An Integrated Microsystem for Real-Time Detection and Threshold-Activated Treatment of Bacterial Biofilms

A Review of Recent Advancements in Sensor-Integrated Medical Tools

A medical tool is a general instrument intended for use in the prevention, diagnosis, and treatment of diseases in humans or other animals. Nowadays, sensors are widely employed in medical tools to analyze or quantify disease-related parameters for the diagnosis and monitoring of patients' diseases. Recent explosive advancements in sensor technologies have extended the integration and application of sensors in medical tools by providing more versatile in vivo sensing capabilities. These unique sensing capabilities, especially for medical tools for surgery or medical treatment, are getting more attention owing to the rapid growth of minimally invasive surgery. In this review, recent advancements in sensor-integrated medical tools are presented, and their necessity, use, and examples are comprehensively introduced. Specifically, medical tools often utilized for medical surgery or treatment, for example, medical needles, catheters, robotic surgery, sutures, endoscopes, and tubes, are covered, and in-depth discussions about the working mechanism used for each sensor-integrated medical tool are provided.

Sensor system for analysis of biofilm sensitivity to ampicillin

The resistance of biofilms to antibiotics is a key factor that makes bacterial infections unsusceptible to antimicrobial therapy. The results of classical tests of cell sensitivity to antibiotics cannot be used to predict therapeutic success in infections associated with biofilm formation. We describe a simple and rapid method for the real-time evaluation of bacterial biofilm sensitivity to antibiotics, with Pseudomonas putida and ampicillin as examples. The method uses an electric biosensor to detect the difference between changes in the biofilm electric polarizability, thereby evaluating antibiotic sensitivity. The electric signals showed that P. putida biofilms were susceptible to ampicillin and that at high antibiotic concentrations, the biofilms differed markedly in their susceptibility (dose-dependent effect). The sensor also detected differences between biofilms before and after ampicillin treatment. The electric-signal changes enabled us to describe the physical picture of the processes occurring in bacterial biofilms in the presence of ampicillin. The approach used in this study is promising for evaluating the activity of various compounds against biofilms, because it permits a conclusion about the antibiotic sensitivity of biofilm bacteria to be made in real time and in a short period (analysis time, not longer than 20 min). An added strong point is that analysis can be done directly in liquid, without preliminary sample preparation. KEY POINTS: • Sensor system to analyze biofilm antimicrobial susceptibility is described. • The signal change depended on the ampicillin concentration (dose-dependent effect). • The sensor allows real-time determination of the antibiofilm effect of ampicillin.

Guided mode resonance immunosensor for label-free detection of pathogenic bacteria Pseudomonas aeruginosa

Photonic biosensors are promising platforms for the rapid detection of pathogens with the potential to replace conventional diagnostics based on microbiological culturing methods. Intricately designed sensing elements with robust architectures can offer highly sensitive detection at minimal development cost enabling rapid adoption in low-resource settings. In this work, an optical detection scheme is developed by structuring guided mode resonance (GMR) on a highly stable, transparent silicon nitride (SiN) substrate and further biofunctionalized to identify a specific bacteria Pseudomonas aeruginosa. The resonance condition of the GMR chip is optimized to have relatively high bulk sensitivity with a good quality factor. The biofunctionalization aims at oriented immobilization of specific antibodies to allow maximum bacteria attachment and improved specificity. The sensitivity of the assays is evaluated for clinically relevant concentrations ranging from 102 to 108 CFU/mL. From the calibration curves, the sensitivity of the chip is extracted as 0.134nm/Log10 [concentration], and the detection modality possesses a favorably good limit of detection (LOD) 89 CFU/mL. The use of antibodies as a biorecognition element complemented with a good figure of merit of GMR sensing element allows selective bacteria identification compared to other non-specific pathogenic bacteria that are relevant for testing physiological samples. Our developed GMR biosensor is low-cost, easy to handle, and readily transformable into a portable handheld detection modality for remote usage.

Electrochemical Impedance Spectroscopy-Based Sensing of Biofilms: A Comprehensive Review

Biofilms are complex communities of microorganisms that can form on various surfaces, including medical devices, industrial equipment, and natural environments. The presence of biofilms can lead to a range of problems, including infections, reduced efficiency and failure of equipment, biofouling or spoilage, and environmental damage. As a result, there is a growing need for tools to measure and monitor levels of biofilms in various biomedical, pharmaceutical, and food processing settings. In recent years, electrochemical impedance sensing has emerged as a promising approach for real-time, non-destructive, and rapid monitoring of biofilms. This article sheds light on electrochemical sensing for measuring biofilms, including its high sensitivity, non-destructive nature, versatility, low cost, and real-time monitoring capabilities. We also discussed some electrochemical sensing applications for studying biofilms in medical, environmental, and industrial settings. This article also presents future perspectives for research that would lead to the creation of reliable, quick, easy-to-use biosensors mounted on unmanned aerial vehicles (UAVs), and unmanned ground vehicles (UGVs), utilizing artificial intelligence-based terminologies to detect biofilms.

A Novel Hybrid Platform for Live/Dead Bacteria Accurate Sorting by On-Chip DEP Device

According to the World Health Organization (WHO) forecasts, Antimicrobial Resistance (AMR) will be the leading cause of death worldwide in the next decades. To prevent this phenomenon, rapid Antimicrobial Susceptibility Testing (AST) techniques are required to drive the selection of the most suitable antibiotic and its dosage. In this context, we propose an on-chip platform, based on a micromixer and a microfluidic channel, combined with a pattern of engineered electrodes to exploit the di-electrophoresis (DEP) effect. The role of the micromixer is to ensure the proper interaction of the antibiotic with the bacteria over a long time (≈1 h), and the DEP-based microfluidic channel enables the efficient sorting of live from dead bacteria. A sorting efficiency of more than 98%, with low power consumption (V_pp = 1 V) and time response of 5 s, within a chip footprint of ≈86 mm², has been calculated, which makes the proposed system very attractive and innovative for efficient and rapid monitoring of the antimicrobial susceptibility at the single-bacterium level in next-generation medicine.

Monitoring biofilm growth and dispersal in real-time with impedance biosensors

Microbial biofilm contamination is a widespread problem that requires precise and prompt detection techniques to effectively control its growth. Microfabricated electrochemical impedance spectroscopy (EIS) biosensors offer promise as a tool for early biofilm detection and monitoring of elimination. This study utilized a custom flow cell system with integrated sensors to make real-time impedance measurements of biofilm growth under flow conditions, which were correlated with confocal laser scanning microscopy (CLSM) imaging. Biofilm growth on EIS biosensors in basic aqueous growth media (tryptic soy broth, TSB) and an oil-water emulsion (metalworking fluid, MWF) attenuated in a sigmoidal decay pattern, which lead to an ∼22-25% decrease in impedance after 24 Hrs. Subsequent treatment of established biofilms increased the impedance by ∼14% and ∼41% in TSB and MWF, respectively. In the presence of furanone C-30, a quorum-sensing inhibitor (QSI), impedance remained unchanged from the initial time point for 18 Hrs in TSB and 72 Hrs in MWF. Biofilm changes enumerated from CLSM imaging corroborated impedance measurements, with treatment significantly reducing biofilm. Overall, these results support the application of microfabricated EIS biosensors for evaluating the growth and dispersal of biofilm in situ and demonstrate potential for use in industrial settings.

ONE-SENTENCE SUMMARY

This study demonstrates the use of microfabricated electrochemical impedance spectroscopy (EIS) biosensors for real-time monitoring and treatment evaluation of biofilm growth, offering valuable insights for biofilm control in industrial settings.

Review of Label-Free Monitoring of Bacteria: From Challenging Practical Applications to Basic Research Perspectives

Novel biosensors already provide a fast way to detect the adhesion of whole bacteria (or parts of them), biofilm formation, and the effect of antibiotics. Moreover, the detection sensitivities of recent sensor technologies are large enough to investigate molecular-scale biological processes. Usually, these measurements can be performed in real time without using labeling. Despite these excellent capabilities summarized in the present work, the application of novel, label-free sensor technologies in basic biological research is still rare; the literature is dominated by heuristic work, mostly monitoring the presence and amount of a given analyte. The aims of this review are (i) to give an overview of the present status of label-free biosensors in bacteria monitoring, and (ii) to summarize potential novel directions with biological relevancies to initiate future development. Optical, mechanical, and electrical sensing technologies are all discussed with their detailed capabilities in bacteria monitoring. In order to review potential future applications of the outlined techniques in bacteria research, we summarize the most important kinetic processes relevant to the adhesion and survival of bacterial cells. These processes are potential targets of kinetic investigations employing modern label-free technologies in order to reveal new fundamental aspects. Resistance to antibacterials and to other antimicrobial agents, the most important biological mechanisms in bacterial adhesion and strategies to control adhesion, as well as bacteria-mammalian host cell interactions are all discussed with key relevancies to the future development and applications of biosensors.

In situ continuous electrochemical quantification of bacterial adhesion to electrically polarized metallic surfaces under shear

Biofouling creates significant human and economic losses through infections, corrosion, and drag losses on ships and in oil and food distribution pipelines. Organisms adhered to these surfaces contend with high shear rates and are actively transported to the surface. The metallic surfaces to which these organisms are adhered also conduct charge at various potentials, and the effects of surface charge on adhesion rates are little addressed in the literature. We demonstrate that mass-transport limiting current, chronoamperometry, and cyclic voltammetry can be combined to provide resulting adhesion rates similar to those in the literature. Furthermore, we demonstrate that rotating disk electrodes can be used to study adhesion of bacteria to electrically polarized metallic surfaces under shear. We study the adhesion of Escherichia coli, Bacillus subtilis, and 1μm silica microspheres over a range of shear stress from 0.15 to 37  dyncm^-2 or shear rates of 14.7-3730  s^-1. Unlike quartz-crystal microbalance, our methodology measures changes in the area instead of mass, simultaneously providing measurements of the protein binding. Our deposition rates agree with those found using optical systems. However, unlike optical systems, our methods apply to a wider range of materials than on-chip flow devices.

Detection and Characterization of Bacterial Biofilms and Biofilm-Based Sensors

Microbial biofilms have caused serious concerns in healthcare, medical, and food industries because of their intrinsic resistance against conventional antibiotics and cleaning procedures and their capability to firmly adhere on surfaces for persistent contamination. These global issues strongly motivate researchers to develop novel methodologies to investigate the kinetics underlying biofilm formation, to understand the response of the biofilm with different chemical and physical treatments, and to identify biofilm-specific drugs with high-throughput screenings. Meanwhile microbial biofilms can also be utilized positively as sensing elements in cell-based sensors due to their strong adhesion on surfaces. In this perspective, we provide an overview on the connections between sensing and microbial biofilms, focusing on tools used to investigate biofilm properties, kinetics, and their response to chemicals or physical agents, and biofilm-based sensors, a type of biosensor using the bacterial biofilm as a biorecognition element to capture the presence of the target of interest by measuring the metabolic activity of the immobilized microbial cells. Finally we discuss possible new research directions for the development of robust and rapid biofilm related sensors with high temporal and spatial resolutions, pertinent to a wide range of applications.

Novel Micro-Nano Optoelectronic Biosensor for Label-Free Real-Time Biofilm Monitoring

According to the World Health Organization forecasts, AntiMicrobial Resistance (AMR) is expected to become one of the leading causes of death worldwide in the following decades. The rising danger of AMR is caused by the overuse of antibiotics, which are becoming ineffective against many pathogens, particularly in the presence of bacterial biofilms. In this context, non-destructive label-free techniques for the real-time study of the biofilm generation and maturation, together with the analysis of the efficiency of antibiotics, are in high demand. Here, we propose the design of a novel optoelectronic device based on a dual array of interdigitated micro- and nanoelectrodes in parallel, aiming at monitoring the bacterial biofilm evolution by using optical and electrical measurements. The optical response given by the nanostructure, based on the Guided Mode Resonance effect with a Q-factor of about 400 and normalized resonance amplitude of about 0.8, allows high spatial resolution for the analysis of the interaction between planktonic bacteria distributed in small colonies and their role in the biofilm generation, calculating a resonance wavelength shift variation of 0.9 nm in the presence of bacteria on the surface, while the electrical response with both micro- and nanoelectrodes is necessary for the study of the metabolic state of the bacteria to reveal the efficacy of antibiotics for the destruction of the biofilm, measuring a current change of 330 nA when a 15 µm thick biofilm is destroyed with respect to the absence of biofilm.

Integrated System for Bacterial Detection and Biofilm Treatment On Indwelling Urinary Catheters

GOAL

This work introduces an integrated system incorporated seamlessly with a commercial Foley urinary catheter for bacterial growth sensing and biofilm treatment.

METHODS

The system is comprised of flexible, interdigitated electrodes incorporated with a urinary catheter via a 3D-printed insert for impedance sensing and bioelectric effect-based treatment. Each of the functions were wirelessly controlled using a custom application that provides a user-friendly interface for communicating with a custom PCB via Bluetooth to facilitate implementation in practice.

RESULTS

The integrated catheter system maintains the primary functions of indwelling catheters - urine drainage, balloon inflation - while being capable of detecting the growth of Escherichia coli, with an average decrease in impedance of 13.0% after 24 hours, tested in a newly-developed simulated bladder environment. Furthermore, the system enables bioelectric effect-based biofilm reduction, which is performed by applying a low-intensity electric field that increases the susceptibility of biofilm bacteria to antimicrobials, ultimately reducing the required antibiotic dosage.

CONCLUSION

Overall, this modified catheter system represents a significant step forward for catheter-associated urinary tract infection (CAUTI) management using device-based approaches, integrating flexible electrodes with an actual Foley catheter along with the control electronics and mobile application.

SIGNIFICANCE

CAUTIs, exacerbated by the emergence of antibiotic-resistant pathogens, represent a significant challenge as one of the most prevalent healthcare-acquired infections. These infections are driven by the colonization of indwelling catheters by bacterial biofilms.

Microsystems for biofilm characterization and sensing - A review

Biofilms are the primary cause of clinical bacterial infections and are impervious to typical amounts of antibiotics, necessitating very high doses for elimination. Therefore, it is imperative to have suitable methods for characterization to develop novel methods of treatment that can complement or replace existing approaches using significantly lower doses of antibiotics. This review presents some of the current developments in microsystems for characterization and sensing of bacterial biofilms. Initially, we review current standards for studying biofilms that are based on invasive and destructive end-point biofilm characterization. Additionally, biofilm formation and growth is extremely sensitive to various growth and environmental parameters that cause large variability in biofilms between repeated experiments, making it very difficult to compare experimental repeats and characterize the temporal characteristics of these organisms. To address these challenges, recent developments in the field have moved toward systems and miniature devices that can aid in the non-invasive characterization of bacterial biofilms. Our review focuses on several types of microsystems for biofilm evaluation including optical, electrochemical, and mechanical systems. This review will show how these devices can lead to better understanding of the physiology and function of these communities of bacteria, which can eventually lead to the development of novel treatments that do not rely on high-dosage antibiotics.

3D-Printed electrochemical sensor-integrated transwell systems

This work presents a 3D-printed, modular, electrochemical sensor-integrated transwell system for monitoring cellular and molecular events in situ without sample extraction or microfluidics-assisted downstream omics. Simple additive manufacturing techniques such as 3D printing, shadow masking, and molding are used to fabricate this modular system, which is autoclavable, biocompatible, and designed to operate following standard operating protocols (SOPs) of cellular biology. Integral to the platform is a flexible porous membrane, which is used as a cell culture substrate similarly to a commercial transwell insert. Multimodal electrochemical sensors fabricated on the membrane allow direct access to cells and their products. A pair of gold electrodes on the top side of the membrane measures impedance over the course of cell attachment and growth, characterized by an exponential decrease (~160% at 10 Hz) due to an increase in the double layer capacitance from secreted extracellular matrix (ECM) proteins. Cyclic voltammetry (CV) sensor electrodes, fabricated on the bottom side of the membrane, enable sensing of molecular release at the site of cell culture without the need for downstream fluidics. Real-time detection of ferrocene dimethanol injection across the membrane showed a three order-of-magnitude higher signal at the membrane than in the bulk media after reaching equilibrium. This modular sensor-integrated transwell system allows unprecedented direct, real-time, and noninvasive access to physical and biochemical information, which cannot be obtained in a conventional transwell system.

Study of Real-Time Spatial and Temporal Behavior of Bacterial Biofilms Using 2-D Impedance Spectroscopy

OBJECTIVE

The purpose of this paper is to demonstrate the use of 2-D impedance spectroscopy to identify areas of biofilm growth on a CMOS biosensor microelectrode-array.

METHODS

This paper presents the design and use of a novel multichannel impedance spectroscopy instrument to allow 2-D spatial and temporal evaluation of biofilm growth. The custom-designed circuits can provide a wide range of frequencies (1 Hz-100 kHz) to allow customization of impedance measurements, as the frequency of interest varies based on the type and state of biofilm under measurement. The device is capable of taking measurements as fast as once per second on the entire set of impedance sensors, allowing real-time observation. It also supports adjustable stimulus voltages. The distance between neighboring sensors is 220 micrometers which provides reasonable spatial resolution for biofilm study.

RESULTS

Biofilm was grown on the surface of the chip, occupancy was measured using the new tool, and the results were validated optically using fluorescent staining. The results show that the developed tool can be used to determine the bacterial biofilm presence at a given location.

CONCLUSION

This paper confirms that 2-D impedance spectroscopy can be used to measure biofilm occupancy. The new tool developed to perform the measurements was able to display real-time results, and determine biofilm coverage of the array electrodes.

SIGNIFICANCE

The system presented in this report is the first fully integrated 2-D EIS measurement system with full software support for capturing biofilm growth dynamics in real-time. Due to its ability to nondestructively monitor biofilms over time, 2-D impedance spectroscopy using a microelectrode-array is a useful tool for studying biofilms.

3D-Printed Microfluidic Devices for Enhanced Online Sampling and Direct Optical Measurements

3D printing has emerged as a robust technique to fabricate reliable and reproducible microfluidic devices. However, a limitation of 3D-printed devices has been the low transparency even when printed in a "clear" material. There are currently no reports regarding direct optical measurements through a 3D-printed device. Here, we present for the first time that the printing orientation can affect the transparency of a 3D-printed object. With the optimal orientation, we printed a microfluidic detector that was sufficiently transparent (transmittance ≈ 80%) for optical quantitation. This finding is significant because it shows the feasibility to directly 3D-print optical components for analytical applications. In addition, we created a novel microfluidic dialysis device via 3D printing, which enabled higher flow rates (for sampling with high temporal resolution) and increased extraction efficiency than commercially available ones. By coupling the microfluidic detector and dialysis probe, we successfully measured the release kinetics of indole from biofilms in a continuous, automated, and near real-time fashion. Indole is an intercellular signaling molecule in biofilms, which may regulate antibiotic resistance. The release kinetics of this molecule had not been quantitated likely because of the lack of a suitable analytical tool. Our results fill this knowledge gap.

Innovations in indwelling urethral catheterisation

The indwelling urethral catheter remains an integral part of contemporary medical care, despite its significant design shortcomings. Urethral catheterisation is responsible for well-recognised complications including catheter-associated urinary tract infection (CAUTI), catheter-associated urethral injury (CAUI), catheter blockage, and bladder mucosal irritation. In this narrative review, we provide an update on current innovations in urethral catheter design, aimed at safeguarding against these complications. There is an obvious need to improve catheter technology and urologists should support the translation of innovations into clinical practice.

Sensing the unreachable: challenges and opportunities in biofilm detection

Bacteria can attach to essentially all materials and form multicellular biofilms with high-level tolerance to antimicrobials. Detrimental biofilms are responsible for a variety of problems ranging from food and water contamination, bio-corrosion, to drug resistant infections. Besides the challenges in control, biofilms are also difficult to detect due to the lack of biofilm-specific biomarkers and methods for non-destructive imaging. In this article, we present a concise review of recent advancements in this field, with a focus on medical device-associated infections. We also discuss the technologies that have potential for non-destructive detection of bacterial biofilms.

Impedimetric transducers based on interdigitated electrode arrays for bacterial detection - A review

Application of the impedance spectroscopy technique to detection of bacteria has advanced considerably over the last decade. This is reflected by the large amount of publications focused on basic research and applications of impedance biosensors. Employment of modern technologies to significantly reduce dimension of impedimetric devices enable on-chip integration of interdigitated electrode arrays for low-cost and easy-to-use sensors. This review is focused on publications dealing with interdigitated electrodes as a transducer unit and different bacteria detection systems using these devices. The first part of the review deals with the impedance technique principles, paying special attention to the use of interdigitated electrodes, while the main part of this work is focused on applications ranging from bacterial growth monitoring to label-free specific bacteria detection.

Depriving Bacterial Adhesion-Related Molecule to Inhibit Biofilm Formation Using CeO2 -Decorated Metal-Organic Frameworks

The formation of bacterial biofilm is one of the causes of antimicrobial resistance, often leading to persistent infections and a high fatality rate. Therefore, there is an urgent need to develop novel and effective strategies to inhibit biofilm formation. Adenosine triphosphate (ATP) plays an important role in bacterial adhesion and biofilm formation through stimulating cell lysis and extracellular DNA (eDNA) release. Herein, a simple and robust strategy for inhibiting biofilm formation is developed using CeO₂ -decorated porphyrin-based metal-organic frameworks (MOFs). The function of extracellular ATP (eATP) can be inhibited by CeO₂ nanoparticles, leading to the disruption of the initial adhesion of bacteria. Furthermore, planktonic bacteria can be killed by cytotoxic reactive oxygen species (ROS) generated by MOFs. As a consequence, the synergic effect of eATP deprivation and ROS generation presents excellent capacity to prevent biofilm formation, which may provide a new direction for designing flexible and effective biofilm-inhibiting systems.

Recent Advances in the Race to Design a Rapid Diagnostic Test for Antimicrobial Resistance

Even with advances in antibiotic therapies, bacterial infections persistently plague society and have amounted to one of the most prevalent issues in healthcare today. Moreover, the improper and excessive administration of antibiotics has led to resistance of many pathogens to prescribed therapies, rendering such antibiotics ineffective against infections. While the identification and detection of bacteria in a patient's sample is critical for point-of-care diagnostics and in a clinical setting, the consequent determination of the correct antibiotic for a patient-tailored therapy is equally crucial. As a result, many recent research efforts have been focused on the development of sensors and systems that correctly guide a physician to the best antibiotic to prescribe for an infection, which can in turn, significantly reduce the instances of antibiotic resistance and the evolution of bacteria "superbugs." This review details the advantages and shortcomings of the recent advances (focusing from 2016 and onward) made in the developments of antimicrobial susceptibility testing (AST) measurements. Detection of antibiotic resistance by genomic AST techniques relies on the prediction of antibiotic resistance via extracted bacterial DNA content, while phenotypic determinations typically track physiological changes in cells and/or populations exposed to antibiotics. Regardless of the method used for AST, factors such as cost, scalability, and assay time need to be weighed into their design. With all of the expansive innovation in the field, which technology and sensing systems demonstrate the potential to detect antimicrobial resistance in a clinical setting?

Flexible Platform for In Situ Impedimetric Detection and Bioelectric Effect Treatment of Escherichia Coli Biofilms

GOAL

This paper reports a platform for real-time monitoring and treatment of biofilm formation on three-dimensional biomedical device surfaces.

METHODS

We utilize a flexible platform consisting of gold interdigitated electrodes patterned on a polyimide substrate. The device was integrated onto the interior of a urinary catheter and characterization was performed in a custom-developed flow system. Biofilm growth was monitored via impedance change at 100 Hz ac with a 50 mV signal amplitude.

RESULTS

A 30% impedance decrease over 24 h corresponded to Escherichia coli biofilm formation. The platform also enabled removal of the biofilm through the bioelectric effect; a low concentration of antibiotic combined with the applied ac voltage signal led to a synergistic reduction in biofilm resulting in a 12% increase in impedance. Biomass characterization via crystal violet staining confirmed that the impedance detection results correlate with changes in the amount of biofilm biomass on the sensor. We also demonstrated integration with a chip-based impedance converter to enable miniaturization and allow in situ wireless implementation. A 5% impedance decrease measured with the impedance converter corresponded to biofilm growth, replicating the trend measured with the potentiostat.

CONCLUSION

This platform represents a promising solution for biofilm infection management in diverse vulnerable environments.

SIGNIFICANCE

Biofilms are the dominant mode of growth for microorganisms, where bacterial cells colonize hydrated surfaces and lead to recurring infections. Due to the inaccessible nature of the environments where biofilms grow and their increased tolerance of antimicrobials, identification, and removal on medical devices poses a challenge.

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.

Weak electricigens: A new avenue for bioelectrochemical research

Electroactivity appears to be a phylogenetically diverse trait independent of cell wall classification, with both Gram-negative and Gram-positive electricigens reported. While numerous electricigens have been observed, the majority of research focuses on a select group of highly electroactive species. Under favorable conditions, many microorganisms can be considered electroactive, either through their own mechanisms or exogenously-added mediators, producing a weak current. Such microbes should not be dismissed based on their modest electroactivity. Rather, they may be key to understanding what drives extracellular electron transfer in response to transient limitations of electron acceptor or donor, with implications for the study of pathogens and industrial bioprocesses. Due to their low electroactivity, such populations are difficult to grow in bioelectrochemical systems and characterise with electrochemistry. Here, a critical review of recent research on weak electricigens is provided, with a focus on the methodology and the overall relevance to microbial ecology and bioelectrochemical systems.