The growth of Staphylococcus aureus and Escherichia coli in low-direct current electric fields

Electrical hydrogel: electrophysiological-based strategy for wound healing

Wound healing remains a significant challenge in clinical practice, driving ongoing exploration of innovative therapeutic approaches. In recent years, electrophysiological-based wound healing strategies have gained considerable attention. Specifically, electrical hydrogels combine the synergistic effects of electrical stimulation and hydrogel properties, offering a range of functional benefits for wound healing, including antibacterial activity, real-time wound monitoring, controlled drug release, and electrical treatment. Despite significant progress made in electrical hydrogel research for wound healing, there is a lack of comprehensive, systematic reviews summarizing this field. In this review, we survey the latest advancements in electrical hydrogel technology. After analyzing the mechanisms of electrical stimulation in promoting wound healing, we establish a novel classification framework for electrical hydrogels based on their operational principles. The review further provides an in-depth evaluation of the therapeutic efficacy of these hydrogels in various types of wounds. Finally, we propose future directions and challenges for the development of electrical hydrogels for wound healing.

Zirconia Dental Implants Surface Electric Stimulation Impact on Staphylococcus aureus

Tooth loss during the lifetime of an individual is common. A strategy to treat partial or complete edentulous patients is the placement of dental implants. However, dental implants are subject to bacterial colonization and biofilm formation, which cause an infection named peri-implantitis. The existing long-term treatments for peri-implantitis are generally inefficient. Thus, an electrical circuit was produced with zirconia (Zr) samples using a hot-pressing technique to impregnate silver (Ag) through channels and holes to create a path by LASER texturing. The obtained specimens were characterized according to vitro cytotoxicity, to ensure ZrAg non-toxicity. Furthermore, samples were inoculated with Staphylococcus aureus using 6.5 mA of alternating current (AC). The current was delivered using a potentiostat and the influence on the bacterial concentration was assessed. Using AC, the specimens displayed no bacterial adhesion (Log 7 reduction). The in vitro results presented in this study suggest that this kind of treatment can be an alternative and promising strategy to treat and overcome bacterial adhesion around dental implants that can evolve to biofilm.

The antibacterial mechanism of compound preservatives combined with low voltage electric fields on the preservation of steamed mussels (Mytilus edulis) stored at ice-temperature

Mussels are a kind of economically valuable ocean bivalve shellfish. It has a short harvest period and is susceptible to contamination during storage and processing. Having proper preservation methods is critical to prevent quality deterioration. However, the effect of low voltage variable frequency electric field and compound preservative on the freshness of steamed mussels in ice-temperature storage are still unknown. We utilized the method of coefficient variation weighting to calculate the overall scores of steamed mussels stored under different preservation conditions. The protein physicochemical properties of samples, the growth curves of two dominant spoilage bacteria; Bacillus subtilis and Pseudomonas in the mussels as well as the Structural changes of the cell membranes were mensurated. The results show that compared with the preservative group and the low voltage variable frequency electric field group, the compound preservatives combined with the electric field group had the highest overall score and thus the best preservation effect. Compared with the blank group, the total sulfhydryl content and myogenic fibrin content of the combined group decreased at the slowest rate, 19.46%, and 44.92%, respectively. The hydrophobicity of the protein surface increased by only 5.67%, with the best water retention, indicating that the samples of the combined group had the least protein deterioration in the combined group. The inhibition mechanism of the combined group inhibited the growth of two dominant spoilage bacteria: Bacillus subtilis and Pseudomonas, in the mussels, destroying the integrity of the cell membrane structure and changing the cell morphology. Overall, we found that the combination of the composite preservatives and the low voltage variable frequency electric field can maintain the best quality of steamed mussels during ice-temperature storage and slow down the rate of protein deterioration during storage. This study proposed a new method of mussel preservation, which provides a new idea for the application of low voltage variable frequency electric field and compound preservative in the preservation of aquatic products.

Rotating Magnetic Field Increases β-Lactam Antibiotic Susceptibility of Methicillin-Resistant Staphylococcus aureus Strains

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have developed resistance to most β-lactam antibiotics and have become a global health issue. In this work, we analyzed the impact of a rotating magnetic field (RMF) of well-defined and strictly controlled characteristics coupled with β-lactam antibiotics against a total of 28 methicillin-resistant and sensitive S. aureus strains. The results indicate that the application of RMF combined with β-lactam antibiotics correlated with favorable changes in growth inhibition zones or in minimal inhibitory concentrations of the antibiotics compared to controls unexposed to RMF. Fluorescence microscopy indicated a drop in the relative number of cells with intact cell walls after exposure to RMF. These findings were additionally supported by the use of SEM and TEM microscopy, which revealed morphological alterations of RMF-exposed cells manifested by change of shape, drop in cell wall density and cytoplasm condensation. The obtained results indicate that the originally limited impact of β-lactam antibiotics in MRSA is boosted by the disturbances caused by RMF in the bacterial cell walls. Taking into account the high clinical need for new therapeutic options, effective against MRSA, the data presented in this study have high developmental potential and could serve as a basis for new treatment options for MRSA infections.

Eltarahony M, E. Moustafa M. The impact of titanium oxide nanoparticles and low direct electric current on biofilm dispersal of $Bacillus~cereus$ and $Pseudomonas~aeruginosa$: A comparative study

Bacteria growing in biofilms cause a wide range of environmental, industrial and public health risks. Because biofilm bacteria are very resistant to antibiotics, there is an urgent need in medicine and industry to develop new approaches to eliminating bacterial biofilms. One strategy for controlling these biofilms is to generate an antibiofilm substance locally at the attachment surface. Direct electric current (DC) and nanoparticles (NPs) of metal oxides have outstanding antimicrobial properties. In this study we evaluated the effect of titanium oxide nanoparticle (TiO$_2$-NP) concentrations from 5 to 160 $\mu$g/mL on Bacillus cereus and Pseudomonas aeruginosa biofilms, and compared this with the effect of a 9 V, 6 mA DC electric field for 5, 10 and 15 min. TiO$_2$-NPs were characterized using transmission and scanning electron microscopes, X-ray diffraction and FTIR. They exhibited an average size of 22-34 nm. The TiO$_2$-NP concentrations that attained LD50 were $104 \pm 4$ $\mu$g/mL and $63 \pm 3$ $\mu$g/mL for B. cereus and P. aeruginosa, respectively. The eradication percentages obtained by DC at 5, 10, and 15 min exposure were 21%, 29%, and 33% respectively for B. cereus and 30%, 39%, and 44% respectively for P. aeruginosa. Biofilm disintegration was verified by exopolysaccharide, protein content and cell surface hydrophobicity assessment, as well as scanning electron microscopy. These data were correlated with the reactive oxygen species produced. The results indicated that both DC and TiO$_2$-NPs have a lethal effect on these bacterial biofilms, and that the DC conditions used affect the biofilms in a similar way to TiO$_2$-NPs at concentrations of 20-40 $\mu$g/mL.

Investigation of Antimicrobial Activity of DBD Air Plasma-Treated Banana Fabric Coated with Natural Leaf Extracts

This paper focuses on the investigation of the antimicrobial activity of banana fabric treated with dielectric barrier discharge (DBD) plasma. The fabric was exposed to air plasma for varying treatment times of 1-5 min followed by coating with green tea (Camellia sinensis) and tulsi (Ocimum sanctum) leaf extracts at five different concentrations. The treated fabric was evaluated in terms of surface wettability by a range of tests like wet-out time analysis, hydrophilicity test, and contact angle measurements. The functional groups formed on the treated fabric were analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The surface morphology was studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the surface chemistry was studied using X-ray photoelectron spectroscopy (XPS). The FTIR and XPS analysis results indicate that the plasma-treated fabric was found to have a higher concentration of polar groups (-COOH, -OH, -C=O) that has improved surface hydrophilicity and functionality. The antimicrobial activity of the treated fabric surface was determined both qualitatively and quantitatively by the agar plate method and modified Hoenstein test, against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. An improvement in the antimicrobial property was observed in plasma-treated banana fabric coated with natural extracts even after four washing cycles. This study suggests that air DBD plasma treatment followed by the absorption of tea/tulsi leaf extracts can serve as a better tool for developing natural antimicrobial textiles, which could serve the purpose in medical and healthcare sectors concerning recent times. It has eventually led to better absorption of plant extracts, thereby increasing their antimicrobial activity.

Distribution of AC Electric Field-Induced Transmembrane Voltage in Escherichia coli Cell Wall Layers

On the basis of Gram-negative bacterium Escherichia coli models previously published in the literature, the transmembrane voltage induced by the application of an alternating current (AC) electric field on a bacterial suspension is calculated using COMSOL Multiphysics software, in the range 1-20 MHz, for longitudinal and transverse field orientations. The voltages developed on each of the three layers of the cell wall are then calculated using an electrical equivalent circuit. This study shows that the overall voltage on the cell wall, whose order of magnitude is a few tens of µV, is mainly distributed on inner and outer layers, while a near-zero voltage is found on the periplasm, due to its much higher electrical conductivity compared with the other layers. Although the outer membrane electrical conductivity taken in the model is a thousand times higher than that of the inner membrane, the voltage there is about half of that on the inner membrane, due to capacitive effects. It follows that the expression of protein complexes anchored in the inner membrane could potentially be disrupted, inducing in particular a possible perturbation of biological processes related to cellular respiration and proton cycle, and leading to growth inhibition as a consequence. Protein complexes anchored in the outer membrane or constituting a bridge between the three layers of the cell wall, such as some porins, may also undergo the same action, which would add another growth inhibition factor, as a result of deficiency in porin filtration function when the external environment contains biocides. Bioelectromagnetics. 2020;41:279-288 © 2020 Bioelectromagnetics Society.

Electroactive 3D Printed Scaffolds Based on Percolated Composites of Polycaprolactone With Thermally Reduced Graphene Oxide for Antibacterial and Tissue Engineering Applications

Applying electrical stimulation (ES) could affect different cellular mechanisms, thereby producing a bactericidal effect and an increase in human cell viability. Despite its relevance, this bioelectric effect has been barely reported in percolated conductive biopolymers. In this context, electroactive polycaprolactone (PCL) scaffolds with conductive Thermally Reduced Graphene Oxide (TrGO) nanoparticles were obtained by a 3D printing method. Under direct current (DC) along the percolated scaffolds, a strong antibacterial effect was observed, which completely eradicated S. aureus on the surface of scaffolds. Notably, the same ES regime also produced a four-fold increase in the viability of human mesenchymal stem cells attached to the 3D conductive PCL/TrGO scaffold compared with the pure PCL scaffold. These results have widened the design of novel electroactive composite polymers that could both eliminate the bacteria adhered to the scaffold and increase human cell viability, which have great potential in tissue engineering applications.

Reduction of Escherichia Coli Using Metal Plates with the Influenced of Applied Low Current and Physical Barrier of Filter Layers

Although metal contact is known to reduce bacterial growth, the effects of physical barriers and electricity need further investigation. This study examined the bacteria-reducing properties of copper and stainless-steel metal plates with an added electrical current and up to three filter layers on the growth of Escherichia coli (bacteria) and MS2 bacteriophages (virus). When used with a stainless-steel plate, electricity increased bacteria reduction by 39.5 ± 2.30% in comparison with no electricity added, whereas a three-layer physical barrier decreased its efficiency. Copper also reduced the growth of bacteria, by 58.2 ± 8.23%, and the addition of electricity reduced it further (79.5 ± 2.34%). Bacteriophages were also affected by the metal contact. Further experiments showed that MS2 was also reduced by copper, to 82.9 ± 4.5% after 24 h at 37 °C.

Alternating electric fields induce a period-dependent motion of Escherichia coli in three-dimension near a conductive surface

It has been demonstrated that electric fields can minimize surface adhesion of bacteria, but how they affect the near-surface bacterial dynamics has remained largely overlooked. In the present study, the three-dimensional motions of Escherichia coli (E. coli) HCB1 and HCB1414 near a conductive surface under alternating-current (AC) electric fields were monitored with digital holographic microscopy. The period (T) of AC fields exhibited profound effects on near-surface bacterial behavioral patterns and thus affected the surface adhesiveness of E. coli. When T ≥ 1 s, HCB1 cells tumble frequently, and both two strain cells increasingly undergo subdiffusive motions compared to the case without electric fields. The bacterial density near the surface varies due to galvanotaxis depending on the initial polarization of the surface. For shorter periods (T ≤ 0.1 s), the electric fields reduce the near-surface bacterial density by 10%-20% with the surface as either an anode or a cathode. The AC fields directly disturb the intrinsic bacterial rotation. The bacterial body exhibits strong wobbling at T ≥ 1 s. Such wobbling was suppressed with decreasing T, which reduces the collisions between E. coli and the surface and thus leads to declining bacterial density. These results suggest that the use of low-density AC fields with tunable T may be a promising antifouling strategy and merits further investigations.

Natural extracted aerogels with inherent anisotropy and their 3D printing assisted biomedical applications

Exemplified with jackfruit and sugarcane, natural extracted aerogels with inherent structural anisotropy were investigated for the first time. With the help of nano-modification, the dual liquid/current directing capability of the Ag decorated jackfruit aerogel was discovered. This interesting material was then applied as the core component of a 3D printed wearable device for intelligent wound management. The as-prepared ultra-light (<10 g) wearable device could provide drainage diversion, wound warning and triple antibacterial treatment in a continuous and automatic manner.

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.

Adaptation response of Pseudomonas fragi on refrigerated solid matrix to a moderate electric field

BACKGROUND

Moderate electric field (MEF) technology is a promising food preservation strategy since it relies on physical properties-rather than chemical additives-to preserve solid cellular foods during storage. However, the effectiveness of long-term MEF exposure on the psychrotrophic microorganisms responsible for the food spoilage at cool temperatures remains unclear.

RESULTS

The spoilage-associated psychrotroph Pseudomonas fragi MC16 was obtained from pork samples stored at 7 °C. Continuous MEF treatment attenuated growth and resulted in subsequent adaptation of M16 cultured on nutrient agar plates at 7 °C, compared to the control cultures, as determined by biomass analysis and plating procedures. Moreover, intracellular dehydrogenase activity and ATP levels also indicated an initial effect of MEF treatment followed by cellular recovery, and extracellular β-galactosidase activity assays indicated no obvious changes in cell membrane permeability. Furthermore, microscopic observations using scanning and transmission electron microscopy revealed that MEF induced sublethal cellular injury during early treatment stages, but no notable changes in morphology or cytology on subsequent days.

CONCLUSION

Our study provides direct evidence that psychrotrophic P. fragi MC16 cultured on nutrient agar plates at 7 °C are capable of adapting to MEF treatment.

Alanine racemase is essential for the growth and interspecies competitiveness of Streptococcus mutans

D-alanine (D-Ala) is an essential amino acid that has a key role in bacterial cell wall synthesis. Alanine racemase (Alr) is a unique enzyme that interconverts L-alanine and D-alanine in most bacteria, making this enzyme a potential target for antimicrobial drug development. Streptococcus mutans is a major causative factor of dental caries. The factors involved in the survival, virulence and interspecies interactions of S. mutans could be exploited as potential targets for caries control. The current study aimed to investigate the physiological role of Alr in S. mutans. We constructed alr mutant strain of S. mutans and evaluated its phenotypic traits and interspecies competitiveness compared with the wild-type strain. We found that alr deletion was lethal to S. mutans. A minimal supplement of D-Ala (150 μg·mL-1) was required for the optimal growth of the alr mutant. The depletion of D-alanine in the growth medium resulted in cell wall perforation and cell lysis in the alr mutant strain. We also determined the compromised competitiveness of the alr mutant strain relative to the wild-type S. mutans against other oral streptococci (S. sanguinis or S. gordonii), demonstrated using either conditioned medium assays or dual-species fluorescent in situ hybridization analysis. Given the importance and necessity of alr to the growth and competitiveness of S. mutans, Alr may represent a promising target to modulate the cariogenicity of oral biofilms and to benefit the management of dental caries.

A Novel In Vitro System for Comparative Analyses of Bone Cells and Bacteria under Electrical Stimulation

Electrical stimulation is a promising approach to enhance bone regeneration while having potential to inhibit bacterial growth. To investigate effects of alternating electric field stimulation on both human osteoblasts and bacteria, a novel in vitro system was designed. Electric field distribution was simulated numerically and proved by experimental validation. Cells were stimulated on Ti6Al4V electrodes and in short distance to electrodes. Bacterial growth was enumerated in supernatant and on the electrode surface and biofilm formation was quantified. Electrical stimulation modulated gene expression of osteoblastic differentiation markers in a voltage-dependent manner, resulting in significantly enhanced osteocalcin mRNA synthesis rate on electrodes after stimulation with 1.4V_RMS. While collagen type I synthesis increased when stimulated with 0.2V_RMS, it decreased after stimulation with 1.4V_RMS. Only slight and infrequent influence on bacterial growth was observed following stimulations with 0.2V_RMS and 1.4V_RMS after 48 and 72 h, respectively. In summary this novel test system is applicable for extended in vitro studies concerning definition of appropriate stimulation parameters for bone cell growth and differentiation, bacterial growth suppression, and investigation of general effects of electrical stimulation.

Itraconazole suppresses the growth of glioblastoma through induction of autophagy: involvement of abnormal cholesterol trafficking

Glioblastoma is one of the most aggressive human cancers with poor prognosis, and therefore a critical need exists for novel therapeutic strategies for management of glioblastoma patients. Itraconazole, a traditional antifungal drug, has been identified as a novel potential anticancer agent due to its inhibitory effects on cell proliferation and tumor angiogenesis; however, the molecular mechanisms involved are still unclear. Here, we show that itraconazole inhibits the proliferation of glioblastoma cells both in vitro and in vivo. Notably, we demonstrate that treatment with itraconazole induces autophagic progression in glioblastoma cells, while blockage of autophagy markedly reverses the antiproliferative activities of itraconazole, suggesting an antitumor effect of autophagy in response to itraconazole treatment. Functional studies revealed that itraconazole retarded the trafficking of cholesterol from late endosomes and lysosomes to the plasma membrane by reducing the levels of SCP2, resulting in repression of AKT1-MTOR signaling, induction of autophagy, and finally inhibition of cell proliferation. Together, our studies provide new insights into the molecular mechanisms regarding the antitumor activities of itraconazole, and may further assist both the pharmacological investigation and rational use of itraconazole in potential clinical applications.