Effect of nanosecond pulsed electric field on Escherichia coli in water: inactivation and impact on protein changes

Effects of Voltage and Treatment Time of Pulsed Electric Field on Electroporation in Rhizoctonia solani

The pulsed electric field (PEF) of μs duration can induce electroporation by causing permanent damage to the membrane, leading to cell death. The microbe was treated by a homemade PEF generator instrument. The sterilization effect of PEF on the Rhizoctonia solani was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the leakage of the intracellular contents was measured with a conductometer and an ultraviolet spectrophotometer. The increases in the electrical conductivity and the optical density (OD) value indicated that the cell membrane was damaged, and the intracellular contents overflowed. As a result, according to our experimental conditions, the optimum condition was the high-pulsed electric voltage of 26 kV, and the treatment time was 4 min. It could be concluded that the PEF could damage the cell membrane, and the ratio of electroporation reached 100%, which provides a new method of killing R. solani efficiently.

Adoption of water reuse technologies: An assessment under different regulatory and operational scenarios

Water reuse technologies may alleviate the water scarcity problems that affect many world regions, but their adoption is still limited. In particular, key actors in the adoption of water reuse technologies are water utilities, that provide both urban water and wastewater treatment services. Water utilities are embedded in the urban water system, which includes several stakeholders (urban water users, citizens at large, the environment) that may drive or pose barriers to water reuse adoption. Therefore, to ensure a smooth introduction of water reuse technologies, it is fundamental to understand how water reuse interacts with the existing urban water system and impacts its stakeholders. This paper contributes to the ongoing debate on water reuse by conceptualizing the interaction between water reuse technologies and the urban water system and its stakeholders, and addressing the adoption decision of water utilities by assessing its economic and environmental consequences. Based on a review of literature, policy and other secondary documents, and on primary data coming from interviews with experts from a water utility operating in Southern Italy, the study models the utility's response to a shift from urban to reuse water. It then simulates how reuse water introduction impacts on the utility and other stakeholders of the water system, under various regulatory and operational scenarios defined through a thorough analysis of policy documents and literature. Results show that the adoption of water reuse reduces the utility's margin by cannibalizing urban water demand, but appropriate policy measures may enhance the economic sustainability of reuse. System-level performances, such as impact on freshwater savings, costs for users, effects on the public budget, are also assessed, showing how different regulatory options moderate the intensity of impacts for the different stakeholders of the water system. Furthermore, the adoption of reuse water by the most distant users is found to enhance the economic sustainability of reuse and positively impact the utility's margin.

High Frequency Bipolar Electroporator with Double-Crowbar Circuit for Load-Independent Forming of Nanosecond Pulses

In this work, a novel electroporation system (electroporator) is presented, which is capable of forming high frequency pulses in a broad range of parameters (65 ns–100 µs). The electroporator supports voltages up to 3 kV and currents up to 40 A and is based on H-bridge circuit topology. A synchronized double crowbar driving sequence is introduced to generate short nanosecond range pulses independently of the electroporator load. The resultant circuit generates pulses with repetition frequencies up to 5 MHz and supports unipolar, bipolar, and asymmetrical pulse sequences with arbitrary waveforms. The shortest pulse duration step is hardware limited to 33 ns. The electroporator was experimentally tested on the H69AR human lung cancer cell line using 20 kV/cm bipolar and unipolar 100 ns–1 μs pulses. Based on a YO-PRO-1 permeabilization assay, it was determined that the electroporator is suitable for applied research on electroporation. The system offers high flexibility in experimental design to trigger various electroporation-based phenomena.

Growth in a biofilm sensitizes Cutibacterium acnes to nanosecond pulsed electric fields

The Gram-positive anaerobic bacterium Cutibacterium acnes (C. acnes) is a commensal of the human skin, but also an opportunistic pathogen that contributes to the pathophysiology of the skin disease acne vulgaris. C. acnes can form biofilms; cells in biofilms are more resilient to antimicrobial stresses. Acne therapeutic options such as topical or systemic antimicrobial treatments often show incomplete responses. In this study we measured the efficacy of nanosecond pulsed electric fields (nsPEF), a new promising cell and tissue ablation technology, to inactivate C. acnes. Our results show that all tested nsPEF doses (250 to 2000 pulses, 280 ns pulses, 28 kV/cm, 5 Hz; 0.5 to 4 kJ/ml) failed to inactivate planktonic C. acnes and that pretreatment with lysozyme, a naturally occurring cell-wall-weakening enzyme, increased C. acnes vulnerability to nsPEF. Surprisingly, growth in a biofilm appears to sensitize C. acnes to nsPEF-induced stress, as C. acnes biofilm-derived cells showed increased cell death after nsPEF treatments that did not affect planktonic cells. Biofilm inactivation by nsPEF was confirmed by treating intact biofilms grown on glass coverslips with an indium oxide conductive layer. Altogether our results show that, contrary to other antimicrobial agents, nsPEF kill more efficiently bacteria in biofilms than planktonic cells.

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.

Pulsed electric field and mild heating for milk processing: a review on recent advances

Pulsed electric field (PEF) treatment consists of exposing food to electrical fields between electrodes within a treatment chamber, which can improve the preservation of fresh-like products such as milk. Although several studies support the use of PEF technology to process milk at low temperature, these studies reported microbial reductions of around 3 log₁₀ cycles and also indicated a limited impact of PEF on some endogenous and microbial enzymes. This scenario indicates that increasing the impact of PEF on both enzymes and microorganisms remains a major challenge for this technology in milk processing. More recently, combining PEF with mild heating (below pasteurization condition) has been explored as an alternative processing technology to enhance the safety and to preserve the quality of fresh milk and milk products. Mild heating with PEF enhanced the safety of milk and derived products (3 log₁₀ -6 log₁₀ cycles reduction on microbial load and drastic impact on the activity enzymes related to quality decay). Moreover, with this approach, there was minimal impact on enzymes of technological and safety relevance, proteins, milk fat globules, and nutrients (particularly for vitamins) and improvements in the shelf-life of milk and selected derived products were obtained. Finally, further experiments should consider the use of milk processed by PEF with mild heating on cheese-making. The combined approach of PEF with mild heating to process milk and derived products is very promising. The characteristics of current PEF systems (which is being used at an industrial level in several countries) and their use in the liquid food industry, particularly for milk and some milk products, could advance towards this strategy. © 2019 Society of Chemical Industry.

Proteomics-Based Mechanistic Investigation of Escherichia coli Inactivation by Pulsed Electric Field

The pulsed electric field (PEF) technology has been widely applied to inactivate pathogenic bacteria in food products. Though irreversible pore formation and membrane disruption is considered to be the main contributing factor to PEF's sterilizing effects, the exact molecular mechanisms remain poorly understood. In this study, by using mass spectrometry (MS)-based label-free quantitative proteomic analysis, we compared the protein profiles of PEF-treated and untreated Escherichia coli. We identified a total of 175 differentially expressed proteins, including 52 candidates that were only detected in at least two of the three samples in one experiment group but not in the other group. Functional analysis revealed that the differential proteins were primarily involved in the regulation of cell membrane composition and integrity, stress response, as well as various metabolic processes. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis was conducted on the genes of selected differential proteins at varying PEF intensities, which were known to result in different cell killing levels. The qRT-PCR data confirmed that the proteomic results could be reliably used for further data interpretation, and that the changes in the expression levels of the differential candidates were, to a large extent, caused directly by the PEF treatment. The findings of the current study offered valuable insight into PEF-induced cell inactivation.

Low concentrations of acetic and formic acids enhance the inactivation of Staphylococcus aureus and Pseudomonas aeruginosa with pulsed electric fields

Background

Skin infections, particularly caused by drug-resistant pathogens, represent a clinical challenge due to being a frequent cause of morbidity and mortality. The objectives of this study were to examine if low concentrations of acetic and formic acids can increase sensitivity of Staphylococcus aureus and Pseudomonas aeruginosa to pulsed electric field (PEF) and thus, promote a fast and efficient treatment methodology for wound treatment.

Results

We have shown that the combination of PEF (10–30 kV/cm) with organic acids (0.1% formic and acetic acids) increased the bactericidal properties of treatment. The effect was apparent for both acids. The proposed methodology allowed to reduce the energy of electrical pulses and the inhibitory concentrations of acids, while still maintain high efficiency of bacteria eradication.

Conclusions

Application of weak organic acids as bactericidal agents has many advantages over antibiotics because they do not trigger development of drug-resistance in bacteria. The combination with PEF can make the treatment effective even against biofilms. The results of this study are particularly useful for the development of new methodologies for the treatment of extreme cases of wound infections when the chemical treatment is no longer effective or hinders wound healing.

Inactivation of Escherichia coli Using Nanosecond Electric Fields and Nisin Nanoparticles: A Kinetics Study

Nisin is a recognized bacteriocin widely used in food processing, however, being ineffective against gram-negative bacteria and in complex food systems. As a result, the research of methods that have cell wall–permeabilizing activity is required. In this study, electroporation to trigger sensitization of gram-negative bacteria to nisin-loaded pectin nanoparticles was used. As a model microorganism, bioluminescent strain of E. coli was introduced. Inactivation kinetics using nanosecond pulsed electric fields (PEFs) and nisin nanoparticles have been studied in a broad range (100–900 ns, 10–30 kV/cm) of pulse parameters. As a reference, the microsecond range protocols (100 μs × 8) have been applied. It was determined that the 20–30 kV/cm electric field with pulse duration ranging from 500 to 900 ns was sufficient to cause significant permeabilization of E. coli to trigger a synergistic response with the nisin treatment. The kinetics of the inactivation was studied with a time resolution of 2.5 min, which provided experimental evidence that the efficacy of nisin-based treatment can be effectively controlled in time using PEF. The results and the proposed methodology for rapid detection of bacteria inactivation rate based on bioluminescence may be useful in the development and optimization of protocols for PEF-based treatments.

Nanosecond range electric pulse application as a non-viral gene delivery method: proof of concept

Current electrotransfection protocols are well-established for decades and, as a rule, employ long micro-millisecond range electric field pulses to facilitate DNA transfer while application of nanosecond range pulses is limited. The purpose of this paper is to show that the transfection using ultrashort pulses is possible by regulating the pulse repetition frequency. We have used 200 ns pulses (10-18 kV/cm) in bursts of ten with varied repetition frequency (1 Hz-1 MHz). The Chinese Hamster Ovary (CHO) cells were used as a cell model. Experiments were performed using green fluorescent protein (GFP) and luciferase (LUC) coding plasmids. Transfection expression levels were evaluated using flow cytometry or luminometer. It was shown that with the increase of frequency from 100 kHz to 1 MHz, the transfection expression levels increased up to 17% with minimal decrease in cell viability. The LUC coding plasmid was transferred more efficiently using high frequency bursts compared to single pulses of equivalent energy. The first proof of concept for frequency-controlled nanosecond electrotransfection was shown, which can find application as a new non-viral gene delivery method.

Enhanced Antimicrobial Activity Based on a Synergistic Combination of Sublethal Levels of Stresses Induced by UV-A Light and Organic Acids

The reduction of microbial load in food and water systems is critical for their safety and shelf life. Conventionally, physical processes such as heat or light are used for the rapid inactivation of microbes, while natural compounds such as lactic acid may be used as preservatives after the initial physical process. This study demonstrates the enhanced and rapid inactivation of bacteria based on a synergistic combination of sublethal levels of stresses induced by UV-A light and two food-grade organic acids. A reduction of 4.7 ± 0.5 log CFU/ml in Escherichia coli O157:H7 was observed using a synergistic combination of UV-A light, gallic acid (GA), and lactic acid (LA), while the individual treatments and the combination of individual organic acids with UV-A light resulted in a reduction of less than 1 log CFU/ml. Enhanced inactivation of bacteria on the surfaces of lettuce and spinach leaves was also observed based on the synergistic combination. Mechanistic investigations suggested that the treatment with a synergistic combination of GA plus LA plus UV-A (GA+LA+UV-A) resulted in significant increases in membrane permeability and intracellular thiol oxidation and affected the metabolic machinery of E. coli In addition, the antimicrobial activity of the synergistic combination of GA+LA+UV-A was effective only against metabolically active E. coli O157:H7. In summary, this study illustrates the potential of simultaneously using a combination of sublethal concentrations of natural antimicrobials and a low level of physical stress in the form of UV-A light to inactivate bacteria in water and food systems.IMPORTANCE There is a critical unmet need to improve the microbial safety of the food supply, while retaining optimal nutritional and sensory properties of food. Furthermore, there is a need to develop novel technologies that can reduce the impact of food processing operations on energy and water resources. Conventionally, physical processes such as heat and light are used for inactivating microbes in food products, but these processes often significantly reduce the sensory and nutritional properties of food and are highly energy intensive. This study demonstrates that the combination of two natural food-grade antimicrobial agents with a sublethal level of physical stress in the form of UV-A light can greatly increase microbial load inactivation. In addition, this report elucidates the potential mechanisms for this synergistic interaction among physical and chemical stresses. Overall, these results provide a novel approach to develop antimicrobial solutions for food and water systems.

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.

Controlled inactivation of Trichophyton rubrum using shaped electrical pulse bursts: Parametric analysis

The dermatophytes infect the skin by adherence to the epidermis followed by germination, growth, and penetration of the fungal hyphae within the cells. The aim of this study was to investigate the efficacy of the pulsed electric fields (PEF) of controlled inactivation of Trichophyton rubrum (ATCC 28188). In this work, we have used bursts of the square wave PEF pulses of different intensity (10-30 kV/cm) to induce the irreversible inactivation in vitro. The electric field pulses of 50 µs and 100 µs have been generated in bursts of 5, 10, and 20 pulses with repetition frequency of 1 Hz. The dynamics of the inactivation using different treatment parameters were studied and the inactivation map for the T. rubrum has been defined. Further, the combined effect of PEF with the antifungal agents itraconazole, terbinafine, and naftifine HCl was investigated. It has been demonstrated that the combined effect results in the full inactivation of T. rubrum colony. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1056-1060, 2016.