Clinically applicable irreversible electroporation for eradication of micro-organisms

Inactivation of antibiotic-resistant bacteria Escherichia coli by electroporation

Introduction

In modern times, bacterial infections have become a growing problem in the medical community due to the emergence of antibiotic-resistant bacteria. In fact, the overuse and improper disposal of antibiotics have led to bacterial resistance and the presence of such bacteria in wastewater. Therefore, it is critical to develop effective strategies for dealing with antibiotic-resistant bacteria in wastewater. Electroporation has been found to be one of the most promising complementary techniques for bacterial inactivation because it is effective against a wide range of bacteria, is non-chemical and is highly optimizable. Many studies have demonstrated electroporation-assisted inactivation of bacteria, but rarely have clinical antibiotics or bacteria resistant to these antibiotics been used in the study. Therefore, the motivation for our study was to use a treatment regimen that combines antibiotics and electroporation to inactivate antibiotic-resistant bacteria.

Methods

We separately combined two antibiotics (tetracycline and chloramphenicol) to which the bacteria are resistant (with a different resistance mode) and electric pulses. We used three different concentrations of antibiotics (40, 80 and 150 µg/ml for tetracycline and 100, 500 and 2000 µg/ml for chloramphenicol, respectively) and four different electric field strengths (5, 10, 15 and 20 kV/cm) for electroporation.

Results and discussion

Our results show that electroporation effectively enhances the effect of antibiotics and inactivates antibiotic-resistant bacteria. The inactivation rate for tetracycline or chloramphenicol was found to be different and to increase with the strength of the pulsed electric field and/or the concentration of the antibiotic. In addition, we show that electroporation has a longer lasting effect (up to 24 hours), making bacteria vulnerable for a considerable time. The present work provides new insights into the use of electroporation to inactivate antibiotic-resistant bacteria in the aquatic environment.

Reduced Graphene Oxide-Coated Fabrics for Joule-Heating and Antibacterial Applications

Multifunctional textiles have emerged as a significant area of research due to their growing importance and diverse applications. The main requirement for these fabrics is electroconductivity, which is usually gained by incorporating conductive materials such as graphene into the textile structure. In this article, an electrochemical method was demonstrated to integrate different loadings of reduced graphene oxide (rGO) into fabrics for enhanced electrical conductivity. The process involves spray coating of graphene oxide (GO) onto the fabric, followed by in situ electrochemical reduction of GO, resulting in a coating layer of rGO nanosheets. The rGO-coated fabric exhibited exceptional Joule-heating capabilities, achieving 127 °C under a 9 V direct voltage with only 770 μg/cm2 of rGO loading. Moreover, the antibacterial properties of the rGO-coated fabric were demonstrated, showing a significant reduction rate of over 99.99% against both Bacillus subtilis and Escherichia coli. Joule-heating and antibacterial performances of the rGO-coated fabric were investigated over eight repeated cycles, demonstrating excellent repeatability. The simplicity of the fabrication method, along with the electrothermal and antibacterial effects of the rGO-coated fabric, makes it a promising material for various practical applications.

The bioelectrical properties of bone tissue

Understanding the bioelectrical properties of bone tissue is key to developing new treatment strategies for bone diseases and injuries, as well as improving the design and fabrication of scaffold implants for bone tissue engineering. The bioelectrical properties of bone tissue can be attributed to the interaction of its various cell lineages (osteocyte, osteoblast and osteoclast) with the surrounding extracellular matrix, in the presence of various biomechanical stimuli arising from routine physical activities; and is best described as a combination and overlap of dielectric, piezoelectric, pyroelectric and ferroelectric properties, together with streaming potential and electro-osmosis. There is close interdependence and interaction of the various electroactive and electrosensitive components of bone tissue, including cell membrane potential, voltage-gated ion channels, intracellular signaling pathways, and cell surface receptors, together with various matrix components such as collagen, hydroxyapatite, proteoglycans and glycosaminoglycans. It is the remarkably complex web of interactive cross-talk between the organic and non-organic components of bone that define its electrophysiological properties, which in turn exerts a profound influence on its metabolism, homeostasis and regeneration in health and disease. This has spurred increasing interest in application of electroactive scaffolds in bone tissue engineering, to recapitulate the natural electrophysiological microenvironment of healthy bone tissue to facilitate bone defect repair.

Electroactive Biomaterials for Facilitating Bone Defect Repair under Pathological Conditions

Bone degeneration associated with various diseases is increasing due to rapid aging, sedentary lifestyles, and unhealthy diets. Living bone tissue has bioelectric properties critical to bone remodeling, and bone degeneration under various pathological conditions results in significant changes to these bioelectric properties. There is growing interest in utilizing biomimetic electroactive biomaterials that recapitulate the natural electrophysiological microenvironment of healthy bone tissue to promote bone repair. This review first summarizes the etiology of degenerative bone conditions associated with various diseases such as type II diabetes, osteoporosis, periodontitis, osteoarthritis, rheumatoid arthritis, osteomyelitis, and metastatic osteolysis. Next, the diverse array of natural and synthetic electroactive biomaterials with therapeutic potential are discussed. Putative mechanistic pathways by which electroactive biomaterials can mitigate bone degeneration are critically examined, including the enhancement of osteogenesis and angiogenesis, suppression of inflammation and osteoclastogenesis, as well as their anti-bacterial effects. Finally, the limited research on utilization of electroactive biomaterials in the treatment of bone degeneration associated with the aforementioned diseases are examined. Previous studies have mostly focused on using electroactive biomaterials to treat bone traumatic injuries. It is hoped that this review will encourage more research efforts on the use of electroactive biomaterials for treating degenerative bone conditions.

Electroporation as an Efficacy Potentiator for Antibiotics With Different Target Sites

Antibiotic resistance is a global health threat, and there is ample motivation for development of novel antibacterial approaches combining multiple strategies. Electroporation is among the promising complementary techniques – highly optimizable, effective against a broad range of bacteria, and largely impervious to development of resistance. To date, most studies investigating electroporation as an efficacy potentiator for antibacterials used substances permissible in food industry, and only few used clinical antibiotics, as acceptable applications are largely limited to treatment of wastewaters inherently contaminated with such antibiotics. Moreover, most studies have focused mainly on maximal achievable effect, and less on underlying mechanisms. Here, we compare Escherichia coli inactivation potentiation rates for three antibiotics with different modes of action: ampicillin (inhibits cell wall synthesis), ciprofloxacin (inhibits DNA replication), and tetracycline (inhibits protein synthesis). We used concentrations for each antibiotic from 0 to 30× its minimum inhibitory concentration, a single 1-ms electric pulse with amplitude from 0 to 20 kV/cm, and post-pulse pre-dilution incubation either absent (≲1 min) or lasting 60 min, 160 min, or 24 h. Our data show that with incubation, potentiation is significant for all three antibiotics, increases consistently with pulse amplitude, and generally also with antibiotic concentration and incubation time. With incubation, potentiation for ampicillin was rather consistently (although with weak statistical significance) superior to both ciprofloxacin and tetracycline: ampicillin was superior to both in 42 of 48 data points, including 7 with significance with respect to both, while at 60- and 160-min incubation, it was superior in 31 of 32 data points, including 6 with significance with respect to both. This suggests that electroporation potentiates wall-targeting antibiotics more than those with intracellular targets, providing motivation for in-depth studies of the relationship between the mode of action of an antibiotic and its potentiation by electroporation. Identification of substances permissible in foods and targeting the cell wall of both Gram-negative and Gram-positive bacteria might provide candidate antibacterials for broad and strong potentiation by electroporation applicable also for food preservation.

Electrical Control of Escherichia coli Growth Measured with Simultaneous Modulation and Imaging

Background: The use of electricity to mediate bacterial growth is unique in providing spatial control, but requires a more detailed understanding. Methods: We use two gold wires on a glass coverslip with an overlayer of agar to image Escherichia coli cells with brightfield and fluorescence microscopy while simultaneously applying a voltage. Cells outside of the wires provide a control population to measure cell growth as a function of voltage, rather than any difference in culture conditions or growth phase. Results: An applied voltage suppresses the fraction of E. coli undergoing elongation and division with recovery to control values when the voltage is removed. Depolarization is observed over the same voltage range suggesting a membrane potential-mediated response. Conclusions: Our experiments identify and use subcytotoxic voltages to measure differences in the fraction of E. coli cells elongating and dividing as a function of applied voltage. It is hoped that this research will inform the developing field of bacterial electrophysiology.

What Are the Effects of Irreversible Electroporation on a Staphylococcus aureus Rabbit Model of Osteomyelitis?

BACKGROUND

The treatment of osteomyelitis can be challenging because of poor antibiotic penetration into the infected bone and toxicities associated with prolonged antibiotic regimens to control infection. Irreversible electroporation (IRE), a percutaneous image-guided ablation technology in which the targeted delivery of high-voltage electrical pulses permanently damages the cell membrane, has been shown to effectively control bacterial growth in various settings. However, IRE for the management of bone infections has yet to be evaluated.

QUESTIONS/PURPOSES

We aimed to evaluate IRE for treating osteomyelitis by assessing (1) the efficacy of IRE to suppress the in vitro growth of a clinical isolate of S. aureus, alone or combined with cefazolin; and (2) the effects of IRE on the in vivo treatment of a rabbit model of osteomyelitis.

METHODS

S. aureus strain UAMS-1 expanded in vitro to the log phase was subjected to an electric field of 2700 V/cm, which was delivered in increasing numbers of pulses. Immediately after electroporation, bacteria were plated on agar plates with or without cefazolin. The number of colony-forming units (CFUs) was scored the following day. ANOVA tests were used to analyze in vitro data. In a rabbit osteomyelitis model, we inoculated the same bacterial strain into the radius of adult male New Zealand White rabbits. Three weeks after inoculation, all animals (n = 32) underwent irrigation and débridement, as well as wound culture of the infected forelimb. Then, they were randomly assigned to one of four treatment groups (n = eight per group): untreated control, cefazolin only, IRE only, or combined IRE + cefazolin. Serial radiography was performed to assess disease progression using a semiquantitative grading scale. Bone and soft-tissue specimens from the infected and contralateral forelimbs were collected at 4 weeks after treatment for bacterial isolation and histologic assessment using a semiquantitative scale.

RESULTS

The in vitro growth of S. aureus UAMS-1 was impaired by IRE in a pulse-dependent fashion; the number of CFUs/mL was different among seven pulse levels, namely 0, 10, 30, 60, 90, 120, and 150 pulses. With the number of CFUs/mL observed in untreated controls set as 100%, 10 pulses rendered a median of 50.2% (range 47.1% to 58.2%), 30 pulses rendered a median of 2.7% (range 2.5% to 2.8%), 60 pulses rendered a median of 0.014% (range 0.012% to 0.015%), 90 pulses rendered a median of 0.004% (range 0.002% to 0.004%), 120 pulses rendered a median of 0.001% (range 0.001% to 0.001%), and 150 pulses rendered a median of 0.001% (range 0.000% to 0.001%) (Kruskal-Wallis test: p = 0.003). There was an interaction between the effect of the number of pulses and the concentration of cefazolin (two-way ANOVA: F [8, 30] = 17.24; p < 0.001), indicating that combining IRE with cefazolin is more effective than either treatment alone at suppressing the growth of S. aureus UAMS-1. Likewise, the clinical response in the rabbit model (the percentage of animals without detectable residual bacteria in the bone and surrounding soft tissue after treatment) was better in the combination group than in the other groups: control, 12.5% (one of eight animals); IRE only, 12.5% (one of eight animals); cefazolin only, 25% (two of eight animals); and IRE + cefazolin, 75% (six of eight animals) (two-sided Fisher's exact test: p = 0.030).

CONCLUSIONS

IRE effectively suppressed the growth of S. aureus UAMS-1 and enhanced the antibacterial effect of cefazolin in in vitro studies. When translated to a rabbit osteomyelitis model, the addition of IRE to conventional parenteral antibiotic treatment produced the strongest response, which supports the in vitro findings.

CLINICAL RELEVANCE

Our results show that IRE may improve the results of standard parenteral antibiotic treatment, thus setting the stage for models with larger animals and perhaps trials in humans for validation.

Microfluidic Irreversible Electroporation-A Versatile Tool to Extract Intracellular Contents of Bacteria and Yeast

Exploring the dynamic behavior of cellular metabolism requires a standard laboratory method that guarantees rapid sampling and extraction of the cellular content. We propose a versatile sampling technique applicable to cells with different cell wall and cell membrane properties. The technique is based on irreversible electroporation with simultaneous quenching and extraction by using a microfluidic device. By application of electric pulses in the millisecond range, permanent lethal pores are formed in the cell membrane of Escherichia coli and Saccharomyces cerevisiae, facilitating the release of the cellular contents; here demonstrated by the measurement of glucose-6-phosphate and the activity of the enzyme glucose-6-phosphate dehydrogenase. The successful application of this device was demonstrated by pulsed electric field treatment in a flow-through configuration of the microfluidic chip in combination with sampling, inactivation, and extraction of the intracellular content in a few seconds. Minimum electric field strengths of 10 kV/cm for E. coli and 7.5 kV/cm for yeast S. cerevisiae were required for successful cell lysis. The results are discussed in the context of applications in industrial biotechnology, where metabolomics analyses are important.

Selective Inactivation of Pseudomonas aeruginosa and Staphylococcus epidermidis with Pulsed Electric Fields and Antibiotics

Objective: Increasing numbers of multidrug-resistant bacteria make many antibiotics ineffective; therefore, new approaches to combat microbial infections are needed. In addition, antibiotics are not selective-they kill pathogenic organisms as well as organisms that could positively contribute to wound healing (bio flora). Approach: Here we report on selective inactivation of Pseudomonas aeruginosa and Staphylococcus epidermidis, potential pathogens involved in wound infections with pulsed electric fields (PEFs) and antibiotics (mix of penicillin, streptomycin, and nystatin). Results: Using a Taguchi experimental design in vitro, we found that, under similar electric field strengths, the pulse duration is the most important parameter for P. aeruginosa inactivation, followed by the number of pulses and pulse frequency. P. aeruginosa, a potential severe pathogen, is more sensitive than the less pathogenic S. epidermidis to PEF (alone or in combination with antibiotics). Applying 200 pulses with a duration of 60 μs at 2.8 Hz, the minimum electric fields of 308.8 ± 28.3 and 378.4 ± 12.9 V/mm were required to inactive P. aeruginosa and S. epidermidis, respectively. Addition of antibiotics reduced the threshold for minimum electric fields required to inactivate the bacteria. Innovation: This study provides essential information, such as critical electric field parameters for bacteria inactivation, required for developing in vivo treatment and clinical protocols for using PEF for wound healing. Conclusion: A combination of PEFs with antibiotics reduces the electric field threshold required for bacteria disinfection. Such an approach simplifies devices required to disinfect large areas of infected wounds.

IGBT-Based Pulsed Electric Fields Generator for Disinfection: Design and In Vitro Studies on Pseudomonas aeruginosa

Irreversible electroporation of cell membrane with pulsed electric fields is an emerging physical method for disinfection that aims to reduce the doses and volumes of used antibiotics for wound healing. Here we report on the design of the IGBT-based pulsed electric field generator that enabled eradication of multidrug resistant Pseudomonas aeruginosa PAO1 on the gel. Using a concentric electric configuration we determined that the lower threshold of the electric field required to kill P. aeruginosa PAO1 was 89.28 ± 12.89 V mm^-1, when 200 square pulses of 300 µs duration are delivered at 3 Hz. These parameters disinfected 38.14 ± 0.79 mm² area around the single needle electrode. This study provides a step towards the design of equipment required for multidrug-resistant bacteria disinfection in patients with pulsed electric fields.

Electroactive Smart Polymers for Biomedical Applications

The flexibility in polymer properties has allowed the development of a broad range of materials with electroactivity, such as intrinsically conductive conjugated polymers, percolated conductive composites, and ionic conductive hydrogels. These smart electroactive polymers can be designed to respond rationally under an electric stimulus, triggering outstanding properties suitable for biomedical applications. This review presents a general overview of the potential applications of these electroactive smart polymers in the field of tissue engineering and biomaterials. In particular, details about the ability of these electroactive polymers to: (1) stimulate cells in the context of tissue engineering by providing electrical current; (2) mimic muscles by converting electric energy into mechanical energy through an electromechanical response; (3) deliver drugs by changing their internal configuration under an electrical stimulus; and (4) have antimicrobial behavior due to the conduction of electricity, are discussed.