Augmentation of antibiotic activity by low-frequency electric and electromagnetic fields examining Staphylococcus aureus in broth media

The use of the electromagnetic field in microbial process bioengineering

An electromagnetic field (EMF) has been shown to have various stimulatory or inhibitory effects on microorganisms. Over the years, growing interest in this topic led to numerous discoveries suggesting the potential applicability of EMF in biotechnological processes. Among these observations are stimulative effects of this physical influence resulting in intensified biomass production, modification of metabolic activity, or pigments secretion. In this review, we present the current state of the art and underline the main findings of the application of EMF in bioprocessing and their practical meaning in process engineering using examples selected from studies on bacteria, archaea, microscopic fungi and yeasts, viruses, and microalgae. All biological data are presented concerning the classification of EMF. Furthermore, we aimed to highlight missing parts of contemporary knowledge and indicate weak spots in the approaches found in the literature.

Using electromagnetic fields to inhibit biofouling and scaling in biogas slurry drip irrigation emitters

Reusing biogas slurry (BS) in agricultural drip irrigation systems may provide a solution to deal with the adverse environmental impacts of applying BS. Biofouling and scaling are two leading issues in drip irrigation emitters. This study investigated a practice that applied electromagnetic fields (EMFs) to control biofilms and scales. The bacterial communities and mineral precipitations in the clogging substances of emitters were determined. Results showed that EMFs inhibited the growth of microbes, and influenced BS physicochemical parameters. Consequently, EMFs shifted the bacterial communities with reduced diversities. Network analyses revealed that bacterial species under EMFs treatments showed lower average connectivities and simpler interactions, which were responsible for the decreases of extracellular polymers substances (EPS). Moreover, EMFs treatments not only reduced the carbonates in emitters, but also prevented the depositions of phosphates, silicates, and quartzes. EMFs also had impacts on the lattice parameters and crystal volumes of carbonates. In addition, the changes in bacterial communities and EPS contents were associated with the reductions of various minerals. Accordingly, EMFs effectively mitigated biofilms and scales with the fixed clogging substances reduced by 29.1-53.8 %. These findings demonstrated that applying EMFs is an effective anti-biofouling and anti-scaling treatment with potential applications in BS irrigation systems.

Low-frequency electromagnetic fields as an alternative to sanitize water of drinking systems in poultry production?

Low-frequency electromagnetic fields (LF-EMF) may present an alternative to conventional sanitation methods of water supply lines in animal production. The objective of this study was to evaluate the effect of the application of LF-EMF on bacterial concentrations and biofilms at scale-models of different drinking systems (circulating and non-circulating) conventionally used in poultry holdings. Treated systems were equipped with commercial devices producing pulsed electromagnetic signals of low frequency up to 10,000 Hz; max. 21 mT. Exposure of water to LF-EMF resulted in changes of the culturable bacterial counts, although with high standard deviations. Differing between systems types, LF-EMF treatment seemed to be responsible either for a limitation or for an increase of colony forming unit counts, with partly statistically significant differences, especially in early stages of treatment. In contrast, neither biofilm formation nor counts of cells suspended in water differed between treated and control lines over 28 days of experiment, as determined by fluorescence microscopy. Although this study indicates that LF-EMF may influence culturability of water microorganisms, no clear inhibitory effects on bacterial biofilm formation or on planktonic microbes by LF-EMF treatment were confirmed in the experiments.

Effects of prolonged exposure to moderate static magnetic field and its synergistic effects with alkaline pH on Enterococcus faecalis

Static magnetic field (SMF) has been shown to biologically affect various microorganisms, but its effects on Enterococcus faecalis, which is associated with multiple dental infections, have not been reported yet. Besides, Enterococcus faecalis was found to be resistant to the alkaline environment provided by a major dental antimicrobial, calcium hydroxide. Therefore, the antibacterial activity of prolonged exposure to moderate SMF (170 mT) and its possible synergistic activity with alkaline pH (pH = 9) were evaluated in the study. The ability to form a biofilm under these conditions was examined by crystal violet assay. Real-time quantitative PCR was performed to evaluate the relative expression of stress (dnaK and groEL) and virulence (efaA, ace, gelE and fsrC) related genes. As the results indicated, cell proliferation was inhibited after 120 h of SMF exposure. What's more, the combined treatment of SMF and alkaline pH showed significantly improved antimicrobial action when compared to single SMF and alkaline pH treatment for more than 24 h and 72 h respectively. However, the ability to form a biofilm was also enhanced under SMF and alkaline pH treatments. SMF can induce stress response by up-regulating the expression of dnaK and elevate virulence gene expression (efaA and ace). These responses were more significant and more genes were up-regulated including groEL, gelE and fsrC when exposed to SMF and alkaline pH simultaneously. Hence, combination of SMF and alkaline pH could be a promising disinfection strategy in dental area and other areas associated with Enterococcus faecalis infections.

Theoretical evidence of maximum intracellular currents versus frequency in an Escherichia coli cell submitted to AC voltage

In this work, the problem of intracellular currents in longilinear bacteria, such as Escherichia coli, suspended in a physiological medium and submitted to a harmonic voltage (AC), is analyzed using the Finite-Element-based software COMSOL Multiphysics. Bacterium was modeled as a cylindrical capsule, ended by semi-spheres and surrounded by a dielectric cell wall. An equivalent single-layer cell wall was defined, starting from the well-recognized three-shell modeling approach. The bacterium was considered immersed in a physiological medium, which was also taken into account in the modeling. A new complex transconductance was thus introduced, relating the complex ratio between current inside the bacterium and voltage applied between two parallel equipotential planes, separated by a realistic distance. When voltage was applied longitudinally relative to the bacterium main axis, numerical results in terms of frequency response in the 1-20 MHz range for E. coli cells revealed that transconductance magnitude exhibited a maximum at a frequency depending on the cell wall capacitance. This occurred in spite of the purely passive character of the model and could be explained by an equivalent electrical network giving very similar results and showing special conditions for lateral paths of the currents through the cell wall. It is shown that the main contribution to this behavior is due to the conductive part of the current. Bioelectromagnetics. 38:213-219, 2017. © 2016 Wiley Periodicals, Inc.

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.

Current Trends in Development of Liposomes for Targeting Bacterial Biofilms

Biofilm targeting represents a great challenge for effective antimicrobial therapy. Increased biofilm resistance, even with the elevated concentrations of very potent antimicrobial agents, often leads to failed therapeutic outcome. Application of biocompatible nanomicrobials, particularly liposomally-associated nanomicrobials, presents a promising approach for improved drug delivery to bacterial cells and biofilms. Versatile manipulations of liposomal physicochemical properties, such as the bilayer composition, membrane fluidity, size, surface charge and coating, enable development of liposomes with desired pharmacokinetic and pharmacodynamic profiles. This review attempts to provide an unbiased overview of investigations of liposomes destined to treat bacterial biofilms. Different strategies including the recent advancements in liposomal design aiming at eradication of existing biofilms and prevention of biofilm formation, as well as respective limitations, are discussed in more details.

Characterization of biofilm formation in natural water subjected to low-frequency electromagnetic fields

Electromagnetic field (EMF) treatment has proven to be effective against mineral scaling in water systems. Therefore, it should be assessed for the treatment of other deposits such as biofilms. In this study, a commercial device producing low-frequency EMF (1-10 kHz) was applied to a reactor fed with natural water for 45 days. The treatment promoted the concentration of microorganisms in suspension and limited the amount of sessile microorganisms in the biofilm, as determined by the measurement of total DNA, qPCR and microscopy. The structure of the bacterial community was assessed by t-RFLP and pyrosequencing analysis. The results showed that EMF treatment affected both planktonic and sessile community composition. EMFs were responsible for a shift in classes of Proteobacteria during development of the biofilm. It may be speculated that the EMF treatment affected particle solubility and/or microorganism hydration. This study indicated that EMFs modulated biofilm formation in natural water.

Cathodic Electrical Stimulation Combined With Vancomycin Enhances Treatment of Methicillin-resistant Staphylococcus aureus Implant-associated Infections

BACKGROUND

Effective treatments for implant-associated infections are often lacking. Cathodic voltage-controlled electrical stimulation has shown potential as a treatment of implant-associated infections of methicillin-resistant Staphylococcus aureus (MRSA).

QUESTIONS/PURPOSES

The primary purpose of this study was to (1) determine if cathodic voltage-controlled electrical stimulation combined with vancomycin therapy is more effective at reducing the MRSA bacterial burden on the implant, bone, and synovial fluid in comparison to either treatment alone or no treatment controls. We also sought to (2) evaluate the histologic effects of the various treatments on the surrounding bone; and to (3) determine if the cathodic voltage-controlled electrical stimulation treatment had an effect on the mechanical properties of the titanium implant as a result of possible hydrogen embrittlement.

METHODS

Thirty-two adult male Long-Evans rats (Harlan Laboratories, Indianapolis, IN, USA) with surgically placed shoulder titanium implants were infected with a clinical strain of MRSA (NRS70). One week after infection, eight animals received a treatment of cathodic voltage-controlled electrical stimulation at -1.8 V versus Ag/AgCl for 1 hour (STIM), eight received vancomycin twice daily for 1 week (VANCO), eight received the cathodic voltage-controlled electrical stimulation and vancomycin therapy combined (STIM + VANCO), and eight served as controls with no treatment (CONT). Two weeks after initial infection, the implant, bone, and synovial fluid were collected for colony-forming unit (CFU) enumeration, qualitative histological analysis by a pathologist blinded to the treatments each animal received, and implant three-point bend testing.

RESULTS

The implant-associated CFU enumerated from the STIM + VANCO (mean, 3.7 × 10(3); SD, 6.3 × 10(3)) group were less than those from the CONT (mean, 1.3 × 10(6); SD, 2.8 × 10(6); 95% confidence interval [CI] of difference, -4.3 × 10(5) to -9.9 × 10(3); p < 0.001), STIM (mean, 1.4 × 10(6); SD, 2.0 × 10(6); 95% CI of difference, -2.1 × 10(6) to -1.8 × 10(3); p = 0.002), and VANCO (mean, 5.8 x 10(4); SD, 5.7 × 10(4); 95% CI of difference, -6.4 × 10(4) to -1.7 × 10(4); p < 0.001) group. The bone-associated CFU enumerated from the STIM + VANCO group (6.3 × 10(1); SD, 1.1 × 10(2)) were less than those from the CONT (mean, 2.8 × 10(5); SD, 4.8 × 10(5); 95% CI of difference, -9.4 × 10(4) to -5.0 × 10(3); p < 0.001) and STIM (mean, 2.6 × 10(4); SD, 2.5 × 10(4); 95% CI of difference, -4.1 × 10(4) to -1.6 × 10(3); p < 0.001) groups. The VANCO group (4.3 × 10(5); SD, 6.3 × 10(2)) also had lower bone-associated CFU as compared with the CONT (mean 95% CI of difference, -9.3 × 10(4) to -4.5 × 10(3); p < 0.001) and STIM (95% CI of difference, -4.0 × 10(4) to -1.5 × 10(3); p < 0.001) groups. In comparison to the synovial fluid CFU enumerated from the CONT group (mean, 3.3 × 10(4); SD, 6.0 × 10(4)), lower synovial CFU were reported for both the STIM + VANCO group (mean, 4.6 × 10(1); SD, 1.2 × 10(2); 95% CI of difference, -4.9 × 10(3) to -3.0 × 10(2); p < 0.001) and the VANCO group (mean, 6.8 × 10(1); SD, 9.2 × 10(1); 95% CI of difference, -4.9 × 10(3) to -2.8 × 10(2); p = 0.007). The histological analysis showed no discernable deleterious effects on the surrounding tissue as a result of the treatments. No brittle fracture occurred during mechanical testing and with the numbers available, no differences in implant flexural yield strength were detected between the groups.

CONCLUSIONS

In this rodent model, cathodic voltage-controlled electrical stimulation combined with vancomycin is an effective treatment for titanium implant-associated infections showing greater than 99.8% reduction in bacterial burden on the implant, surrounding bone, and synovial fluid as compared with the controls and the stimulation alone groups.

CLINICAL RELEVANCE

Cathodic voltage-controlled electrical stimulation combined with vancomycin may enable successful treatment of titanium orthopaedic implant-associated infections with implant retention. Future studies will focus on optimization of the stimulation parameters for complete eradication of infection and the ability to promote beneficial host tissue responses.

Exposure to extremely low-frequency magnetic field affects biofilm formation by cystic fibrosis pathogens

SUMMARY 

Aims: To evaluate the in vitro effects of extremely low-frequency magnetic field (ELF-MF) on growth and biofilm formation by Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia cepacia and Stenotrophomonas maltophilia strains from cystic fibrosis patients. Materials & methods: The motion of selected ions (Fe, Ca, Cu, Zn, Mg, K, Na) was stimulated by the ion resonance effect, then influence on growth and biofilm formation/viability was assessed by spectrophotometry or viability count. Results: Generally, exposure to ELF-MF significantly increased bacterial growth and affected both biofilm formation and viability, although with differences with regard to ions and species considered. Conclusion: Exposure to ELF-MF represents a possible new approach for treatment of biofilm-associated cystic fibrosis lung infections.

[Urinary calculi and infection]

Infection urinary stones resulting from urease-producing bacteria are composed by struvite and/or carbonate apatite. Bacterial urease splits urea and promotes the formation of ammonia and carbon dioxide leading to urine alkalinization and formation of phosphate salts. Proteus species are urease-producers, whereas a limited number of strains of other Gram negative and positive species may produce urease. Ureaplasma urealyticum and Corynebacterium urealyticum are urease-producers that are not isolated by conventional urine cultures, but require specific tests for identification. Primary treatment requires surgical removal of stones as complete as possible. Extracorporeal and endoscopic treatments are usually preferred, while open surgery is actually limited to few selected cases. Residual stones or fragments should be treated by chemolysis via ureteral catheter or nephrostomy or administration of citrate salts in order to achieve a stone-free renal unit. Postoperatively, recurrent urinary tract infection should be treated with appropriate antibiotic treatment although long-term antibiotic prophylaxis can cause resistance. Urinary acidification has been proposed for the prophylaxis of infection stones, but long-term acidification is difficult to achieve in urine infected by urease-producing bacteria. Urease inhibitors lead to prevention and/or dissolution of stones and encrustations in patients with infection by urea-splitting bacteria, but their use is limited by their toxicity. The administration of citrate salts involves an increase of the value of nucleation pH (pHn), that is the pH value at which calcium and magnesium phosphate crystallization occurs, in a greater way than the corresponding increase in the urinary pH due to its alkalinizing effect and resulting in a reduction of the risk of struvite crystallization. In conclusion prevention of the recurrence of infection stones can be achieved by an integrated approach tailored on the single patient. Complete clearance of the stone must be achieved by primary surgical procedure and residual fragments should be extensively treated. In the case of persistent infection, conservative measures, such as acidification and urease inhibitors or citrate administration, should be adopted to minimize its effect on urinary saturation with respect to struvite.

Effects of rotating magnetic field exposure on the functional parameters of different species of bacteria

The aim of the present study was to determine the effect of the rotating magnetic field (RMF) on the growth, cell metabolic activity and biofilm formation by S. aureus, E. coli, A. baumannii, P. aeruginosa, S. marcescens, S. mutans, C. sakazakii, K. oxytoca and S. xylosus. Bacteria were exposed to the RMF (RMF magnetic induction B = 25-34 mT, RMF frequency f = 5-50 Hz, time of exposure t = 60 min, temperature of incubation 37 °C). The persistence of the effect of exposure (B = 34 mT, f = 50 Hz, t = 60 min) on bacteria after further incubation (t = 300 min) was also studied. The work showed that exposure to RMF stimulated the investigated parameters of S. aureus, E. coli, S. marcescens, S. mutans, C. sakazakii, K. oxytoca and S. xylosus, however inhibited cell metabolic activity and biofilm formation by A. baumannii and P. aeruginosa. The results obtained in this study proved, that the RMF, depending on its magnetic induction and frequency can modulate functional parameters of different species of bacteria.

Effects of low-intensity electromagnetic fields on the proliferation and differentiation of cultured mouse bone marrow stromal cells

BACKGROUND

Electromagnetic fields (EMFs) used in stem-cell tissue engineering can help elucidate their biological principles.

OBJECTIVE

The aim of this study was to investigate the effects of low-intensity EMFs on cell proliferation, differentiation, and cycle in mouse bone marrow stromal cells (BMSCs) and the in vivo effects of EMFs on BMSC.

METHODS

Harvested BMSCs were cultured for 3 generations and divided into 4 groups. The methylthiotetrazole (MTT) assay was used to evaluate cell proliferation, and alkaline phosphatase activity was measured via a colorimetric assay on the 3rd, 7th, and 10th days. Changes in cell cycle also were analyzed on the 7th day, and bone nodule formation was analyzed on the 12th day. Additionally, the expression of the collagen I gene was examined by reverse transcription-polymerase chain reaction (RT-PCR) on the 10th day. The BMSCs of the irradiated group and the control group were transplanted into cortical bone of different mice femurs separately, with poly(lactic-co-glycolic acid) (PLGA) serving as a scaffold. After 4 and 8 weeks, bone the bone specimens of mice were sliced and stained by hematoxylin and eosin separately.

RESULTS

The results showed that EMFs (0.5 mT, 50 Hz) accelerated cellular proliferation, enhanced cellular differentiation, and increased the percentage of cells in the G(2)/M+S (postsynthetic gap 2 period/mitotic phase + S phase) of the stimulation. The EMF-exposed groups had significantly higher collagen I messenger RNA levels than the control group. The EMF + osteogenic medium-treated group readily formed bone nodules. Hematoxylin and eosin staining showed a clear flaking of bone tissue in the irradiated group.

CONCLUSION

Irradiation of BMSCs with low-intensity EMFs (0.5 mT, 50 Hz) increased cell proliferation and induced cell differentiation. The results of this study did not establish a stricter animal model for studying osteogenesis, and only short-term results were investigated. Further study of the mechanism of EMF is needed.