Nanosecond electric pulses rapidly enhance the inactivation of Gram-negative bacteria using Gram-positive antibiotics

Application of pulsed electric field (PEF) as a strategy to enhance aminoglycosides efficacy against Gram-negative bacteria

In this study, two aminoglycosides (AGs), Kanamycin and Gentamicin, with similar modes of action and molecular weights, were combined with PEF treatment to enhance the inactivation of E. coli cells. Various PEF strengths were applied to assess the combined effect. To compare the inactivation efficacy of different AGs, bacterial growth measurements in suspension were performed at 3 and 10 h intervals over a 10-h period after PEF treatment. Interestingly, it was found that the additive effect of PEF treatment on E. coli growth inhibition was significantly greater with Kanamycin (IC50) than with Gentamicin (IC50). Further analysis revealed that the combined treatment with Kanamycin (IC50) was most effective within a timeframe of around 3 h. Our findings suggest that PEF treatment can significantly enhance the efficacy of AGs against Gram-negative bacteria; however, the extent of the additive effect varies depending on the specific antibiotic and the intensity of the applied PEF treatment.

Maps of Membrane Pore Dynamics From Picosecond to Millisecond Pulse Durations

Electroporation occurs when cells are exposed to an electric pulse of sufficient intensity and pulse duration . Many studies have attempted to develop universal scaling laws to predict membrane pore dynamics for pulsed electric fields (PEFs) of different durations; however, the differences in pore dynamics across these parameters makes this difficult both experimentally and numerically. This study uses the asymptotic Smoluchowski equation (ASME) to quantify the number of pores, average pore radius, and fractional pore area (FPA) during exposure to PEFs with durations from hundreds of picoseconds to a millisecond. We highlight pulse parameter regimes that favor increases in pore radius and number and show that the FPA is dominated by the number of pores formed on the cell membrane. Furthermore, the number of pores and the FPA depend almost entirely on for exceeding the charging time of the cell and both and for shorter than the charging time. Finally, the maps of pore number, average radius, and FPA demonstrate that a universal scaling law for pore dynamics across a wide range of pulse durations does not exist, although certain scaling behaviors may be valuable over narrow regimes. Practically, these maps provide a guideline for selecting PEF parameters to achieve desired membrane permeabilization.

Synergistic Potential of Antibiotics with Cancer Treatments

Intratumoral microbiota, the diverse community of microorganisms residing within tumor tissues, represent an emerging and intriguing field in cancer biology. These microbial populations are distinct from the well-studied gut microbiota, offering novel insights into tumor biology, cancer progression, and potential therapeutic interventions. Recent studies have explored the use of certain antibiotics to modulate intratumoral microbiota and enhance the efficacy of cancer therapies, showing promising results. Antibiotics can alter intratumoral microbiota's composition, which may have a major role in promoting cancer progression and immune evasion. Certain bacteria within tumors can promote immunosuppression and resistance to therapies. By targeting these bacteria, antibiotics can help create a more favorable environment for chemotherapy, targeted therapy, and immunotherapy to act effectively. Some bacteria within the tumor microenvironment produce immunosuppressive molecules that inhibit the activity of immune cells. The combination of antibiotics and other cancer therapies holds significant promise for creating a synergistic effect and enhancing the immune response against cancer. In this review, we analyze several preclinical studies that have been conducted to demonstrate the synergy between antibiotics and other cancer therapies and discuss possible clinical implications.

Inactivation of bacteria using synergistic hydrogen peroxide with split-dose nanosecond pulsed electric field exposures

The use of pulsed electric fields (PEF) as a nonthermal technology for the decontamination of foods is of growing interest. This study aimed to enhance the inactivation of Escherichia coli, Listeria innocua, and Salmonella enterica in Gomori buffer using a combination of nsPEF and hydrogen peroxide (H2O2). Three sub-MIC concentrations (0.1, 0.3, and 0.5%) of H2O2 and various contact times ranging from 5-45 min were tested. PEF exposures as both single (1000 pulse) and split-dose (500+500 pulse) trains were delivered via square-wave, monopolar, 600 ns pulses at 21 kV/cm and 10 Hz. We demonstrate that >5 log CFU/mL reduction can be attained from combination PEF/H2O2 treatments with a 15 min contact time for E. coli (0.1%) and a 30 min contact time for L. innocua and S. enterica (0.5%), despite ineffective results from either individual treatment alone. A 5 log reduction in microbial population is generally the lowest acceptable level in consideration of food safety and represents inactivation of 99.999% of bacteria. Split-dose PEF exposures enhance lethality for several tested conditions, indicating greater susceptibility to PEF after oxidative damage has occurred.

Electro-antibacterial therapy (EAT) to enhance intracellular bacteria clearance in pancreatic cancer cells

Intratumoral bacteria have been implicated in driving tumor progression, yet effective treatments to modulate the tumor microbiome remain limited. In this study, we investigate the use of electroporation in combination with metronidazole to enhance the clearance of intracellular Fusobacterium nucleatum within pancreatic cancer cells. We explore various parameters, including electric field strength, pulse width, and pulse number to assess the permeability of pancreatic cancer cells infected with F. nucleatum, compared to non-infected cells of the same type. We subsequently quantify the clearance of intracellular bacteria when these pulsing schemes are applied to a suspension of infected pancreatic cancer cells in the presence of metronidazole. Our results reveal distinct differences in cell permeability between infected and non-infected cells, identifying a unique biophysical marker for host cells infected with F. nucleatum. We demonstrate that the combinatorial use of electroporation and metronidazole significantly enhances the delivery of metronidazole into host cells, leading to more effective clearance of intracellular F. nucleatum compared to independent treatments; we term this novel approach Electro-Antibacterial Therapy (EAT). EAT holds promise as an innovative strategy for addressing intratumoral bacteria in pancreatic cancer, other malignancies, and potentially treatment-resistant infections, offering new avenues for therapeutic intervention.

Antibiotic's target site affects the potentiation of Lactiplantibacillus plantarum inhibition and inactivation by electroporation

Introduction

Antibiotic resistance represents a growing global threat, and thus the motivation to develop novel and combined methods of bacterial inactivation is increasing. Electroporation is a technique in which electric pulses of sufficient strength are applied to permeabilize cells, including bacteria. Combining antibacterials with electroporation is a promising strategy to potentiate their bactericidal and bacteriostatic effectiveness. This approach has already proved useful for increasing bacterial inactivation, yet most studies so far have mainly focused on the maximal achievable effects, and less on the underlying mechanisms. We recently demonstrated that in the Gram-negative (G-) bacterium Escherichia coli, electroporation potentiates antibacterials targeting the peptidoglycan wall more than those with intracellular targets. However, in Gram-positive (G+) bacteria, the wall is directly accessible from the outside, and thus the dependence of potentiation on the antibacterial's target may be rather different. Here, we compare the inactivation and growth inhibition of the G+ bacterium Lactiplantibacillus plantarum for two antibiotics with different modes of action: ampicillin (inhibits cell-wall synthesis) and tetracycline (inhibits intracellular protein synthesis).

Methods

We used antibiotic concentrations ranging from 0 to 30 × MIC (minimum inhibitory concentration that we predetermined for each antibiotic), a single 1-ms electric pulse with an amplitude from 0 to 20 kV/cm, and post-pulse pre-dilution incubation of 24 h or 1 h.

Results

Electroporation increased the inhibition and inactivation efficiency of both antibiotics, but this was more pronounced for tetracycline, with statistical significance mostly limited to 24-h incubation. In general, both inhibition and inactivation grew stronger with increasing antibiotic concentration and electric field amplitude.

Discussion

Our results indicate that electroporation potentiates inactivation of G+ bacteria to a larger extent for antibiotics that inhibit intracellular processes and require transport into the cytoplasm, and to a smaller extent for antibiotics that inhibit cell-wall synthesis. This is the inverse of the relation observed in G- bacteria, and can be explained by the difference in the envelope structure: in G- bacteria the outer membrane must be breached for wall-inhibiting antibiotics to access their target, whereas in G+ bacteria the wall is inherently accessible from the outside and permeabilization does not affect this access.

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.

Nanosecond pulsed electric fields increase antibiotic susceptibility in methicillin-resistant Staphylococcus aureus

IMPORTANCE

We have found that treatment with short electric pulses potentiates the effects of multiple antibiotics against methicillin-resistant Staphylococcus aureus. By reducing the dose of antibiotic necessary to be effective, co-treatment with electric pulses could amplify the effects of standard antibiotic dosing to treat S. aureus infections such as skin and soft-tissue infections (SSTIs). SSTIs are accessible to physical intervention and are good candidates for electric pulse co-treatment, which could be adopted as a step-in wound and abscess debridement.

Biocompatibility and Safety Assessment of Combined Topical Ozone and Antibiotics for Treatment of Infected Wounds

Wound infections with antibiotic-resistant bacteria, particularly the Gram-negative strains, pose a substantial health risk for patients with limited treatment options. Recently topical administration of gaseous ozone and its combination with antibiotics through portable systems has been demonstrated to be a promising approach to eradicate commonly found Gram-negative strains of bacteria in wound infections. However, despite the significant impact of ozone in treating the growing number of antibiotic-resistant infections, uncontrolled and high concentrations of ozone can cause damage to the surrounding tissue. Hence, before such treatments could advance into clinical usage, it is paramount to identify appropriate levels of topical ozone that are effective in treating bacterial infections and safe for use in topical administration. To address this concern, we have conducted a series of in vivo studies to evaluate the efficacy and safety of a portable and wearable adjunct ozone and antibiotic wound therapy system. The concurrent ozone and antibiotics are applied through a wound interfaced gas permeable dressing coated with water-soluble nanofibers containing vancomycin and linezolid (traditionally used to treat Gram-positive infections) and connected to a portable ozone delivery system. The bactericidal properties of the combination therapy were evaluated on an ex vivo wound model infected with Pseudomonas aeruginosa, a common Gram-negative strain of bacteria found in many skin infections with high resistance to a wide range of currently available antibiotics. The results indicated that the optimized combination delivery of ozone (4 mg h^-1) and topical antibiotic (200 μg cm^-2) provided complete bacteria eradication after 6 h of treatment while having minimum cytotoxicity to human fibroblast cells. Furthermore, in vivo local and systemic toxicity studies (e.g., skin monitoring, skin histopathology, and blood analysis) on pig models showed no signs of adverse effects of ozone and antibiotic combination therapy even after 5 days of continuous administration. The confirmed efficacy and biosafety profile of the adjunct ozone and antibiotic therapy places it as a strong candidate for treating wound infection with antimicrobial-resistant bacteria and further pursuing human clinical trials.

Wearable adjunct ozone and antibiotic therapy system for treatment of Gram-negative dermal bacterial infection

The problematic combination of a rising prevalence of skin and soft tissue infections and the growing rate of life-threatening antibiotic resistant infections presents an urgent, unmet need for the healthcare industry. These evolutionary resistances originate from mutations in the bacterial cell walls which prevent effective diffusion of antibiotics. Gram-negative bacteria are of special consideration due to the natural resistance to many common antibiotics due to the unique bilayer structure of the cell wall. The system developed here provides one solution to this problem through a wearable therapy that delivers and utilizes gaseous ozone as an adjunct therapy with topical antibiotics through a novel dressing with drug-eluting nanofibers (NFs). This technology drastically increases the sensitivity of Gram-negative bacteria to common antibiotics by using oxidative ozone to bypass resistances created by the bacterial cell wall. To enable simple and effective application of adjunct therapy, ozone delivery and topical antibiotics have been integrated into a single application patch. The drug delivery NFs are generated via electrospinning in a fast-dissolve PVA mat without inducing decreasing gas permeability of the dressing. A systematic study found ozone generation at 4 mg/h provided optimal ozone levels for high antimicrobial performance with minimal cytotoxicity. This ozone treatment was used with adjunct therapy delivered by the system in vitro. Results showed complete eradication of Gram-negative bacteria with ozone and antibiotics typically used only for Gram-positive bacteria, which showed the strength of ozone as an enabling adjunct treatment option to sensitize bacteria strains to otherwise ineffective antibiotics. Furthermore, the treatment is shown through biocompatibility testing to exhibit no cytotoxic effect on human fibroblast cells.

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.

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.

Emerging antibacterial nanomedicine for enhanced antibiotic therapy

This review highlights the different mechanisms of current nano-antibiotic systems for combatting serious antibiotic resistance of bacteria.