Microsystems for biofilm characterization and sensing - A review

Electrochemical techniques for label-free and early detection of growing microbial cells and biofilms

Over the past decades, the misuse or abuse of antimicrobial agents to prevent and/or control infections has led to increased resistance of microbes to treatments, and antimicrobial resistance is now a subject of major global concern. In some cases, microbes possess the capacity to attach to biotic or abiotic surfaces, and to produce a protective polymeric matrix, forming biofilms of higher resistance and virulence compared to planktonic forms. To avoid further excessive and inappropriate use of antimicrobials, and to propose new effective treatments, it is very important to detect planktonic microbes and microbial biofilms in their early growth stage and at the point of need. In this review, we provide an overview of currently available electrochemical techniques, in particular impedimetric and voltamperometric methods, highlighting recent advances in the field and illustrating with examples in antibiotic susceptibility testing and microbial biofilm monitoring.

Novel Antibacterial Agents SAAP-148 and Halicin Combat Gram-Negative Bacteria Colonizing Catheters

The antibiotic management of catheter-related infections (CRIs) often fails owing to the emergence of antimicrobial-resistant strains and/or biofilm/persister apparitions. Thus, we investigated the efficacy of two novel antimicrobial agents, i.e., the synthetic peptide SAAP-148 and the novel antibiotic halicin, against Gram-negative bacteria (GNB) colonizing catheters. The antibacterial, anti-biofilm, and anti-persister activities of both agents were evaluated against Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae strains. The enrolled strains were isolated from catheters and selected based on their resistance to at least three antibiotic classes and biofilm formation potential. Furthermore, the hemolysis and endotoxin neutralization abilities of these agents were explored. The bactericidal activity of both agents was reduced in urine and plasma as compared to buffered saline. In a dose-dependent manner, SAAP-148 and halicin reduced bacterial counts in 24 h preformed biofilms on silicone elastomer discs and eliminated persisters originating from antibiotic-exposed mature 7-day biofilms, with halicin being less effective than SAAP-148. Importantly, SAAP-148 and halicin acted synergistically on E. coli and K. pneumoniae biofilms but not on A. baumannii biofilms. The peptide, but not halicin, decreased the production of IL-12p40 upon exposure to UV-killed bacteria. This preliminary study showed that SAAP-148 and halicin alone/in combination are promising candidates to fight GNB colonizing catheters.

How to study biofilms: technological advancements in clinical biofilm research

Biofilm formation is an important survival strategy commonly used by bacteria and fungi, which are embedded in a protective extracellular matrix of organic polymers. They are ubiquitous in nature, including humans and other animals, and they can be surface- and non-surface-associated, making them capable of growing in and on many different parts of the body. Biofilms are also complex, forming polymicrobial communities that are difficult to eradicate due to their unique growth dynamics, and clinical infections associated with biofilms are a huge burden in the healthcare setting, as they are often difficult to diagnose and to treat. Our understanding of biofilm formation and development is a fast-paced and important research focus. This review aims to describe the advancements in clinical biofilm research, including both in vitro and in vivo biofilm models, imaging techniques and techniques to analyse the biological functions of the biofilm.

Thin-Film Waveguide Laser Spectroscopy: A Novel Platform for Bacterial Analysis

Bacterial sensing based on quantum cascade laser spectroscopy coupled with diamond or gallium arsenide thin-film waveguides is a novel analytical tool for gaining high-resolution infrared spectroscopic information of planktonic and sessile bacteria, as shown in the present study for Escherichia coli. During observation periods of up to 24 h, diamond and gallium arsenide thin-film waveguide laser spectroscopy was compared to information obtained via conventional Fourier transform infrared spectroscopy. The proliferation behavior of E. coli at those surfaces was complementarily investigated using atomic force microscopy and scanning electron microscopy.

Challenges and current advances in in vitro biofilm characterization

Biofilms are structured communities of bacterial cells encased in a self-produced polymeric matrix, which develop over time and exhibit temporal responses to stimuli from internal biological processes or external environmental changes. They can be detrimental, threatening public health and causing economic loss, while they also play beneficial roles in ecosystem health, biotechnology processes, and industrial settings. Biofilms express extreme heterogeneity in their physical properties and structural composition, resulting in critical challenges in understanding them comprehensively. The lack of detailed knowledge of biofilms and their phenotypes has deterred significant progress in developing strategies to control their negative impacts and take advantage of their beneficial applications. A range of in vitro models and characterization tools have been developed and used to study biofilm growth and, specifically, to investigate the impact of environmental and growth factors on their development. This review article discusses the existing knowledge of biofilm properties and explains how external factors, such as flow condition, surface, interface, and host factor, may impact biofilm growth. The limitations of current tools, techniques, and in vitro models that are currently used for biofilms are also presented.

Microalgae cell adhesions on hydrophobic membrane substrates using quartz crystal microbalance with dissipation

Microalgal cell adhesion and biofilm formation are affected by interactions between microalgae strains and membrane materials. Variations of surface properties of microalgae and membrane materials are expected to affect cell-membranes and cell-cell interactions and thus initial microalgal cell adhesion and biofilm formation rates. Hence, it should be possible to identify the dominant mechanisms controlling microalgal cell adhesion and biofilm formation. The effects of surface properties of three different microalgal strains and three different types of membrane materials on microalgal cell adhesion and biofilm formation were systematically investigated in real time by monitoring changes in the oscillation frequency and dissipation of the quartz crystal resonator (QCM-D). The results revealed that in general a higher surface free energy, more negative zeta potential, and higher surface roughness of membrane materials positively correlated with a larger quantity of microalgae cell deposition, while a more hydrophilic microalgae with a larger negative zeta potential preferred to attach to a more hydrophobic membrane material. The adhered microalgal layers exhibited viscoelastic properties. The relative importance of these mechanisms in controlling microalgae cell attachment and biofilm formation might vary, depending on the properties of specific microalgae species and hydrophobic membrane materials used.

Applications of Lab on a Chip in Antimicrobial Susceptibility of Staphylococcus aureus: A Systematic Review

Background and Objectives: Staphylococcus aureus is a prevalent bacterium capable of inducing various infections, including skin and soft tissue infections, bloodstream infections, pneumonia, and surgical site infections. The emergence of antimicrobial resistance in S. aureus, particularly methicillin-resistant S. aureus, has raised substantial concerns within global healthcare settings. Prior to antibiotic prescription, the ideal approach is antimicrobial susceptibility testing (AST); however, this is frequently perceived as excessively complex and time-intensive. Lab-on-a-chip (LOC) technology holds promise in addressing these challenges and advancing fundamental microbiological research while also aiding in the development of therapeutic strategies. This systematic review aims to evaluate the potential utility of LOC for AST of S. aureus. Materials and Methods: This study adhered to the PRISMA guidelines. Various databases, including SCOPUS, PubMed/MEDLINE, SCIELO, and LILACS, in addition to gray literature sources, were employed in the review process. Results: Sixteen studies were included in this systematic review. All these studies detailed the effectiveness, rapidity, and predictability of LOC systems for assessing S. aureus susceptibility to various antibiotics. When comparing the LOC approach to traditional manual methods, it was evident that LOC requires a minimal quantity of reagents. Furthermore, most studies reported that the entire LOC procedure took 10 min to 7 h, with results being equally accurate as those obtained through traditional AST protocols. Conclusions: The potential application of LOC for AST of S. aureus is emphasized by its ability to provide rapid access to minimum inhibitory concentration data, which can substantially aid in selecting the most suitable antibiotics and dosages for treating challenging infections caused by this microorganism. Moreover, the rapid AST facilitated by LOC holds promise for enhancing the appropriateness and efficacy of therapy in clinical settings.

Non-aureus staphylococci and mammaliicocci as a cause of mastitis in domestic ruminants: current knowledge, advances, biomedical applications, and future perspectives - a systematic review

Non-aureus staphylococci and mammaliicocci (NASM) are one of the most common causes of subclinical mastitis in dairy animals and the extent of damage by intramammary infections (IMI) caused by NASM is still under debate. The different effects of NASM on the mammary gland may be associated with differences between bacterial species. NASM are normal and abundant colonizers of humans and animals and become pathogenic only in certain situations. The veterinary interest in NASM has been intense for the last 25 years, due to the strongly increasing rate of opportunistic infections. Therefore, the objective of this review is to provide a general background of the NASM as a cause of mastitis and the most recent advances that exist to prevent and fight the biofilm formation of this group of bacteria, introduce new biomedical applications that could be used in dairy herds to reduce the risk of chronic and recurrent infections, potentially responsible for economic losses due to reduced milk production and quality. Effective treatment of biofilm infection requires a dual approach through a combination of antibiofilm and antimicrobial agents. Even though research on the development of biofilms is mainly focused on human medicine, this technology must be developed at the same time in veterinary medicine, especially in the dairy industry where IMI are extremely common.

Antimicrobial Peptides Originating from Expression Libraries of Aurelia aurita and Mnemiopsis leidyi Prevent Biofilm Formation of Opportunistic Pathogens

The demand for novel antimicrobial compounds is rapidly growing due to the rising appearance of antibiotic resistance in bacteria; accordingly, alternative approaches are urgently needed. Antimicrobial peptides (AMPs) are promising, since they are a naturally occurring part of the innate immune system and display remarkable broad-spectrum activity and high selectivity against various microbes. Marine invertebrates are a primary resource of natural AMPs. Consequently, cDNA expression (EST) libraries from the Cnidarian moon jellyfish Aurelia aurita and the Ctenophore comb jelly Mnemiopsis leidyi were constructed in Escherichia coli. Cell-free size-fractionated cell extracts (<3 kDa) of the two libraries (each with 29,952 clones) were consecutively screened for peptides preventing the biofilm formation of opportunistic pathogens using the crystal violet assay. The 3 kDa fraction of ten individual clones demonstrated promising biofilm-preventing activities against Klebsiella oxytoca and Staphylococcus epidermidis. Sequencing the respective activity-conferring inserts allowed for the identification of small ORFs encoding peptides (10-22 aa), which were subsequently chemically synthesized to validate their inhibitory potential. Although the peptides are likely artificial products from a random translation of EST inserts, the biofilm-preventing effects against K. oxytoca, Pseudomonas aeruginosa, S. epidermidis, and S. aureus were verified for five synthetic peptides in a concentration-dependent manner, with peptide BiP_Aa_5 showing the strongest effects. The impact of BiP_Aa_2, BiP_Aa_5, and BiP_Aa_6 on the dynamic biofilm formation of K. oxytoca was further validated in microfluidic flow cells, demonstrating a significant reduction in biofilm thickness and volume by BiP_Aa_2 and BiP_Aa_5. Overall, the structural characteristics of the marine invertebrate-derived AMPs, their physicochemical properties, and their promising antibiofilm effects highlight them as attractive candidates for discovering new antimicrobials.

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.

Yeast biofilms on abiotic surfaces: Adhesion factors and control methods

Biofilms are highly resistant to antimicrobials and are a common problem in many industries, including pharmaceutical, food and beverage. Yeast biofilms can be formed by various yeast species, including Candida albicans, Saccharomyces cerevisiae, and Cryptococcus neoformans. Yeast biofilm formation is a complex process that involves several stages, including reversible adhesion, followed by irreversible adhesion, colonization, exopolysaccharide matrix formation, maturation and dispersion. Intercellular communication in yeast biofilms (quorum-sensing mechanism), environmental factors (pH, temperature, composition of the culture medium), and physicochemical factors (hydrophobicity, Lifshitz-van der Waals and Lewis acid-base properties, and electrostatic interactions) are essential to the adhesion process. Studies on the adhesion of yeast to abiotic surfaces such as stainless steel, wood, plastic polymers, and glass are still scarce, representing a gap in the field. The biofilm control formation can be a challenging task for food industry. However, some strategies can help to reduce biofilm formation, such as good hygiene practices, including regular cleaning and disinfection of surfaces. The use of antimicrobials and alternative methods to remove the yeast biofilms may also be helpful to ensure food safety. Furthermore, physical control measures such as biosensors and advanced identification techniques are promising for yeast biofilms control. However, there is a gap in understanding why some yeast strains are more tolerant or resistant to sanitization methods. A better understanding of tolerance and resistance mechanisms can help researchers and industry professionals to develop more effective and targeted sanitization strategies to prevent bacterial contamination and ensure product quality. This review aimed to identify the most important information about yeast biofilms in the food industry, followed by the removal of these biofilms by antimicrobial agents. In addition, the review summarizes the alternative sanitizing methods and future perspectives for controlling yeast biofilm formation by biosensors.

Real-Time Biosensing Bacteria and Virus with Quartz Crystal Microbalance: Recent Advances, Opportunities, and Challenges

Continuous monitoring of pathogens finds applications in environmental, medical, and food industry settings. Quartz crystal microbalance (QCM) is one of the promising methods for real-time detection of bacteria and viruses. QCM is a technology that utilizes piezoelectric principles to measure mass and is commonly used in detecting the mass of chemicals adhering to a surface. Due to its high sensitivity and rapid detection times, QCM biosensors have attracted considerable attention as a potential method for detecting infections early and tracking the course of diseases, making it a promising tool for global public health professionals in the fight against infectious diseases. This review first provides an overview of the QCM biosensing method, including its principle of operation, various recognition elements used in biosensor creation, and its limitations and then summarizes notable examples of QCM biosensors for pathogens, focusing on microfluidic magnetic separation techniques as a promising tool in the pretreatment of samples. The review explores the use of QCM sensors in detecting pathogens in various samples, such as food, wastewater, and biological samples. The review also discusses the use of magnetic nanoparticles for sample preparation in QCM biosensors and their integration into microfluidic devices for automated detection of pathogens and highlights the importance of accurate and sensitive detection methods for early diagnosis of infections and the need for point-of-care approaches to simplify and reduce the cost of operation.

Real-time in-situ electrochemical monitoring of Pseudomonas aeruginosa biofilms grown on air-liquid interface and its antibiotic susceptibility using a novel dual-chamber microfluidic device

Biofilms are communities of bacterial cells encased in a self-produced polymeric matrix that exhibit high tolerance toward environmental stress. Despite the plethora of research on biofilms, most P. aeruginosa biofilm models are cultured on a solid-liquid interface, and the longitudinal growth characteristics of P. aeruginosa biofilm are unclear. This study demonstrates the real-time and noninvasive monitoring of biofilm growth using a novel dual-chamber microfluidic device integrated with electrochemical detection capabilities to monitor pyocyanin (PYO). The growth of P. aeruginosa biofilms on the air-liquid interface (ALI) was monitored over 48 h, and its antibiotic susceptibility to 6 h exposure of 50, 400, and 1600 µg/ml of ciprofloxacin solutions was analyzed. The biofilm was treated directly on its surface and indirectly from the substratum by delivering the CIP solution to the top or bottom chamber of the microfluidic device. Results showed that P. aeruginosa biofilm developed on ALI produces PYO continuously, with the PYO production rate varying longitudinally and peak production observed between 24 and 30 h. In addition, this current study shows that the amount of PYO produced by the ALI biofilm is proportional to its viable cell numbers, which has not been previously demonstrated. Biofilm treated with ciprofloxacin solution above 400 µg/ml showed significant PYO reduction, with biofilms being killed more effectively when treatment was applied to their surfaces. The electrochemical measurement results have been verified with colony-forming unit count results, and the strong correlation between the PYO electrical signal and the viable cell number highlights the usefulness of this approach for fast and low-cost ALI biofilm study and antimicrobial tests.

Ultraviolet control of bacterial biofilms in microfluidic chips

Polydimethylsiloxane (PDMS) microfluidic systems have been instrumental in better understanding couplings between physical mechanisms and bacterial biofilm processes, such as hydrodynamic effects. However, precise control of the growth conditions, for example, the initial distribution of cells on the substrate or the boundary conditions in a flow system, has remained challenging. Furthermore, undesired bacterial colonization in crucial parts of the systems, in particular, in mixing zones or tubing, is an important factor that strongly limits the duration of the experiments and, therefore, impedes our ability to study the biophysics of biofilm evolving over long periods of time, as found in the environment, in engineering, or in medicine. Here, we develop a new approach that uses ultraviolet-C (UV-C) light-emitting diodes (LEDs) to confine bacterial development to specific zones of interest in the flow channels. The LEDs are integrated into a 3D printed light guide that is positioned upon the chip and used to irradiate germicidal UV-C directly through the PDMS. We first demonstrate that this system is successful in controlling undesired growth of Pseudomonas aeruginosa biofilm in inlet and outlet mixing zones during 48 h. We further illustrate how this can be used to define the initial distribution of bacteria to perturb already formed biofilms during an experiment and to control colonization for seven days-and possibly longer periods of time-therefore opening the way toward long-term biofilm experiments in microfluidic devices. Our approach is easily generalizable to existing devices at low cost and may, thus, become a standard in biofilm experiments in PDMS microfluidics.

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.

Real-Time Monitoring of Biofilm Formation Using a Noninvasive Impedance-Based Method

Biofilms are complex three-dimensional microbial communities that adhere to a variety of surfaces and interact with their surroundings. Because of the dynamic nature of biofilm formation, establishing a uniform technique for quantifying and monitoring biofilm volume, shape, and features in real-time is challenging. Herein, we describe a noninvasive electrochemical impedance approach for real-time monitoring of dental plaque-derived multispecies biofilm growth on a range of substrates. A working equation relating electrochemical impedance to live biofilm volume has been developed that is applicable to all three surfaces examined, including glass, dental filling resin, and Ca2+-releasing resin composites. Impedance changes of 2.5, 35, 50, and 65% correlated to biofilm volumes of 0.10 ± 0.01, 16.9 ± 2.2, 29.7 ± 2.3, and 38.6 ± 2.8 μm3/μm2, respectively. We discovered that glass, dental filling resin, and Ca2+-releasing dental composites required approximately 3.5, 4.5, and 6 days, respectively, to achieve a 50% change in impedance. The local pH change at the biofilm-substrate interfaces also monitored with potentiometry pH microsensor, and pH change varied according to biofilm volume. This impedance-based technique can be a useful analytical method for monitoring the growth of biofilms on a variety of substrates in real-time. Therefore, this technique may be beneficial for examining antibacterial properties of novel biomaterials.

Mitigation and use of biofilms in space for the benefit of human space exploration

Biofilms are self-organized communities of microorganisms that are encased in an extracellular polymeric matrix and often found attached to surfaces. Biofilms are widely present on Earth, often found in diverse and sometimes extreme environments. These microbial communities have been described as recalcitrant or protective when facing adversity and environmental exposures. On the International Space Station, biofilms were found in human-inhabited environments on a multitude of hardware surfaces. Moreover, studies have identified phenotypic and genetic changes in the microorganisms under microgravity conditions including changes in microbe surface colonization and pathogenicity traits. Lack of consistent research in microgravity-grown biofilms can lead to deficient understanding of altered microbial behavior in space. This could subsequently create problems in engineered systems or negatively impact human health on crewed spaceflights. It is especially relevant to long-term and remote space missions that will lack resupply and service. Conversely, biofilms are also known to benefit plant growth and are essential for human health (i.e., gut microbiome). Eventually, biofilms may be used to supply metabolic pathways that produce organic and inorganic components useful to sustaining life on celestial bodies beyond Earth. This article will explore what is currently known about biofilms in space and will identify gaps in the aerospace industry's knowledge that should be filled in order to mitigate or to leverage biofilms to the advantage of spaceflight.

Non-invasive biomedical sensors for early detection and monitoring of bacterial biofilm growth at the point of care

Bacterial infections have long been a serious global health issue. Biofilm formation complicates matters even more. The biofilm's extracellular polymeric substances (EPSs) matrix protects bacteria from the host's immune responses, yielding strong adhesion and drug resistance as the biofilm matures. Early bacterial biofilm detection and bacterial biofilm growth monitoring are crucial to treating biofilm-associated infections. Current detection methods are highly sensitive but not portable, are time-consuming, and require expensive equipment and complex operating procedures, limiting their use at the point of care. Therefore, there is an urgent need to develop affordable, on-body, and non-invasive biomedical sensors to continuously monitor and detect early biofilm growth at the point of care through personalized telemedicine. Herein, recent advances in developing non-invasive biomedical sensors for early detection and monitoring bacterial biofilm growth are comprehensively reviewed. First, biofilm's life cycle and its impact on the human body, such as biofilm-associated disease and infected medical devices, are introduced together with the challenges of biofilm treatment. Then, the current methods used in clinical and laboratory settings for biofilm detection and their challenges are discussed. Next, the current state of non-invasive sensors for direct and indirect detection of bacterial biofilms are summarized and highlighted with the detection parameters and their design details. Finally, commercially available products, challenges of current devices, and the further trend in biofilm detection sensors are discussed.

Flexible biofilm monitoring device

Biofilms and their analysis are increasingly attracting the attention of the scientific community due to the immense importance and impact of biofilms in various natural, technical and medical fields. For these purposes, an optimized and extended antibiofilm assay system based on the Calgary Biofilm Device (MBEC Assay® system) consisting of microtiter plate and PCR tubes was established. Its implementation was used to study the growth characteristics of the sessile phenotype of Pseudomonas fluorescens exposed to antimicrobial peptides. Inhibitory effects of an antimicrobial peptide on P. fluorescens biofilm formation could be determined at a concentration of 250 μg/ml (biofilm prevention concentration (BPC)) using the modified biofilm assay. Similarly, the biofilm bactericidal concentration (BBC) at 125 μg/ml and the minimum biofilm elimination concentration to remove 90% of the total biofilm mass (MBEC90) were measured at a concentration range of 15.625-1.95 μg/ml. In conclusion, this optimized system provides a highly variable, simple, and cost-effective alternative to high-throughput screening based on the Calgary Biofilm Device (CBD).

Effect of Biosynthesized Silver Nanoparticles on Bacterial Biofilm Changes in S. aureus and E. coli

One approach for solving the problem of antibiotic resistance and bacterial persistence in biofilms is treatment with metals, including silver in the form of silver nanoparticles (AgNPs). Green synthesis is an environmentally friendly method to synthesize nanoparticles with a broad spectrum of unique properties that depend on the plant extracts used. AgNPs with antibacterial and antibiofilm effects were obtained using green synthesis from plant extracts of Lagerstroemia indica (AgNPs_LI), Alstonia scholaris (AgNPs_AS), and Aglaonema multifolium (AgNPs_AM). Nanoparticles were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) analysis. The ability to quench free radicals and total phenolic content in solution were also evaluated. The antibacterial activity of AgNPs was studied by growth curves as well as using a diffusion test on agar medium plates to determine minimal inhibitory concentrations (MICs). The effect of AgNPs on bacterial biofilms was evaluated by crystal violet (CV) staining. Average minimum inhibitory concentrations of AgNPs_LI, AgNPs_AS, AgNPs_AM were 15 ± 5, 20 + 5, 20 + 5 μg/mL and 20 ± 5, 15 + 5, 15 + 5 μg/mL against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, respectively. The E. coli strain formed biofilms in the presence of AgNPs, a less dense biofilm than the S. aureus strain. The highest inhibitory and destructive effect on biofilms was exhibited by AgNPs prepared using an extract from L. indica.

A Microfluidic Chip for Studies of the Dynamics of Antibiotic Resistance Selection in Bacterial Biofilms

Biofilms are arguably the most important mode of growth of bacteria, but how antibiotic resistance emerges and is selected in biofilms remains poorly understood. Several models to study evolution of antibiotic resistance have been developed, however, their usability varies depending on the nature of the biological question. Here, we developed and validated a microfluidic chip (Brimor) for studying the dynamics of enrichment of antibiotic-resistant bacteria in biofilms using real-time monitoring with confocal microscopy. In situ extracellular cellulose staining and physical disruption of the biomass confirmed Escherichia coli growth as biofilms in the chip. We showed that seven generations of growth occur in 16 h when biofilms were established in the growth chambers of Brimor, and that bacterial death and growth rates could be estimated under these conditions using a plasmid with a conditional replication origin. Additionally, competition experiments between antibiotic-susceptible and -resistant bacteria at sub-inhibitory concentrations demonstrated that the antibiotic ciprofloxacin selected for antibiotic resistance in bacterial biofilms at concentrations 17-fold below the minimal inhibitory concentration of susceptible planktonic bacteria. Overall, the microfluidic chip is easy to use and a relevant model for studying the dynamics of selection of antibiotic resistance in bacterial biofilms and we anticipate that the Brimor chip will facilitate basic research in this area.

Forward-Looking Roadmaps for Long-Term Continuous Water Quality Monitoring: Bottlenecks, Innovations, and Prospects in a Critical Review

Long-term continuous monitoring (LTCM) of water quality can bring far-reaching influences on water ecosystems by providing spatiotemporal data sets of diverse parameters and enabling operation of water and wastewater treatment processes in an energy-saving and cost-effective manner. However, current water monitoring technologies are deficient for long-term accuracy in data collection and processing capability. Inadequate LTCM data impedes water quality assessment and hinders the stakeholders and decision makers from foreseeing emerging problems and executing efficient control methodologies. To tackle this challenge, this review provides a forward-looking roadmap highlighting vital innovations toward LTCM, and elaborates on the impacts of LTCM through a three-hierarchy perspective: data, parameters, and systems. First, we demonstrate the critical needs and challenges of LTCM in natural resource water, drinking water, and wastewater systems, and differentiate LTCM from existing short-term and discrete monitoring techniques. We then elucidate three steps to achieve LTCM in water systems, consisting of data acquisition (water sensors), data processing (machine learning algorithms), and data application (with modeling and process control as two examples). Finally, we explore future opportunities of LTCM in four key domains, water, energy, sensing, and data, and underscore strategies to transfer scientific discoveries to general end-users.

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.

Microfluidic devices for studying bacterial taxis, drug testing and biofilm formation

Some bacteria have coevolved to establish symbiotic or pathogenic relationships with plants, animals or humans. With human association, the bacteria can cause a variety of diseases. Thus, understanding bacterial phenotypes at the single-cell level is essential to develop beneficial applications. Traditional microbiological techniques have provided great knowledge about these organisms; however, they have also shown limitations, such as difficulties in culturing some bacteria, the heterogeneity of bacterial populations or difficulties in recreating some physical or biological conditions. Microfluidics is an emerging technique that complements current biological assays. Since microfluidics works with micrometric volumes, it allows fine-tuning control of the test conditions. Moreover, it allows the recruitment of three-dimensional (3D) conditions, in which several processes can be integrated and gradients can be generated, thus imitating physiological 3D environments. Here, we review some key microfluidic-based studies describing the effects of different microenvironmental conditions on bacterial response, biofilm formation and antimicrobial resistance. For this aim, we present different studies classified into six groups according to the design of the microfluidic device: (i) linear channels, (ii) mixing channels, (iii) multiple floors, (iv) porous devices, (v) topographic devices and (vi) droplet microfluidics. Hence, we highlight the potential and possibilities of using microfluidic-based technology to study bacterial phenotypes in comparison with traditional methodologies.

In Silico Screening and In Vitro Assessment of Natural Products with Anti-Virulence Activity against Helicobacter pylori

Helicobacter pylori is one of the most frequent human pathogens and a leading etiological agent of various gastric diseases. As stringent response, coordinated by a SpoT protein, seems to be crucial for the survivability of H. pylori, the main goal of this article was to use in silico computational studies to find phytochemical compounds capable of binding to the active site of SpoT from H. pylori and confirm the ability of the most active candidates to interfere with the virulence of this bacterium through in vitro experiments. From 791 natural substances submitted for the virtual screening procedure, 10 were chosen and followed for further in vitro examinations. Among these, dioscin showed the most interesting parameters (the lowest MIC, the highest anti-biofilm activity in static conditions, and a relatively low stimulation of morphological transition into coccoids). Therefore, in the last part, we extended the research with a number of further experiments and observed the ability of dioscin to significantly reduce the formation of H. pylori biofilm under Bioflux-generated flow conditions and its capacity for additive enhancement of the antibacterial activity of all three commonly used antibiotics (clarithromycin, metronidazole, and levofloxacin). Based on these results, we suggest that dioscin may be an interesting candidate for new therapies targeting H. pylori survivability and virulence.

Antibiofilm and Antimicrobial-Enhancing Activity of Chelidonium majus and Corydalis cheilanthifolia Extracts against Multidrug-Resistant Helicobacter pylori

Helicobacter pylori is a Gram-negative bacterium that colonizes the stomach of about 60% of people worldwide. The search for new drugs with activity against H. pylori is now a hotspot in the effective and safe control of this bacterium. Therefore, the aim of this research was to determine the antibacterial activity of extracts from selected plants of the Papaveraceae family against planktonic and biofilm forms of the multidrug-resistant clinical strain of H. pylori using a broad spectrum of analytical in vitro methods. It was revealed that among the tested extracts, those obtained from Corydalis cheilanthifolia and Chelidonium majus were the most active, with minimal inhibitory concentrations (MICs) of 64 µg/mL and 128 µg/mL, respectively. High concentrations of both extracts showed cytotoxicity against cell lines of human hepatic origin. Therefore, we attempted to lower their MICs through the use of a synergistic combination with synthetic antimicrobials as well as by applying cellulose as a drug carrier. Using checkerboard assays, we determined that both extracts presented synergistic interactions with amoxicillin (AMX) and 3-bromopyruvate (3-BP) (FICI = 0.5) and additive relationships with sertraline (SER) (FICI = 0.75). The antibiofilm activity of extracts and their combinations with AMX, 3-BP, or SER, was analyzed by two methods, i.e., the microcapillary overgrowth under flow conditions (the Bioflux system) and assessment of the viability of lawn biofilms after exposure to drugs released from bacterial cellulose (BC) carriers. Using both methods, we observed a several-fold decrease in the level of H. pylori biofilm, indicating the ability of the tested compounds to eradicate the microbial biofilm. The obtained results indicate that application of plant-derived extracts from the Papaveraceae family combined with synthetic antimicrobials, absorbed into organic BC carrier, may be considered a promising way of fighting biofilm-forming H. pylori.

An antifouling polymer for dynamic anti-protein adhesion analysis by a quartz crystal microbalance

Nowadays, the non-specific adsorption of biomolecules is a key issue in numerous fields. Herein, an improved antifouling molecule was synthesized by grafting phenol with oligopoly (ethylene glycol), named (4-(2-(2-ethoxyethoxy) ethoxy) phenol (EEP). An ideal antifouling polymer coating (PEEP) was synthesized by the mechanism of electropolymerization of phenol. Quartz crystal microbalance (QCM), a sensitive mass sensor, was used to dynamically monitor both the modification and anti-protein adhesion (with bovine serum albumin as the model) process. Quantitatively, less proteins were observed to adhere to the modified electrode (277.8 ng for bare GCE and 8.88 ng for the modified GCE). Fourier transform infrared spectrophotometry (FT-IR), scanning electron microscopy (SEM), and electrochemical methods were used to study the coatings in detail. In this study, EEP was synthesized for the electrochemical preparation of an antifouling coating and characterized by QCM and electrochemical methods. The mild preparation environment (lower potential window and in phosphate buffered saline) and one-step method enable potential applications of PEEP in the field of biomaterials and biosensors.

CONTROL DE Aedes aegypti (DIPTERA: CULICIDAE) MEDIANTE ACTINOBACTERIAS FORMADORAS DE BIOPELÍCULAS

El phylum Actinobacteria incluye miembros productores de compuestos bioinsecticidas. No obstante, la sobreexplotacion de metabolitos derivados de Streptomyces ha conllevado a explorar nuevas moléculas provenientes de bacterias no estreptomicetos para contrarrestar la resistencia a insecticidas químicos en Aedes aegypti. Concordantes con el uso de bioagentes ecológicos, esta investigación caracterizó actinobacterias formadoras de biopelículas con el fin de evaluar su dinámica de crecimiento, actividad larvicida y efectos subletales. La identificación, crecimiento de biopelículas y bioactividades se realizaron por cultivos, análisis de imágenes por fotomicrografía y bioensayos. Los resultados mostraron que las biopelículas pertenecen a Pseudonocardiaceae (PsA1TA) y Corynebacteriaceae (CoA2CA) característicamente dependientes del revestimiento cuticular. PsA1TA coloniza estructuras membranosas de tórax y abdomen con microcolonias aleatoriamente distribuidas que desarrollan a extensas biopelículas mono y biestratificadas, al cubrir cuatro veces la amplitud toracoabdominal (envergadura infectiva entre 1010 µm a 1036 µm). En contraste, CoA2CA envuelve radialmente estructuras esclerotizadas cefálica y anal al triplicar la amplitud de tales órganos (1820 a 2030 µm y 1650 a 1860 µm, respectivamente). Las biopelículas ejercieron mortalidad diferenciada a todos los estadios larvales, no obstante, PsA1TA resultó más mortal y virulento en el segundo estadio larval (58 %-96 horas, TL50: 3,4 días), mientras que CoA2CA lo fue en el cuarto estadio larval (85 %-96 horas, TL50: 2,5 días). CoA2CA indujo emergencia incompleta de adultos farados y despliegue de tarsos curvos en emergentes, además de revestir con robustas biopelículas cadáveres larvarios. Las biopelículas actinobacterianas revelaron ejercer función larvicida y respuestas subletales en A. aegypti.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Modeling the impact of evolving biofilms on flow in porous media inside a microfluidic channel

This study integrates microfluidic experiments and mathematical modeling to study the impacts of biofilms on flow in porous media and to explore approaches to simplify modeling permeability with complicated biofilm geometries. E. coli biofilms were grown in a microfluidic channel packed with a single layer of glass beads to reach three biofilm levels: low, intermediate, and high, with biofilm ratios (β_r) of 2.7%, 17.6%, and 55.2%, respectively. Two-dimensional biofilm structures and distributions in the porous medium were modeled by digitizing confocal images and considering broad ranges of biofilm permeability (k_b) (from 10^-15 m² to 10^-7 m²) and biofilm porosity (ε_b) (from 0.2 to 0.8). The overall permeability of the porous medium (k), the flow pathways and the overall/local pressure gradients were found to be highly dependent on β_r and k_b but were moderately impacted by ε_b when the biofilm levels were high and intermediate with k_b>10^-11 m². When biofilm structures are well developed, simplified biofilm geometries, such as uniform coating and symmetric contact filling, can provide reasonable approximations of k.

The evolution from the two stage to the one stage procedure for biofilm based periprosthetic joint infections (PJI)

A definitive consensus on the optimal limb salvage protocol for infected total joints does not currently exist. Popular, is the two-stage revision which calls for the use of an antibiotic loaded spacer followed by a delayed exchange. Our question is whether single-stage revisions for biofilm based infected arthroplasties results in comparable or possibly better patient outcomes as compared to those reported for two-stage revisions. We retrospectively reviewed 500 cases of one-stage revisions for periprosthetic joint infections (PJI) using dual setup with radical debridement, definitive reconstruction with antibiotic loaded cement and implantation of antibiotic calcium sulfate pellets between the years 2005-2017. The revisions included 351 total knees, 122 hips, 2 hip-femur-knees, 13 shoulders, 10 elbows, and 2 shoulder-humerus-elbows. The patient population had a mean follow-up of 60 months (range: 24 months-14 years) and mean patient age of 61 years old, consisting of 250 males and 250 females. Patient comorbidities were reviewed, classified using McPherson's staging for PJIs, and compared to the Cierny & Mader classification system. Successful treatment was defined as a joint without recurrence of infection, for a minimum of 2 years, and limb preservation. Based on our findings, one-stage revision of PJIs demonstrates at least as good an infection eradication rate as two-stage revision: 88% vs 85% respectively.