full-scale spiral-wound RO membrane elements. A comparative study was carried out at a pilot-scale facility at the Evides Industriewater DECO water treatment plant in the Netherlands. Three fouled 8-inch diameter membrane modules were harvested from the lead position of one of the full-scale RO units treating membrane bioreactor (MBR) permeate. One membrane module was not cleaned and was assessed as the control. The second membrane module was cleaned by the standard alkali/acid cleaning protocol. The third membrane module was cleaned with concentrated urea solution followed by acid rinse. The results showed that urea cleaning is as effective as the conventional chemical cleaning with regards to restoring the normalized feed channel pressure drop, and more effective in terms of (i) improving membrane permeability, and (ii) solubilizing organic foulants and the subsequent removal of the surface fouling layer. Higher biomass removal by urea cleaning was also indicated by the fact that the total organic carbon (TOC) content in the HCl rinse solution post-urea-cleaning was an order of magnitude greater than in the HCl rinse after standard cleaning. Further optimization of urea-based membrane cleaning protocols and urea recovery and/or waste treatment methods is proposed for full-scale applications.

Chemical efficacy of several NaOCl concentrations on biofilms of different architecture: new insights on NaOCl working mechanisms

AIM

To investigate the anti-biofilm efficacy and working mechanism of several NaOCl concentrations on dual-species biofilms of different architecture as well as the changes induced on the architecture of the remaining biofilms.

METHODOLOGY

Streptococcus oralis J22 and Actinomyces naeslundii T14V-J1 were co-cultured under different growth conditions on saliva-coated hydroxyapatite discs. A constant-depth film fermenter (CDFF) was used to grow steady-state, four-day mature biofilms (dense architecture). Biofilms were grown under static conditions for 4 days within a confined space (less dense architecture). Twenty microlitres of buffer, 2-, 5-, and 10% NaOCl were applied statically on the biofilms for 60 s. Biofilm disruption and dissolution, as well as bubble formation, were evaluated with optical coherence tomography (OCT). The viscoelastic profile of the biofilms post-treatment was assessed with low load compression testing (LLCT). The bacteria/extracellular polysaccharide (EPS) content of the biofilms was examined through confocal laser scanning microscopy (CLSM). OCT, LLCT and CLSM data were analysed through one-way analysis of variance (ANOVA) and Tukey's HSD post-hoc test. Linear regression analysis was performed to test the correlation between bubble formation and NaOCl concentration. The level of significance was set at a < 0.05.

RESULTS

The experimental hypothesis according to which enhanced biofilm disruption, dissolution and bubble formation were anticipated with increasing NaOCl concentration was generally confirmed in both biofilm types. Distinct differences between the two biofilm types were noted with regard to NaOCl anti-biofilm efficiency as well as the effect that the several NaOCl concentrations had on the viscoelasticity profile and the bacteria/EPS content. Along with the bubble generation patterns observed, these led to the formulation of a concentration and biofilm structure-dependent theory of biofilm removal.

CONCLUSIONS

Biofilm architecture seems to be an additional determining factor of the penetration capacity of NaOCl, and consequently of its anti-biofilm efficiency.

Factors affecting the chemical efficacy of 2% sodium hypochlorite against oral steady-state dual-species biofilms: Exposure time and volume application

AIM

To study the influence of time and volume of 2% sodium hypochlorite (NaOCl) on biofilm removal and to investigate the changes induced on the biofilm architecture. Steady-state, dual-species biofilms of standardized thickness and a realistic contact surface area between biofilms and NaOCl were used.

METHODOLOGY

Streptococcus oralis J22 and Actinomyces naeslundii T14V-J1 biofilms were grown on saliva-coated hydroxyapatite discs within sample holders in the Constant Depth Film Fermenter (CDFF) for 96 h. Two per cent NaOCl was statically applied for three different time intervals (60, 120 and 300 s) and in two different volumes (20 and 40 μL) over the biofilm samples. The diffusion-driven effects of time and volume on biofilm disruption and dissolution were assessed with Optical Coherence Tomography (OCT). Structural changes of the biofilms treated with 2% NaOCl were studied with Confocal Laser Scanning Microscopy (CLSM) and Low Load Compression Testing (LLCT). A two-way analysis of variance (2-way anova) was performed, enabling the effect of each independent variable as well as their interaction on the outcome measures.

RESULTS

Optical coherence tomography revealed that by increasing the exposure time and volume of 2% NaOCl, both biofilm disruption and dissolution significantly increased. Analysis of the interaction between the two independent variables revealed that by increasing the volume of 2% NaOCl, significant biofilm dissolution could be achieved in less time. Examination of the architecture of the remaining biofilms corroborated the EPS-lytic action of 2% NaOCl, especially when greater volumes were applied. The viscoelastic analysis of the 2% NaOCl-treated biofilms revealed that the preceding application of higher volumes could impact their subsequent removal.

CONCLUSIONS

Time and volume of 2% NaOCl application should be taken into account for maximizing the anti-biofilm efficiency of the irrigant and devising targeted disinfecting regimes against remaining biofilms.

Bacterial Density and Biofilm Structure Determined by Optical Coherence Tomography

Optical-coherence-tomography (OCT) is a non-destructive tool for biofilm imaging, not requiring staining, and used to measure biofilm thickness and putative comparison of biofilm structure based on signal intensity distributions in OCT-images. Quantitative comparison of biofilm signal intensities in OCT-images, is difficult due to the auto-scaling applied in OCT-instruments to ensure optimal quality of individual images. Here, we developed a method to eliminate the influence of auto-scaling in order to allow quantitative comparison of biofilm densities in different images. Auto- and re-scaled signal intensities could be qualitatively interpreted in line with biofilm characteristics for single and multi-species biofilms of different strains and species (cocci and rod-shaped organisms), demonstrating qualitative validity of auto- and re-scaling analyses. However, specific features of pseudomonas and oral multi-species biofilms were more prominently expressed after re-scaling. Quantitative validation was obtained by relating average auto- and re-scaled signal intensities across biofilm images with volumetric-bacterial-densities in biofilms, independently obtained using enumeration of bacterial numbers per unit biofilm volume. The signal intensities in auto-scaled biofilm images did not significantly relate with volumetric-bacterial-densities, whereas re-scaled intensities in images of biofilms of widely different strains and species increased linearly with independently determined volumetric-bacterial-densities in the biofilms. Herewith, the proposed re-scaling of signal intensity distributions in OCT-images significantly enhances the possibilities of biofilm imaging using OCT.

Optical coherence tomography imaging of cardiac substrates

Cardiovascular disease is the leading cause of morbidity and mortality in the United States. Knowledge of a patient's heart structure will help to plan procedures, potentially identifying arrhythmia substrates, critical structures to avoid, detect transplant rejection, and reduce ambiguity when interpreting electrograms and functional measurements. Similarly, basic research of numerous cardiac diseases would greatly benefit from structural imaging at cellular scale. For both applications imaging on the scale of a myocyte is needed, which is approximately 100 µm × 10 µm. The use of optical coherence tomography (OCT) as a tool for characterizing cardiac tissue structure and function has been growing in the past two decades. We briefly review OCT principles and highlight important considerations when imaging cardiac muscle. In particular, image penetration, tissue birefringence, and light absorption by blood during in vivo imaging are important factors when imaging the heart with OCT. Within the article, we highlight applications of cardiac OCT imaging including imaging heart tissue structure in small animal models, quantification of myofiber organization, monitoring of radiofrequency ablation (RFA) lesion formation, structure-function analysis enabled by functional extensions of OCT and multimodal analysis and characterizing important substrates within the human heart. The review concludes with a summary and future outlook of OCT imaging the heart, which is promising with progress in optical catheter development, functional extensions of OCT, and real time image processing to enable dynamic imaging and real time tracking during therapeutic procedures.

Enhanced biofilm solubilization by urea in reverse osmosis membrane systems

Chemical cleaning is routinely performed in reverse osmosis (RO) plants for the regeneration of RO membranes that suffer from biofouling problems. The potential of urea as a chaotropic agent to enhance the solubilization of biofilm proteins has been reported briefly in the literature. In this paper the efficiency of urea cleaning for RO membrane systems has been compared to conventionally applied acid/alkali treatment. Preliminary assessment confirmed that urea did not damage the RO polyamide membranes and that the membrane cleaning efficiency increased with increasing concentrations of urea and temperature. Accelerated biofilm formation was carried out in membrane fouling simulators which were subsequently cleaned with (i) 0.01M sodium hydroxide (NaOH) and 0.1M hydrochloric acid (HCl) (typically applied in industry), (ii) urea (CO(NH2)2) and hydrochloric acid, or (iii) urea only (1340 g/Lwater). The pressure drop over the flow channel was used to evaluate the efficiency of the applied chemical cleanings. Biomass removal was evaluated by measuring chemical oxygen demand (COD), adenosine triphosphate (ATP), protein, and carbohydrate content from the membrane and spacer surfaces after cleaning. In addition to protein and carbohydrate quantification of the extracellular polymeric substances (EPS), fluorescence excitation-emission matrix (FEEM) spectroscopy was used to distinguish the difference in organic matter of the remaining biomass to assess biofilm solubilization efficacy of the different cleaning agents. Results indicated that two-stage CO(NH2)2/HCl cleaning was as effective as cleaning with NaOH/HCl in terms of restoring the feed channel pressure drop (>70% pressure drop decrease). One-stage cleaning with urea only was not as effective indicating the importance of the second-stage low pH acid cleaning in weakening the biofilm matrix. All three chemical cleaning protocols were equally effective in reducing the concentration of predominant EPS components protein and carbohydrate (>50% reduction in concentrations). However, urea-based cleaning strategies were more effective in solubilizing protein-like matter and tyrosine-containing proteins. Furthermore, ATP measurements showed that biomass inactivation was up to two-fold greater after treatment with urea-based chemical cleanings compared to the conventional acid/alkali treatment. The applicability of urea as an alternative, economical, eco-friendly and effective chemical cleaning agent for the control of biological fouling was successfully demonstrated.

Options and Limitations in Clinical Investigation of Bacterial Biofilms

Bacteria can form single- and multispecies biofilms exhibiting diverse features based upon the microbial composition of their community and microenvironment. The study of bacterial biofilm development has received great interest in the past 20 years and is motivated by the elegant complexity characteristic of these multicellular communities and their role in infectious diseases. Biofilms can thrive on virtually any surface and can be beneficial or detrimental based upon the community's interplay and the surface. Advances in the understanding of structural and functional variations and the roles that biofilms play in disease and host-pathogen interactions have been addressed through comprehensive literature searches. In this review article, a synopsis of the methodological landscape of biofilm analysis is provided, including an evaluation of the current trends in methodological research. We deem this worthwhile because a keyword-oriented bibliographical search reveals that less than 5% of the biofilm literature is devoted to methodology. In this report, we (i) summarize current methodologies for biofilm characterization, monitoring, and quantification; (ii) discuss advances in the discovery of effective imaging and sensing tools and modalities; (iii) provide an overview of tailored animal models that assess features of biofilm infections; and (iv) make recommendations defining the most appropriate methodological tools for clinical settings.

Novel evaluation and treatment techniques for white spot lesions. An in vitro study

OBJECTIVE

White spot lesions (WSLs) are commonly seen during and after orthodontic treatment. Therefore, the objective of this in vitro study was to assess the effect of 45S5-bioglass in remineralizing WSLs using cross-polarization optical coherence tomography (CP-OCT) and confirm the findings by micro-hardness test.

METHODS

Ceramic orthodontic brackets were bonded to the buccal surface of 45 human premolars with Transbond XT primer followed by Transbond PLUS according to the manufacturer's instructions. Then, all specimens were varnished excluding the area of interest (AOI) around the bonded brackets, immersed in demineralizing solution and divided into three groups: BG, REM and CONT. In BG group, 15 specimens were treated with bioglass paste for 24 hours. REM group had 15 specimens stored in remineralization solution for 24 hours. CONT group had the remaining 15 specimens with no treatment. All specimens were examined under CP-OCT and tested using cross-sectional micro-hardness techniques.

RESULTS

CP-OCT analysis showed that the maximum pixel value after bioglass application was significantly increased at AOI when compared to CONT and REM groups (P>.05), which was confirmed by the cross-sectional micro-hardness results (P>.05).

CONCLUSION

Early enamel demineralization and remineralization can be easily and non-invasively monitored with CP-OCT. Bioglass is a potent remineralizing agent.

A Multi-scale Biophysical Approach to Develop Structure-Property Relationships in Oral Biofilms

Over the last 5–10 years, optical coherence tomography (OCT) and atomic force microscopy (AFM) have been individually applied to monitor the morphological and mechanical properties of various single-species biofilms respectively. This investigation looked to combine OCT and AFM as a multi-scale approach to understand the role sucrose concentration and age play in the morphological and mechanical properties of oral, microcosm biofilms, in-vitro. Biofilms with low (0.1% w/v) and high (5% w/v) sucrose concentrations were grown on hydroxyapatite (HAP) discs from pooled human saliva and incubated for 3 and 5 days. Distinct mesoscale features of biofilms such as regions of low and high extracellular polymeric substances (EPS) were identified through observations made by OCT. Mechanical analysis revealed increasing sucrose concentration decreased Young’s modulus and increased cantilever adhesion (p < 0.0001), relative to the biofilm. Increasing age was found to decrease adhesion only (p < 0.0001). This was due to mechanical interactions between the indenter and the biofilm increasing as a function of increased EPS content, due to increasing sucrose. An expected decrease in EPS cantilever contact decreased adhesion due to bacteria proliferation with biofilm age. The application OCT and AFM revealed new structure-property relationships in oral biofilms, unattainable if the techniques were used independently.

Multicontrast endomyocardial imaging by single-channel high-resolution cross-polarization optical coherence tomography

A single-channel high-resolution cross-polarization (CP) optical coherence tomography (OCT) system is presented for multicontrast imaging of human myocardium in one-shot measurement. The intensity and functional contrasts, including the ratio between the cross- and co-polarization channels as well as the cumulative retardation, are reconstructed from the CP-OCT readout. By comparing the CP-OCT results with histological analysis, it is shown that the system can successfully delineate microstructures in the myocardium and differentiate the fibrotic myocardium from normal or ablated myocardium based on the functional contrasts provided by the CP-OCT system. The feasibility of using A-line profiles from the 2 orthogonal polarization channels to identify fibrotic myocardium, normal myocardium and ablated lesion is also discussed.

Chlorhexidine-induced elastic and adhesive changes of Escherichia coli cells within a biofilm

Chlorhexidine is a widely used, commercially available cationic antiseptic. Although its mechanism of action on planktonic bacteria has been well explored, far fewer studies have examined its interaction with an established biofilm. The physical effects of chlorhexidine on a biofilm are particularly unknown. Here, the authors report the first observations of chlorhexidine-induced elastic and adhesive changes to single cells within a biofilm. The elastic changes are consistent with the proposed mechanism of action of chlorhexidine. Atomic force microscopy and force spectroscopy techniques were used to determine spring constants and adhesion energy of the individual bacteria within an Escherichia coli biofilm. Medically relevant concentrations of chlorhexidine were tested, and cells exposed to 1% (w/v) and 0.1% more than doubled in stiffness, while those exposed to 0.01% showed no change in elasticity. Adhesion to the biofilm also increased with exposure to 1% chlorhexidine, but not for the lower concentrations tested. Given the prevalence of chlorhexidine in clinical and commercial applications, these results have important ramifications on biofilm removal techniques.

Measurement of biofilm growth and local hydrodynamics using optical coherence tomography

We report on localized and simultaneous measurement of biofilm growth and local hydrodynamics in a microfluidic channel using optical coherence tomography. We measure independently with high spatio-temporal resolution the longitudinal flow velocity component parallel to the imaging beam and the transverse flow velocity component perpendicular to the imaging beam. Based on the measured velocities we calculate the shear-rates in the flow channel. We show the relation between the measured biofilm structure and flow velocities as biofilm growth progresses over the course of 48 hours.