Influence of electric fields and pH on biofilm structure as related to the bioelectric effect

The treatment of bacterial biofilms cultivated on knee arthroplasty implants using the bioelectric effect

Introduction: The formation of bacterial biofilms on knee arthroplasty implants can have catastrophic consequences. The aim of this study was to analyze the effectiveness of the bioelectric effect in the elimination of bacterial biofilms on cultivated knee arthroplasty implants. Methods: A novel device was designed to deliver a bioelectric effect on the surface of knee arthroplasty implants. 4-femoral prosthetic implants were cultivated with a staphylococcus aureus inoculum for 15 days. The components were divided into four different groups: A (not treated), B (normal saline 20-minutes), C (bioelectric effect 10-minutes), D (bioelectric effect 20-minutes). The implants were sonicated, and the detached colonies were quantified as the number of colony-forming unit (CFUs). The implants were sterilised and the process was repeated in a standardized manner four more times, to obtain a total of five samples per group. Results: The number of the CFUs after a 10-minute exposure to the bioelectric effect was of 208.2 ± 240.4, compared with 6,041.6 ± 2010.7 CFUs in group A, representing a decrease of 96.5% ± 4.3 (p = 0.004). And a diminution of 91.8% ± 7.9 compared with 2,051.0 ± 1,364.0 CFUs in group B (p = 0.109). The number of bacterial colonies after a 20-minute exposure to the bioelectric effect was 70 ± 126.7 CFUs, representing a decrease of 98.9% ± 1.9 (p = 0.000) compared with group A. And a decrease of 97.8% ± 3.0 (p = 0.019) compared with group B. Conclusions: The bioelectric effect was effective in the elimination of bacterial biofilm from knee arthroplasty implants. This method could be used in the future as part of conventional surgical procedures.

Comparative Analysis of Plaque Removal and Wear between Electric-Mechanical and Bioelectric Toothbrushes

Effective oral care is important for maintaining a high quality of life. Therefore, plaque control can prevent the development and recurrence of periodontitis. Brushing with a toothbrush and toothpaste is a common way to remove plaque; however, excessive brushing or brushing with abrasive toothpaste can cause wear and tear on the dental crown. Hence, we aimed to quantitatively compare the plaque-removal efficiency and tooth wear of toothbrushes using the bioelectric effect (BE) with those of electric-mechanical toothbrushes. To generate the BE signal, an electronic circuit was developed and embedded in a toothbrush. Further, typodonts were coated with cultured artificial plaques and placed in a brushing simulator. A toothpaste slurry was applied, and the typodonts were eluted with tap water after brushing. The plaques of the typodonts were captured, and the images were quantified. For the tooth wear experiment, polymethyl methacrylate disk resin blocks were brushed twice a day, and the thickness of the samples was measured. Subsequently, statistical differences between the experimental toothbrushes and typical toothbrushes were analyzed. The BE toothbrush had a higher plaque-removal efficiency and could minimize tooth wear. This study suggests that the application of BE may be a new solution for oral care.

Environmental pollution removal using electrostimulation of microorganisms by alternative current

The entrance of some toxic and hazardous chemical agents such as antibiotics, pesticides, and herbicides into the environment can cause various problems to human health and the environment. In recent years, researchers have considered the use of electrostimulation in the processes of microbial metabolism and biological systems for the treatment of pollutants in the environment. Although several electrostimulation reports have been presented for pollutant removal, little attention has been paid to alternative current (AC) biostimulation. This study presents a systematic review of microbial electrostimulation using bioelectrochemical systems supplied with AC. The utilization of alternating current bioelectrochemical systems (ACBESs) has some advantages such as the provide of appropriate active biofilms in the electrodes due to the cyclical nature of the current and energy transfer in an appropriate manner on the electrode surfaces. Moreover, the ACBESs can reduce hydraulic time (HRT) under optimal conditions and reduce the cost of converting electricity using AC. In microbial electrostimulation, amplitude (AMPL), waveform, C/N, and current have a significant effect on increasing the removal efficiency of the pollutants. The obtained results of the meta-analysis illustrated that various pollutants such as phenol, antibiotics, and nitrate have been removed in an acceptable range of 96% using the ACBESs. Therefore, microbial electrostimulation using AC is a promising technology for the decomposition and removal of various pollutants. Moreover, the ACBESs could provide new opportunities for promoting various bioelectrochemical systems (BESs) for the production of hydrogen or methane.

A Study on the Biofilm Removal Efficacy of a Bioelectric Toothbrush

Effective oral care is a critical requirement to maintain a high quality of life. Most oral diseases are caused by plaque (oral biofilm), which is also correlated with systemic diseases. A common method to remove biofilm is brushing teeth with toothpaste. However, 3.5 billion people in the world have oral diseases, meaning that more efficient methods of removing biofilms are needed. We have developed a toothbrush that applies a bioelectric effect (BE) utilizing an electric force for biofilm removal. It demonstrated significantly higher biofilm removal efficiency than non-BE manual toothbrushes. Tests were performed in saline and toothpaste conditions using various pressures. Results showed that the BE toothbrush had a significantly higher biofilm removal efficiency in saline (0.5 N: 215.43 ± 89.92%, 2.5 N: 116.77 ± 47.02%) and in a toothpaste slurry (0.5 N: 104.96 ± 98.93%, 2.5 N: 96.23 ± 35.16%) than non-BE manual toothbrushes. Results also showed that BE toothbrushes were less dependent on toothpaste. This study suggests that the application of BE can be a new solution to plaque problems in oral care.

Antimicrobial Efficiency of Chitosan and Its Methylated Derivative against Lentilactobacillus parabuchneri Biofilms

Antimicrobial materials are considered potential alternatives to prevent the development of biofilm-associated contaminations. Concerns regarding synthetic preservatives necessitate the development of innovative and safe natural antimicrobials. In the present study, we discuss the in situ infrared attenuated total reflection spectroscopy (IR-ATR) investigations of the selective antimicrobial efficiency of chitosan in controlling the growth of Lentilactobacillus parabuchneri biofilms. The protonated charges of chitosan were additionally amplified by structural modification via methylation, yielding quaternized derivative TMC (i.e., N, N, N-trimethyl chitosan). To evaluate antimicrobial effectiveness against L. parab. biofilms, IR-ATR spectroscopy provided information on molecular mechanisms and insights into chemical changes during real-time biofilm inhibition studies. The integrated fiberoptic oxygen microsensors enabled monitoring oxygen (O₂) concentration gradients within biofilms, thereby confirming the metabolic oxygen depletion dropping from 4.5 to 0.7 mg L^-1. IR studies revealed strong electrostatic interactions between chitosan/its water-soluble derivative and bacteria, indicating that a few hours were sufficient to affect biofilm disruption. The significant decrease in the IR bands is related to the characteristic spectral information of amide I, II, III, nucleic acid, and extracellular polymeric matrix (EPS) produced by L. parabuchneri biofilms. Cell clusters of biofilms, microcolonies, and destabilization of the EPS matrix after the addition of biopolymers were visualized using optical microscopy. In addition, scanning electron microscopy (SEM) of biofilms grown on polystyrene and stainless-steel surfaces was used to examine morphological changes, indicating the disintegration of the biofilm matrix into individual cells. Quantification of the total biofilm formation correlated with the CV assay results, indicating cell death and lysis. The electrostatic interactions between chitosan and the bacterial cell wall typically occur between protonated amino groups and negatively charged phospholipids, which promote permeabilization. Biofilm growth inhibition was assessed by a viability assay for a period of 72 h and in the range of low MIC values (varying 0.01-2%). These results support the potential of chitosan and TMC for bacterial growth prevention of the foodborne contaminant L. parabuchneri in the dairy industry and for further implementation in food packaging.

In situ monitoring of Lentilactobacillus parabuchneri biofilm formation via real-time infrared spectroscopy

Foodborne pathogenic microorganisms form biofilms at abiotic surfaces, which is a particular challenge in food processing industries. The complexity of biofilm formation requires a fundamental understanding on the involved molecular mechanisms, which may then lead to efficient prevention strategies. In the present study, biogenic amine producing bacteria, i.e., Lentilactobacillus parabuchneri DSM 5987 strain isolated from cheese were studied in respect with biofilm formation, which is of substantial relevance given their contribution to the presence of histamine in dairy products. While scanning electron microscopy was used to investigate biofilm adhesion at stainless steel surfaces, in situ infrared attenuated total reflection spectroscopy (IR-ATR) using a custom flow-through assembly was used for real-time and non-destructive observations of biofilm formation during a period of several days. The spectral window of 1700-600 cm-1 provides access to vibrational signatures characteristic for identifying and tracking L. parabuchneri biofilm formation and maturation. Especially, the amide I and II bands, lactic acid produced as the biofilm matures, and a pronounced increase of bands characteristic for extracellular polymeric substances (EPS) provide molecular insight into biofilm formation, maturation, and changes in biofilm architecture. Finally, multivariate data evaluation strategies were applied facilitating the unambiguous classification of the observed biofilm changes via IR spectroscopic data.

Reduction of biofilm accumulation by constant and alternating potentials in static and dynamic field experiments

The application of electric fields to conductive coatings is an environmentally friendly way to reduce biofilm formation. In particular alternating potentials (APs) have received increasing attention in recent studies. Here, an electrochemical rotating disk setup for dynamic field exposure experiments was developed to study how APs alter the attachment of fouling organisms in a multispecies ocean environment. A specific focus of the device design was proper integration of the potentiostat in the strongly corroding saltwater environment. The effect of APs on the accumulation of fouling organisms in short term field exposures was studied. Potentials on conductive gold surfaces were periodically switched between -0.3 V and 0.3 V or between -0.8 V and 0.6 V at a frequency of 0.5 Hz. APs were capable of significantly reducing the attachment of marine fouling organisms compared with the conductive samples immersed at open circuit potentials.

Control of Marine Bacteria and Diatom Biofouling by Constant and Alternating Potentials

The application of electrochemical potentials to surfaces is an easy and direct way to alter surface charge density, the structure of the electrochemical double layer, and the presence of electrochemically activated species. On such electrified interfaces the formation of biofilms is reduced. Here we investigate how applied potentials alter the colonization of surfaces by the marine bacterium Cobetia marina and the marine diatom Navicula perminuta. Different constant potentials between -0.8 and 0.6 V as well as regular switching between two potentials were investigated, and their influence on the attachment of the two biofilm-forming microorganisms on gold-coated working electrodes was quantified. Reduced bacteria and diatom attachment were found when negative potentials and alternating potentials were applied. The results are discussed on the basis of the electrochemical processes occurring at the working electrode in artificial seawater as revealed by cyclic voltammetry.

Fluorescent nanosensors reveal dynamic pH gradients during biofilm formation

Understanding the dynamic environmental microniches of biofilms will permit us to detect, manage and exploit these communities. The components and architecture of biofilms have been interrogated in depth; however, little is known about the environmental microniches present. This is primarily because of the absence of tools with the required measurement sensitivity and resolution to detect these changes. We describe the application of ratiometric fluorescent pH-sensitive nanosensors, as a tool, to observe physiological pH changes in biofilms in real time. Nanosensors comprised two pH-sensitive fluorophores covalently encapsulated with a reference pH-insensitive fluorophore in an inert polyacrylamide nanoparticle matrix. The nanosensors were used to analyse the real-time three-dimensional pH variation for two model biofilm formers: (i) opportunistic pathogen Pseudomonas aeruginosa and (ii) oral pathogen Streptococcus mutans. The detection of sugar metabolism in real time by nanosensors provides a potential application to identify therapeutic solutions to improve oral health.

Potential strategies to prevent encrustations on urinary stents and catheters - thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Introduction: Urinary stents have been around for the last 4 decades, urinary catheters even longer. They are associated with infections, encrustation, migration, and patient discomfort. Research efforts to improve them have shifted onto molecular and cellular levels. ENIUS brought together translational scientists to improve urinary implants and reduce morbidity.Methods & materials: A working group within the ENIUS network was tasked with assessing future research lines for the improvement of urinary implants.Topics were researched systematically using Embase and PubMed databases. Clinicaltrials.gov was consulted for ongoing trials.Areas covered: Relevant topics were coatings with antibodies, enzymes, biomimetics, bioactive nano-coats, antisense molecules, and engineered tissue. Further, pH sensors, biodegradable metals, bactericidal bacteriophages, nonpathogenic uropathogens, enhanced ureteric peristalsis, electrical charges, and ultrasound to prevent stent encrustations were addressed.Expert opinion: All research lines addressed in this paper seem viable and promising. Some of them have been around for decades but are yet to proceed to clinical application (i.e. tissue engineering). Others are very recent and, at least in urology, still only conceptual (i.e. antisense molecules). Perhaps the most important learning point resulting from this pan-European multidisciplinary effort is that collaboration between all stakeholders is not only fruitful but also truly essential.

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.

Microampere Electric Current Causes Bacterial Membrane Damage and Two-Way Leakage in a Short Period of Time

Physical agents, such as low electric voltage and current, have recently gained attention for antimicrobial treatment due to their bactericidal capability. Although microampere electric current was shown to suppress the growth of bacteria, it remains unclear to what extent the microampere current damaged the bacterial membrane. Here, we investigated the membrane damage and two-way leakage caused by microampere electric current (≤100 μA) with a short exposure time (30 min). Based on MitoTracker staining, propidium iodide staining, filtration assays, and quantitative single-molecule localization microscopy, we observed significant membrane damage, which allowed two-way leakage of ions, small molecules, and proteins. This study paves the way to new development of antimicrobial applications for ultralow electric voltage and current.IMPORTANCE Although electric voltage and current have been studied for a long time in terms of their ability to suppress the growth of bacteria and to kill bacteria, increasing interest has been aroused more recently due to the prevalence of antibiotic resistance of microbes in past decades. Toward understanding the antimicrobial mechanism of low electric voltage and current, previous studies showed that treating bacteria with milliampere electric currents (≥5 mA) for ≥72 h led to significant damage of the bacterial membrane, which likely resulted in leakage of cellular contents and influx of toxic substances through the damaged membrane. However, it remains unclear to what extent membrane damage and two-way (i.e., inward and outward) leakage are caused by lower (i.e., microampere) electric current in a shorter time frame. In this work, we set out to answer this question. We observed that the membrane damage was caused by microampere electric current in half an hour, which allowed two-way leakage of ions, small molecules, and proteins.

Electrogenic Biofilm Development Determines Charge Accumulation and Resistance to pH Perturbation

The electrogenic biofilm and the bio-electrode interface are the key biocatalytic components in bioelectrochemical systems (BES) and can have a large impact on cell performance. This study used four different anodic carbons to investigate electrogenic biofilm development to determine the influence of charge accumulation and biofilm growth on system performance and how biofilm structure may mitigate against pH perturbations. Power production was highest (1.40 W/m3) using carbon felt, but significant power was also produced when felt carbon was open-circuit acclimated in a control reactor (0.95 W/m3). The influence of carbon material on electrogenic biofilm development was determined by measuring the level of biofilm growth, using sequencing to identify the microbial populations and confocal microscopy to understand the spatial locations of key microbial groups. Geobacter spp. were found to be enriched in closed-circuit operation and these were in close association with the carbon anode, but these were not observed in the open-circuit controls. Electrochemical analysis also demonstrated that the highest mid-point anode potentials were close to values reported for cytochromes from Geobacter sulfurreductans. Biofilm development was greatest in felt anodes (closed-circuit acclimated 1209 ng/μL DNA), and this facilitated the highest pseudo-capacitive values due to the presence of redox-active species, and this was associated with higher levels of power production and also served to mitigate against the effects of low-pH operation. Supporting carbon anode structures are key to electrogenic biofilm development and associated system performance and are also capable of protecting electrochemically active bacteria from the effects of environmental perturbations.

600-ns pulsed electric fields affect inactivation and antibiotic susceptibilities of Escherichia coli and Lactobacillus acidophilus

Cell suspensions of Escherichia coli and Lactobacillus acidophilus were exposed to 600-ns pulsed electric fields (nsPEFs) at varying amplitudes (Low-13.5, Mid-18.5 or High-23.5 kV cm⁻¹) and pulse numbers (0 (sham), 1, 5, 10, 100 or 1000) at a 1 hertz (Hz) repetition rate. The induced temperature rise generated at these exposure parameters, hereafter termed thermal gradient, was measured and applied independently to cell suspensions in order to differentiate inactivation triggered by electric field (E-field) from heating. Treated cell suspensions were plated and cellular inactivation was quantified by colony counts after a 24-hour (h) incubation period. Additionally, cells from both exposure conditions were incubated with various antibiotic-soaked discs to determine if nsPEF exposure would induce changes in antibiotic susceptibility. Results indicate that, for both species, the total delivered energy (amplitude, pulse number and pulse duration) determined the magnitude of cell inactivation. Specifically, for 18.5 and 23.5 kV cm⁻¹ exposures, L. acidophilus was more sensitive to the inactivation effects of nsPEF than E. coli, however, for the 13.5 kV cm⁻¹ exposures E. coli was more sensitive, suggesting that L. acidophilus may need to meet an E-field threshold before significant inactivation can occur. Results also indicate that antibiotic susceptibility was enhanced by multiple nsPEF exposures, as observed by increased zones of growth inhibition. Moreover, for both species, a temperature increase of ≤ 20 °C (89% of exposures) was not sufficient to significantly alter cell inactivation, whereas none of the thermal equivalent exposures were sufficient to change antibiotic susceptibility categories.

Electrochemical methods to enhance osseointegrated prostheses

Osseointegrated (OI) prosthetic limbs have been shown to provide an advantageous treatment option for amputees. In order for the OI prosthesis to be successful, the titanium implant must rapidly achieve and maintain proper integration with the bone tissue and remain free of infection. Electrochemical methods can be utilized to control and/or monitor the interfacial microenvironment where the titanium implant interacts with the biological system (host bone tissue or bacteria). This review will summarize the current understanding of how electrochemical modalities can influence bone tissue and bacteria with specific emphasis on applications where the metallic prosthesis itself can be utilized directly as a stimulating electrode for enhanced osseointegration and infection control. In addition, a summary of electrochemical impedance sensing techniques that could be used to potentially assess osseointegration and infection status of the metallic prosthesis is presented.

An improvised microtiter dish biofilm assay for non-invasive biofilm detection on microbial fuel cell anodes and studying biofilm growth conditions

Microbial life is predominantly observed as biofilms, which are a sessile aggregation of microbial cells formed in response to stress conditions. The microtiter dish biofilm formation assay is one of the most important methods of studying biofilm formation. In this study, the assay has been improvised to allow easy detection of biofilm formation on different substrata. The method has then been used to study growth conditions that affect biofilm formation, viz., the effect of pH, temperature, shaking conditions, and the carbon source provided. Glass, cellulose acetate, and carbon cloth materials were used as substrata to study biofilm development under the above conditions. The method was then extended to determine biofilm formation on the anodes of a microbial fuel cell in order to study the effect of biofilm formation on power production. A high correlation was observed between biofilm formation and power density (r = 0.951). When the electrode containing a biofilm was replaced with another electrode without biofilm, the average power density dropped from 59.55 to 5.76 mW/m2. This method offers an easy way to study the suitability of different materials to support biofilm formation. Growth conditions determining biofilm formation can be studied using this method. This method also offers a non-invasive way to determine biofilm formation on anodes of microbial fuel cells and preserves the anode for further studies.

Antibiotics Enhance Prevention and Eradication Efficacy of Cathodic-Voltage-Controlled Electrical Stimulation against Titanium-Associated Methicillin-Resistant Staphylococcus aureus and Pseudomonas aeruginosa Biofilms

Periprosthetic joint infections (PJIs) develop clinically in the presence of antibiotic therapies and are responsible for increased patient morbidity and rising health care costs. Many of these infections involve bacterial biofilm formation on orthopedic hardware, and it has been well established that these biofilms are refractory to most antibiotic treatments. Recent studies have focused on novel methods to prevent and eradicate infection. Cathodic-voltage-controlled electrical stimulation (CVCES) has previously been shown to be effective as a method for prevention and eradication of Gram-positive and Gram-negative infections. The present study revealed that the utility of CVCES for prevention and eradication of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa is enhanced in the presence of clinically relevant antibiotics. The synergistic effects of CVCES and antibiotics are effective in a magnitude-dependent manner. The results of this study indicate a promising alternative method to current PJI mitigation techniques.

Periprosthetic joint infection (PJI) develops clinically, even with antibiotic treatment, and methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa are predominant causes of these infections. Due to biofilm formation, antibiotic treatment for patients with PJI can perpetuate resistance, further complicating the use of noninvasive treatments. This study evaluated cathodic-voltage-controlled electrical stimulation (CVCES) of titanium, in combination with a clinically relevant antibiotic, to synergistically prevent MRSA and P. aeruginosa PJIs by inhibiting bacterial adherence or as a treatment for eradicating established biofilms. CVCES of −1.0 V, −1.5 V, or −1.8 V (versus Ag/AgCl), with or without vancomycin for MRSA or gentamicin for P. aeruginosa, was applied to sterile titanium incubated with cultures to evaluate prevention of attachment or eradication of preestablished biofilms. Treatments were 24 h long and included open-circuit potential controls, antibiotic alone, CVCES, and CVCES plus antibiotic. Biofilm-associated and planktonic CFU were enumerated. In general, CVCES at −1.8 V alone or with antibiotic completely eradicated biofilm-associated CFU for both strains, and these parameters were also highly effective against planktonic bacteria, resulting in a >6-log reduction in MRSA and no detectable planktonic P. aeruginosa. All CFU were reduced ∼3 to 5 logs from controls for prevention CVCES plus antibiotics at −1.0 V and −1.5 V against MRSA. Remarkably, there were no detectable P. aeruginosa CFU following prevention CVCES at −1.0 V or −1.5 V with gentamicin. Our results suggest that CVCES in combination with antibiotics may be an effective approach for prevention and treatment of PJI.

IMPORTANCE Periprosthetic joint infections (PJIs) develop clinically in the presence of antibiotic therapies and are responsible for increased patient morbidity and rising health care costs. Many of these infections involve bacterial biofilm formation on orthopedic hardware, and it has been well established that these biofilms are refractory to most antibiotic treatments. Recent studies have focused on novel methods to prevent and eradicate infection. Cathodic-voltage-controlled electrical stimulation (CVCES) has previously been shown to be effective as a method for prevention and eradication of Gram-positive and Gram-negative infections. The present study revealed that the utility of CVCES for prevention and eradication of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa is enhanced in the presence of clinically relevant antibiotics. The synergistic effects of CVCES and antibiotics are effective in a magnitude-dependent manner. The results of this study indicate a promising alternative method to current PJI mitigation techniques.

Disposable Patterned Electroceutical Dressing (PED-10) Is Safe for Treatment of Open Clinical Chronic Wounds

Objective: To evaluate if patterned electroceutical dressing (PED) is safe for human chronic wounds treatment as reported by wound care providers. Approach: This work reports a pilot feasibility study with the primary objective to determine physically observable effects of PED application on host tissue response from a safety evaluation point of view. For this pilot study, patients receiving a lower extremity amputation with at least one open wound on the part to be amputated were enrolled. Patients were identified through the Ohio State University Wexner Medical Center (OSUWMC) based on inclusion and exclusion criteria through prescreening through the Comprehensive Wound Center's (CWC) Limb Preservation Program and wound physicians and/or providers at OSUWMC. Wounds were treated with the PED before amputation surgery. Results: The intent of the study was to identify if PED was safe for clinical application based on visual observations of adverse or lack of adverse events on skin and wound tissue. The pilot testing performed on a small cohort (N = 8) of patients showed that with engineered voltage regulation of current flow to the open wound, the PED can be used with little to no visually observable adverse effects on chronic human skin wounds. Innovation: The PED was developed as a second-generation tunable electroceutical wound care dressing, which could potentially be used to treat wounds with deeper infections compared with current state of the art that treats wounds with treatment zone limited to the surface near topical application. Conclusion: Technology advances in design and fabrication of electroceutical dressings were leveraged to develop a tunable laboratory prototype that could be used as a disposable low-cost electroceutical wound care dressing on chronic wounds. Design revisions of PED-1 (1 kΩ ballast resistor) circumvented previously observed adverse effects on the skin in the vicinity of an open wound. PED-10 (including a 10 kΩ ballast resistor) was well tolerated in the small cohort of patients (N = 8) on whom it was tested, and the observations reported here warrant a larger study to determine the clinical impact on human wound healing and infection control.

Activity of fixed direct electrical current in experimental Staphylococcus aureus foreign-body osteomyelitis

Fixed DC was compared to ceftriaxone, ceftriaxone with 200 μA fixed DC, or no treatment in a rat model of methicillin-susceptible Staphylococcus aureus foreign-body osteomyelitis. After 3 weeks, fewer bacteria were present in bones of the ceftriaxone group (5.71 log₁₀cfu/g [P = 0.0004]) and the ceftriaxone/DC group (3.53 log₁₀cfu/g [P = 0.0002]) than untreated controls (6.70 log₁₀cfu/g). Fewer bacteria were present in the ceftriaxone/DC group than in the ceftriaxone-alone and DC-alone groups (P = 0.0012 and 0.0008, respectively). There were also fewer bacteria on the implanted wires in the groups treated with ceftriaxone (5.47 log₁₀cfu/cm²) or ceftriaxone/DC (2.82 log₁₀cfu/cm²) than in the untreated controls (6.44 log₁₀cfu/cm² [P = 0.0003 and 0.0002, respectively]). There were fewer bacteria in the ceftriaxone/DC rats than in the ceftriaxone-alone- and fixed DC-alone-treated rats (P = 0.0017 and 0.0016, respectively). Fixed DC with an antibiotic may be useful for treating foreign-body infections caused by S. aureus.

Total Eradication of Bacterial Infection in Root Canal Treatment: An Electrochemical Approach

According to the American Association of Endodontists, currently 22.3 million endodontic procedures are being performed annually with the success rate of 70-95% and the average survival rate of the root canal procedure is approximately 67% after 5 years and 56% after 8 years. One of the major reason for the failure is relapse of infection. Hence, it is imperative to develop an assistive or alternative method to eradicate the bacterial infection effectively without affecting patient compliance. The application of electrochemistry has been used previously to disinfect catheters and implant disinfection. Hence, the aim of this study is to utilize the principles of electrochemistry to develop a microelectronic device to eradicate bacterial infection for root canal treatment. The electrochemical protocol includes open circuit potential (60 s) and potentiostatic scan at varying voltage (-9 to +2 V) at a different time duration (1-5 min). Enterococcus faecalis in the form of planktonic and biofilm was used in this study. After electrochemical treatment, the bacterial viability was evaluated using alamarBlue assay, colony forming units, confocal microscopy, and scanning electron microscopy. Cytotoxicity evoked by electrochemical voltage in comparison to NaOCl solution was performed using osteoblasts in 2D and 3D cell culture systems. The results of the study show that the application of -2 to +2 V at 1-5 min did not show any significant reduction in bacterial growth. However, the cathodic voltage of -9 V for 5 min showed a significant reduction (p < 0.001) in the bacterial count (80-95%). Similar results were obtained from biofilm study, which is more realistic to the in vivo condition. In contrast, the method did not induce cytotoxicity to the cells in 3D culture system (65% viability) in comparison to the highly toxic nature (0% viability) of NaOCl, indicating better patient compliance. Hence, the study provides supporting evidence to develop an electrochemically driven microelectronic device that can be a potential assistive dental instrument for endodontic procedures.

Impact of bacterial streamers on biofouling of microfluidic filtration systems

We investigate the effect of biofouling in a microfluidic filtration system. The microfluidic platform consists of cylindrical microposts with a pore-spacing of 2 μm, which act as the filtration section of the device. One of our key findings is that there exists a critical pressure difference above which pronounced streamer formation is observed, which eventually leads to rapid clogging of the device with an accompanying exponential decrease in permeate flow. Moreover, when streamers do form, de-clogging of pores also occurs intermittently, which leads to small time scale fluctuations [O(10¹ s)] superimposed upon the large time scale [O(10² min)] clogging of the system. These de-clogging phenomena lead to a sharp increase in water permeation through the microfluidic filtration device but rates the water quality as biomass debris is transported in the permeate. Streamer-based clogging shares similarities with various fouling mechanisms typically associated with membranes. Finally, we also show that the pH of the feed strongly affects biofouling of the microfluidic filtration system.

Application of bioelectric effect to reduce the antibiotic resistance of subgingival plaque biofilm: An in vitro study

Context:

Biofilms are known for their antimicrobial resistance, and so is the subgingival plaque biofilm, the primary etiologic factor for periodontal infections.

Aims:

The objective of this study is to investigate if the subgingival plaque biofilm resistance can be reduced using doxycycline in the presence of low-intensity electric field (bioelectric effect).

Settings and Design:

The study was an in vitro microbiological study.

Materials and Methods:

Subgingival plaque samples from chronic periodontitis patients were collected to grow subgingival plaque biofilms on hydroxyapatite disks. Hydroxyapatite disks with the plaque biofilms from each patient were divided into four groups: (i) No intervention – control, (ii) current alone – CU; (iii) doxycycline – AB, and (iv) combined treatment – CU + AB. After respective treatments, the disks were anaerobically incubated for 48 h, the biofilm was dispersed and subcultured and colony-forming unit/mL was estimated in all the four groups.

Statistical Analysis:

Statistical analysis was done using Mann–Whitney and Kruskal–Wallis tests for intergroup comparisons. T-test was done to assess the difference in current flow between the groups CU and CU + AB.

Results:

All the three treatment modalities showed antibacterial effect. Application of current alone resulted in reduced bacterial growth than control group. Doxycycline alone resulted in reduction in bacterial counts better than control and current alone groups. The combination treatment showed greatest inhibition of bacterial colonies.

Conclusion:

The ability of doxycycline antibiotic in inhibiting plaque biofilm was significantly enhanced by application of a weak electric field (5 volts for 2 min).

Cold Plasmas for Biofilm Control: Opportunities and Challenges

Bacterial biofilm infections account for a major proportion of chronic and medical device associated infections in humans, yet our ability to control them is compromised by their inherent tolerance to antimicrobial agents. Cold atmospheric plasma (CAP) represents a promising therapeutic option. CAP treatment of microbial biofilms represents the convergence of two complex phenomena: the production of a chemically diverse mixture of reactive species and intermediates, and their interaction with a heterogeneous 3D interface created by the biofilm extracellular polymeric matrix. Therefore, understanding these interactions and physiological responses to CAP exposure are central to effective management of infectious biofilms. We review the unique opportunities and challenges for translating CAP to the management of biofilms.

Natural and bioinspired nanostructured bactericidal surfaces

Bacterial antibiotic resistance is becoming more widespread due to excessive use of antibiotics in healthcare and agriculture. At the same time the development of new antibiotics has effectively ground to a hold. Chemical modifications of material surfaces have poor long-term performance in preventing bacterial build-up and hence approaches for realising bactericidal action through physical surface topography have become increasingly important in recent years. The complex nature of the bacteria cell wall interactions with nanostructured surfaces represents many challenges while the design of nanostructured bactericidal surfaces is considered. Here we present a brief overview of the bactericidal behaviour of naturally occurring and bio-inspired nanostructured surfaces against different bacteria through the physico-mechanical rupture of the cell wall. Many parameters affect this process including the size, shape, density, rigidity/flexibility and surface chemistry of the surface nanotextures as well as factors such as bacteria specificity (e.g. gram positive and gram negative) and motility. Different fabrication methods for such bactericidal nanostructured surfaces are summarised.

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

Bacterial biofilms are the primary cause of infections in medical implants and catheters. Delayed detection of biofilm infections contributes to the widespread use of high doses of antibiotics, leading to the emergence of antibiotic-resistant bacterial strains. Accordingly, there is an urgent need for systems that can rapidly detect and treat biofilm infections in situ. As a step toward this goal, in this work we have developed for the first time a threshold-activated feedback-based impedance sensor-treatment system for combined real-time detection and treatment of biofilms. Specifically, we demonstrate the use of impedimetric sensing to accurately monitor the growth of Escherichia coli biofilms in microfluidic flow cells by measuring the fractional relative change (FRC) in absolute impedance. Furthermore, we demonstrate the use of growth measurements as a threshold-activated trigger mechanism to initiate successful treatment of biofilms using bioelectric effect (BE), applied through the same sensing electrode array. This was made possible through a custom program that (a) monitored the growth and removal of biofilms within the microfluidic channels in real-time and (b) enabled the threshold-based activation of BE treatment. Such BE treatment resulted in a ∼74.8 % reduction in average biofilm surface coverage as compared to the untreated negative control. We believe that this smart microsystem for integrated biofilm sensing and treatment will enable future development of autonomous biosensors optimized for accurate real-time detection of the onset of biofilms and their in situ treatment, directly on the surfaces of medical implants.

Autoinducer-2 analogs and electric fields - an antibiotic-free bacterial biofilm combination treatment

Bacterial biofilms are a common cause of chronic medical implant infections. Treatment and eradication of biofilms by conventional antibiotic therapy has major drawbacks including toxicity and side effects associated with high-dosage antibiotics. Additionally, administration of high doses of antibiotics may facilitate the emergence of antibiotic resistant bacteria. Thus, there is an urgent need for the development of treatments that are not based on conventional antibiotic therapies. Presented herein is a novel bacterial biofilm combination treatment independent of traditional antibiotics, by using low electric fields in combination with small molecule inhibitors of bacterial quorum sensing - autoinducer-2 analogs. We investigate the effect of this treatment on mature Escherichia coli biofilms by application of an alternating and offset electric potential in combination with the small molecule inhibitor for 24 h using both macro and micro-scale devices. Crystal violet staining of the macro-scale biofilms shows a 46 % decrease in biomass compared to the untreated control. We demonstrate enhanced treatment efficacy of the combination therapy using a high-throughput polydimethylsiloxane-based microfluidic biofilm analysis platform. This microfluidic flow cell is designed to reduce the growth variance of in vitro biofilms while providing an integrated control, and thus allows for a more reliable comparison and evaluation of new biofilm treatments on a single device. We utilize linear array charge-coupled devices to perform real-time tracking of biomass by monitoring changes in optical density. End-point confocal microscopy measurements of biofilms treated with the autoinducer analog and electric fields in the microfluidic device show a 78 % decrease in average biofilm thickness in comparison to the negative controls and demonstrate good correlation with real-time optical density measurements. Additionally, the combination treatment showed 76 % better treatment efficacy compared to conventional antibiotic therapy. Taken together these results suggest that the antibiotic-free combination treatment described here may provide an effective alternative to traditional antibiotic therapies against bacterial biofilm infections. Use of this combination treatment in the medical and environmental fields would alleviate side effects associated with high-dosage antibiotic therapies, and reduce the rise of antibiotic-resistant bacteria.

Microfluidic accumulation assay probes attachment of biofilm forming diatom cells

Testing of fouling release (FR) technologies is of great relevance for discovery of the next generation of protective marine coatings. In this paper, an accumulation assay to test diatom interaction under laminar flow with the model organism Navicula perminuta is introduced. Using time lapse microscopy with large area sampling allows determination of the accumulation kinetics of the diatom on three model surfaces with different surface properties at different wall shear stresses. The hydrodynamic conditions within the flow cell are described and a suitable shear stress range to perform accumulation experiments is identified at which statistically significant discrimination of surfaces is possible. The observed trends compare well to published adhesion preferences of N. perminuta. Also, previously determined trends of critical wall shear stresses required for cell removal from the same set of functionalized interfaces shows consistent trends. Initial attachment mediated by extracellular polymeric substances (EPS) present outside the diatoms leads to the conclusion that the FR potential of the tested coating candidates can be deducted from dynamic accumulation experiments under well-defined hydrodynamic conditions. As well as testing new coating candidates for their FR properties, monitoring of the adhesion process under flow provides additional information on the mechanism and geometry of attachment and the population kinetics.

Eradication of Pseudomonas aeruginosa cells by cathodic electrochemical currents delivered with graphite electrodes

Antibiotic resistance is a major challenge to the treatment of bacterial infections associated with medical devices and biomaterials. One important intrinsic mechanism of such resistance is the formation of persister cells that are phenotypic variants of microorganisms and highly tolerant to antibiotics. Recently, we reported a new approach to eradicating persister cells of Pseudomonas aeruginosa using low-level direct electrochemical current (DC) and synergy with the antibiotic tobramycin. To further understand the underlying mechanism and develop this technology toward possible medical applications, we investigated the electricidal activities of non-metallic biomaterial on persister and biofilm cells of P. aeruginosa using graphite-based TGON™ 805 electrodes. We employed both single and dual chamber systems to compare electrochemical factors of TGON and stainless steel 304 electrodes. The results revealed that TGON-based treatments were highly effective against P. aeruginosa persister cells. In the single chamber system, complete eradication of planktonic persister cells (corresponding to a 7-log killing) was achieved with 70μA/cm² DC using TGON electrodes within 40min of treatment, while the cell viability in biofilms was reduced by 2 logs within 1h. The killing effects were dose and time dependent with higher current densities requiring less time. Moreover, reduction reactions were found more effective than oxidation reactions, confirming that metal cations are not indispensable, although they may facilitate cell killing. The findings of this study can help develop electrochemical technologies to eradicate persister and biofilm cells for more effective treatment of medical device and biomaterial associated infections.

STATEMENT OF SIGNIFICANCE

Infections associated with medical devices and biomaterials present a major challenge due to high-level tolerance of microbes to conventional antibiotics. It is well established that such tolerance is due to the formation of dormant persister cells and multicellular structures known as biofilms. Recent studies have demonstrated electrochemical treatment as a promising alternative to eradicate bacterial infections, since the killing mechanism is independent of the growth phase of bacterial cells, but relies on various electrochemical species interplaying during the treatment. The current study investigated major bactericidal properties of the electrochemical currents mediated via TGON, a carbon-based electrode material. Up to total eradication of Pseudomonas aeruginosa persister cells was achieved. The new knowledge of electrochemical properties and the bioactivity of TGON may help develop new methods/devices to eradicate bacterial infections by delivering safe levels of electrochemical currents.

Cutaneous wound biofilm and the potential for electrical stimulation in management of the microbiome

Infection contributes significantly to delayed cutaneous wound healing, which impacts patient care. External application of electrical stimulation (ES) has beneficial effects on wound repair and regeneration. The majority of studies to date have explored ES in relation to planktonic microorganisms, yet evidence indicates that bacteria in chronic wounds reside as antibiotic-resistant polymicrobial biofilms, which contribute to impairing wound healing. Culture-independent sequencing techniques have revolutionized our understanding of the skin microbiome and allowed a more accurate determination of microbial taxa and their relative abundance in wounds allowing a greater understanding of the host–microbial interface. Future studies combining the fields of ES, biofilm and microbiome research are necessary to fully elucidate the use of ES in the management of wound infection.

Hydrodynamic Effects on Biofilms at the Biointerface Using a Microfluidic Electrochemical Cell: Case Study of Pseudomonas sp

The anchoring biofilm layer is expected to exhibit a different response to environmental stresses than for portions in the bulk, due to the protection from other strata and the proximity to the attachment surface. The effect of hydrodynamic stress on surface-adhered biofilm layers was tested using a specially designed microfluidic bio flow cell with an embedded three-electrode detection system. In situ electrochemical impedance spectroscopy (EIS) measurements of biocapacitance and bioresistance of Pseudomonas sp. biofilms were conducted during the growth phase and under different shear flow conditions with verification by other surface sensitive techniques. Distinct, but reversible changes to the amount of biofilm and its structure at the attachment surface were observed during the application of elevated shear stress. In contrast, regular microscopy revealed permanent distortion to the biofilm bulk, in the form of streamers and ripples. Following the application of extreme shear stresses, complete removal of significant portions of biofilm outer layers occurred, but this did not change the measured quantity of biofilm at the electrode attachment surface. The structure of the remaining biofilm, however, appeared to be modified and susceptible to further changes following application of shear stress directly to the unprotected biofilm layers at the attachment surface.

Cathodic voltage-controlled electrical stimulation of titanium for prevention of methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii biofilm infections

Antibiotic resistance of bacterial biofilms limits available treatment methods for implant-associated orthopaedic infections. This study evaluated the effects of applying cathodic voltage-controlled electrical stimulations (CVCES) of -1.5V and -1.8V (vs. Ag/AgCl) to coupons of commercially pure titanium (cpTi) incubated in cultures of methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii (A. baumannii) as a method of preventing bacterial attachment. Stimulations were applied for 2, 4, and 8h and coupon-associated and planktonic colony-forming units (CFU) were enumerated following stimulation. Compared to open circuit potential (OCP) controls, CVCES for 4h at -1.8V significantly reduced coupon-associated MRSA CFU by 99.9% (1.30×10⁴vs. 4.45×10⁷, p=0.047) and A. baumannii coupon-associated CFU by 99.9% (1.64×10⁴vs. 5.93×10⁷, p=0.001) and reduced planktonic CFU below detectable levels for both strains. CVCES at -1.8V for 8h also reduced coupon-associated and planktonic CFU below detectable levels for each strain. CVCES at -1.5V for 4 and 8h, and -1.8V for 2h did not result in clinically relevant reductions. For 4 and 8h stimulations, the current density was significantly higher for -1.8V than -1.5V, an effect directly related to the rate of water and oxygen reduction on the cpTi surface. This significantly increased the pH, a suspected influence in decreased CFU viability. The voltage-dependent electrochemical properties of cpTi likely contribute to the observed antimicrobial effects of CVCES. This study revealed that CVCES of titanium could prevent coupon-associated and planktonic CFU of Gram-positive MRSA and Gram-negative A. baumannii from reaching detectable levels in a magnitude-dependent and time-dependent manner.

STATEMENT OF SIGNIFICANCE

Periprosthetic joint infection is a devastating outcome of total joint arthroplasty and has led to increased patient morbidity and rising healthcare costs. Current treatments are limited by the growing prevalence of antimicrobial resistant biofilms. Therefore, there is a growing interest in the prevention of bacterial colonization of implants. Previous work has shown that cathodic voltage-controlled electrical stimulation (CVCES) of titanium is effective both in vitro and in vivo as an antimicrobial strategy to eradicate established implant-associated biofilm infections. The present study revealed that CVCES of titanium coupons also has utility in preventing coupon-associated and planktonic colony-forming units of Gram-positive methicillin-resistant Staphylococcus aureus and Gram-negative Acinetobacter baumannii from reaching detectable levels in a magnitude-dependent and time-dependent manner.

Influence of low direct electric currents and chlorhexidine upon human dental biofilms

Dental biofilms have been widely associated with biological complications of oral implants. Currently, no consensus exists regarding the most reliable anti-infective approach to treat peri-implantitis. This study aimed to investigate whether low direct electric currents (DC) could influence chlorhexidine (CHX) 0.2% antimicrobial efficacy against human dental biofilms. To support biofilm accumulation, discs made with machined titanium (Ti) or hydroxyapatite (HA) were used. Five volunteers wore during 24 h an intraoral thermoformed splint on which ten specimens were bonded. Biofilms were then collected and treated ex vivo. During each antimicrobial experiment (N = 20 replicates), two modalities of treatment (CHX/PBS = control groups and CHX/PBS+5mA = test groups) were tested (n = 5 discs each) and the number of viable bacteria evaluated in LogCFU/mL at baseline, 0.5, 1, 2 and 5 min. The proportion of killed bacteria was also estimated and compared statistically at each time point between control and test groups. CHX+/-5mA induced a mean viability reduction around 90-95% after 5 min of treatment whatever the surface considered (Ti/HA). A significant difference regarding the bactericidal effect was noted on Ti surfaces after 0.5, 1 and 2 min in favor of the CHX+5mA modality when compared to CHX alone (p < 0.05). PBS+5mA also had a certain antimicrobial effect (58%) after 5 min on Ti surfaces. This effect was significantly higher than that observed with PBS (25%) (p < 0.05). This study showed that low DC (5mA) can have an antibiofilm effect and are also able to enhance chlorhexidine 0.2% efficacy against human dental biofilms grown on titanium surfaces.

Role of duty cycle on Pseudomonas aeruginosa growth inhibition mechanisms by positive electric pulses

BACKGROUND

P. aeruginosa considered as a notoriously difficult organism to be controlled by antibiotics or disinfectants. The potential use of alternative means as an aid to avoid the wide use of antibiotics against bacteria pathogen has been recently arisen remarkably.

OBJECTIVE

Effect of extremely low frequency positive electric pulse with different duty cycles on Pseudomonas aeruginosa (ATCC: 27853) growth by constructed and implemented exposure device was investigated in this study.

METHODS

The exposure device was applied to give extremely low frequency in the range of 0.1 up to 20 Hz with the capability to control the duty cycle of each pulse with variation from 10% up to 100%. Growth curves of Pseudomonas aeruginosa were investigated before and after exposure to different frequencies (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 Hz) through measuring the optical density and cell count. Exposures to selected frequencies in the whole ranges of duty cycles were done. These studies were followed by DNA fragmentation, transmission electron microscope (TEM), antibiotic susceptibility tests, and dielectric measurements.

RESULTS

Findings revealed inhibition effect by 48.56% and 47.4% together with change in the DNA structural properties for samples exposed to 0.5 Hz and 0.7 Hz respectively. Moreover the data indicated important role of duty cycle on the inhibition mechanism.

CONCLUSION

It is concluded that there are two different mechanisms of interaction between positive electric pulse and microorganism occurred; 0.5 Hz caused rupture in cell wall while 0.7 Hz caused denaturation of the inner consistent of the cell.

Effect of electrical energy on the efficacy of biofilm treatment using the bioelectric effect

Background/Objectives:

The use of electric fields in combination with small doses of antibiotics for enhanced treatment of biofilms is termed the ‘bioelectric effect’ (BE). Different mechanisms of action for the AC and DC fields have been reported in the literature over the last two decades. In this work, we conduct the first study on the correlation between the electrical energy and the treatment efficacy of the bioelectric effect on Escherichia coli K-12 W3110 biofilms.

Methods:

A thorough study was performed through the application of alternating (AC), direct (DC) and superimposed (SP) potentials of different amplitudes on mature E. coli biofilms. The electric fields were applied in combination with the antibiotic gentamicin (10 μg/ml) over a course of 24 h, after the biofilms had matured for 24 h. The biofilms were analysed using the crystal violet assay, the colony-forming unit method and fluorescence microscopy.

Results:

Results show that there is no statistical difference in treatment efficacy between the DC-, AC- and SP-based BE treatment of equivalent energies (analysis of variance (ANOVA) P>0.05) for voltages <1 V. We also demonstrate that the efficacy of the BE treatment as measured by the crystal violet staining method and colony-forming unit assay is proportional to the electrical energy applied (ANOVA P<0.05). We further verify that the treatment efficacy varies linearly with the energy of the BE treatment (r²=0.984). Our results thus suggest that the energy of the electrical signal is the primary factor in determining the efficacy of the BE treatment, at potentials less than the media electrolysis voltage.

Conclusions:

Our results demonstrate that the energy of the electrical signal, and not the type of electrical signal (AC or DC or SP), is the key to determine the efficacy of the BE treatment. We anticipate that this observation will pave the way for further understanding of the mechanism of action of the BE treatment method and may open new doors to the use of electric fields in the treatment of bacterial biofilms.

Atmospheric pressure nonthermal plasmas for bacterial biofilm prevention and eradication

Biofilms are three-dimensional structures formed by surface-attached microorganisms and their extracellular products. Biofilms formed by pathogenic microorganisms play an important role in human diseases. Higher resistance to antimicrobial agents and changes in microbial physiology make treating biofilm infections very complex. Atmospheric pressure nonthermal plasmas (NTPs) are a novel and powerful tool for antimicrobial treatment. The microbicidal activity of NTPs has an unspecific character due to the synergetic actions of bioactive components of the plasma torch, including charged particles, reactive species, and UV radiation. This review focuses on specific traits of biofilms, their role in human diseases, and those effects of NTP that are helpful for treating biofilm infections. The authors discuss NTP-based strategies for biofilm control, such as surface modifications to prevent bacterial adhesion, killing bacteria in biofilms, and biofilm destruction with NTPs. The unspecific character of microbicidal activity, proven polymer modification and destruction abilities, low toxicity for human tissues and absence of long-living toxic compounds make NTPs a very promising tool for biofilm prevention and control.

Targeted release of tobramycin from a pH-responsive grafted bilayer challenged with S. aureus

A stimuli-responsive, controlled release bilayer for the prevention of bacterial infection on biomaterials is presented. Drug release is locally controlled by the pH-responsiveness of the bilayer, comprised of an inner poly(acrylic acid) (PAA) monolayer grafted to a biomaterial and cross-linked with an outer chitosan (CH) brush. Tobramycin (TOB) is loaded in the inner PAA in part to minimize bacteria resistance. Because biofilm formation causes a decrease in local pH, TOB is released from PAA and permeates through the CH, which is in contact with the biofilm. Antibiotic capacity is controlled by the PAA thickness, which depends on PAA brush length and the extent of cross-linking between CH and PAA at the bilayer interface. This TOB-loaded, pH-responsive bilayer exhibits significantly enhanced antibacterial activity relative to controls.

Cathodic voltage-controlled electrical stimulation of titanium implants as treatment for methicillin-resistant Staphylococcus aureus periprosthetic infections

Effective treatment options are often limited for implant-associated orthopedic infections. In this study we evaluated the antimicrobial effects of applying cathodic voltage-controlled electrical stimulation (CVCES) of -1.8 V (vs. Ag/AgCl) to commercially pure titanium (cpTi) substrates with preformed biofilm-like structures of methicillin-resistant Staphylococcus aureus (MRSA). The in vitro studies showed that as compared to the open circuit potential (OCP) conditions, CVCES of -1.8 V for 1 h significantly reduced the colony-forming units (CFU) of MRSA enumerated from the cpTi by 97% (1.89 × 106 vs 6.45 × 104 CFU/ml) and from the surrounding solution by 92% (6.63 × 105 vs. 5.15 × 104 CFU/ml). The in vivo studies, utilizing a rodent periprosthetic infection model, showed that as compared to the OCP conditions, CVCES at -1.8 V for 1 h significantly reduced MRSA CFUs in the bone tissue by 87% (1.15 × 105 vs. 1.48 × 104 CFU/ml) and reduced CFU on the cpTi implant by 98% (5.48 × 104 vs 1.16 × 103 CFU/ml). The stimulation was not associated with histological changes in the host tissue surrounding the implant. As compared to the OCP conditions, the -1.8 V stimulation significantly increased the interfacial capacitance (18.93 vs. 98.25 μF/cm(2)) and decreased polarization resistance (868,250 vs. 108 Ω-cm(2)) of the cpTi. The antimicrobial effects are thought to be associated with these voltage-dependent electrochemical surface properties of the cpTi.

Prevention and treatment of biofilms by hybrid- and nanotechnologies

Bacteria growing as adherent biofilms are difficult to treat and frequently develop resistance to antimicrobial agents. To counter biofilms, various approaches, including prevention of bacterial surface adherence, application of device applicators, and assimilation of antimicrobials in targeted drug delivery machinery, have been utilized. These methods are also combined to achieve synergistic bacterial killing. This review discusses various multimodal technologies, presents general concepts, and describes therapies relying on the principles of electrical energy, ultrasound, photodynamics, and targeted drug delivery for prevention and treatment of biofilms.

A flat microbial fuel cell for decentralized wastewater valorization: process performance and optimization potential

A very compact flat microbial fuel cell (MFC), with 64 cm2 each for the anode surface and the cathode surface and 1 cm3 each for the anode and cathode chambers, was tested for wastewater treatment with simultaneous electricity production with the ultimate goal of implementing an autonomous service in decentralized wastewater treatment systems. The MFC was operated with municipal wastewater in sequencing batch reactor mode with re-circulation. Current densities up to 407 W/m3 and a carbon removal of 83% were obtained. Interruption in the operation slightly decreased power density, while the re-circulation ratio did not influence power generation. The anode biofilm presented high conductivity, activity and diversity. The denaturing gradient gel electrophoresis band-pattern of the DNA showed the presence of several ribotypes with different species of Shewanellaceae and Geobacteraceae families.

Molar mass, entanglement, and associations of the biofilm polysaccharide of Staphylococcus epidermidis

Biofilms are microbial communities that are characterized by the presence of a viscoelastic extracellular polymeric substance (EPS). Studies have shown that polysaccharides, along with proteins and DNA, are a major constituent of the EPS and play a dominant role in mediating its microstructure and rheological properties. Here, we investigate the possibility of entanglements and associative complexes in solutions of extracellular polysaccharide intercellular adhesin (PIA) extracted from Staphylococcus epidermidis biofilms. We report that the weight average molar mass and radius of gyration of PIA isolates are 2.01×10(5)±1200 g/mol and 29.2±1.2 nm, respectively. The coil overlap concentration, c*, was thus determined to be (32±4)×10(-4) g/mL. Measurements of the in situ concentration of PIA (cPIA,biofilm) was found to be (10±2)×10(-4) g/mL.Thus, cPIA,biofilm Collapse

Key Words

• staphylococcus epidermidis
• biofilm
• entangled polymers
• polysaccharide-protein complex
• extracellular polysaccharides
• static light scattering

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MESH Headings

• Animals
• Bacterial Adhesion
• Biofilms/growth & development
• Carbohydrate Conformation
• Cattle
• Elasticity
• Hydrogen Bonding
• Hydrogen-Ion Concentration
• Polysaccharides, Bacterial/chemistry
• Polysaccharides, Bacterial/isolation & purification
• Protein Binding
• Serum Albumin, Bovine/chemistry
• Staphylococcus epidermidis/chemistry
• Static Electricity
• Viscosity

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Grants

• R01 GM069438 NIGMS NIH HHS
• R01 GM081702 NIGMS NIH HHS
• GM-069438 NIGMS NIH HHS

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Affiliation(s)

Mahesh Ganesan Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105
Elizabeth J. Stewart Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105
Jacob Szafranski Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
Ashley Satorius Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
John G. Younger Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48105
Michael J. Solomon Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48105

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On the mechanics of bacterial biofilms on non-dissolvable surgical sutures: a laser scanning confocal microscopy-based finite element study

Biofilms are bacterial communities encapsulated within a self-secreted extracellular polymeric substance and are responsible for a wide range of chronic medical device related infections. Understanding and addressing the conditions that lead to the attachment and detachment of biofilms from biomedical surfaces (orthopaedic implants, sutures, intravenous catheters, cardio-vascular stents) has the potential to identify areas of the device that might be more prone to infection and predict how and when biofilms might dislodge. In this study, an integrated software methodology was devised to create image-based microscopic finite element models of real biofilm colonies of Staphylococcus aureus attached to a fragment of surgical suture. The goal was to predict how deformation of the suture may lead to the potential detachment of biofilm colonies by solving the equations of continuum mechanics using the finite element method for various loading cases. Tension, torsion and bending of the biomaterial structure were simulated, demonstrating that small strains in the suture can produce surface shear stresses sufficient to trigger the sliding of biofilms over the suture surface. Applications of this technique to other medical devices are discussed.

Direct electric current treatment under physiologic saline conditions kills Staphylococcus epidermidis biofilms via electrolytic generation of hypochlorous acid

The purpose of this study was to investigate the mechanism by which a direct electrical current reduced the viability of Staphylococcus epidermidis biofilms in conjunction with ciprofloxacin at physiologic saline conditions meant to approximate those in an infected artificial joint. Biofilms grown in CDC biofilm reactors were exposed to current for 24 hours in 1/10^th strength tryptic soy broth containing 9 g/L total NaCl. Dose-dependent log reductions up to 6.7 log₁₀ CFU/cm² were observed with the application of direct current at all four levels (0.7 to 1.8 mA/cm²) both in the presence and absence of ciprofloxacin. There were no significant differences in log reductions for wells with ciprofloxacin compared to those without at the same current levels. When current exposures were repeated without biofilm or organics in the medium, significant generation of free chlorine was measured. Free chlorine doses equivalent to the 24 hour endpoint concentration for each current level were shown to mimic killing achieved by current application. Current exposure (1.8 mA/cm²) in medium lacking chloride and amended with sulfate, nitrate, or phosphate as alternative electrolytes produced diminished kills of 3, 2, and 0 log reduction, respectively. Direct current also killed Pseudomonas aeruginosa biofilms when NaCl was present. Together these results indicate that electrolysis reactions generating hypochlorous acid from chloride are likely a main contributor to the efficacy of direct current application. A physiologically relevant NaCl concentration is thus a critical parameter in experimental design if direct current is to be investigated for in vivo medical applications.