Effect of electrical energy on the efficacy of biofilm treatment using the bioelectric effect

Abstract

Background/Objectives:The use of electric fields in combination with small doses of antibiotics for enhanced treatment of biofilms is termed the ‘bioelectric effect’ (BE). Different mechanisms of action for the AC and DC fields have been reported in the literature over the last two decades. In this work, we conduct the first study on the correlation between the electrical energy and the treatment efficacy of the bioelectric effect on Escherichia coli K-12 W3110 biofilms.Methods:A thorough study was performed through the application of alternating (AC), direct (DC) and superimposed (SP) potentials of different amplitudes on mature E. coli biofilms. The electric fields were applied in combination with the antibiotic gentamicin (10 μg/ml) over a course of 24 h, after the biofilms had matured for 24 h. The biofilms were analysed using the crystal violet assay, the colony-forming unit method and fluorescence microscopy.Results:Results show that there is no statistical difference in treatment efficacy between the DC-, AC- and SP-based BE treatment of equivalent energies (analysis of variance (ANOVA) P>0.05) for voltages <1 V. We also demonstrate that the efficacy of the BE treatment as measured by the crystal violet staining method and colony-forming unit assay is proportional to the electrical energy applied (ANOVA P<0.05). We further verify that the treatment efficacy varies linearly with the energy of the BE treatment (r2 =0.984). Our results thus suggest that the energy of the electrical signal is the primary factor in determining the efficacy of the BE treatment, at potentials less than the media electrolysis voltage.Conclusions:Our results demonstrate that the energy of the electrical signal, and not the type of electrical signal (AC or DC or SP), is the key to determine the efficacy of the BE treatment. We anticipate that this observation will pave the way for further understanding of the mechanism of action of the BE treatment method and may open new doors to the use of electric fields in the treatment of bacterial biofilms.

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“…Notably, the application of AC and DC electric fields combined with antibiotics involves a different mechanism 49 than that of the electrochemical biofilm control method proposed in this work.…”

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“…The electrical potentials, provided by either the AC and/or DC signals were significantly smaller than the bulk media electrolysis potential used in previously reported studies of the BE [17][18][19][20][21][24][25][26]. Application of different types of electrical signals of similar energies in combination with the antibiotic gentamicin (10 μg ml −1 ) revealed equivalent reduction of viable Escherichia coli (E. Coli) K-12 W3110 biofilms in a traditional macro-scale setup [29]. Additionally, a linear relationship between the energy of the applied electrical signal and the treatment efficacy of the BE was demonstrated [29].…”

“…Although previous work has shown effective biofilm treatment via the BE, biocompatible treatment methods utilizing voltages below the threshold of biological fluid electrolysis [27] have not been demonstrated [17-21, 23, 25]. Typical electric field intensities demonstrating effective biofilm treatment by the BE have been reported in the range of 2.0-5.0 V cm −1 , corresponding to voltage potentials of 0.8-2.0 V in traditional cuvette apparatuses [17-21, 24, 26, 30] based on the linear relation between electric field and voltage potential for a given electrode spacing [29]. Such voltages are higher than the standard electrolysis potential of biological fluids (~0.82 V at 25 °C, pH 7) [27], resulting in the generation of harmful radical ions and rendering these treatments incompatible for clinical applications.…”

“…Recent work in our group has demonstrated a bioelectric effect that is capable of efficient biofilm treatment requiring voltages well below the media electrolysis potential [28,29]. We demonstrated that the major factor contributing to the enhancement of the BE treatment efficacy was the total electrical energy applied to the biofilms [29]. The electrical potentials, provided by either the AC and/or DC signals were significantly smaller than the bulk media electrolysis potential used in previously reported studies of the BE [17][18][19][20][21][24][25][26].…”

“…Application of different types of electrical signals of similar energies in combination with the antibiotic gentamicin (10 μg ml −1 ) revealed equivalent reduction of viable Escherichia coli (E. Coli) K-12 W3110 biofilms in a traditional macro-scale setup [29]. Additionally, a linear relationship between the energy of the applied electrical signal and the treatment efficacy of the BE was demonstrated [29]. We have also demonstrated real-time micro-scale detection of biofilm growth and inhibition when treated with the BE, using an integrated surface-acoustic-wave (SAW) microsystem [31] .…”