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

Young Wook Kim,Konstantinos Gerasopoulos,Sowmya Subramanian,Reza Ghodssi,Mariana T Meyer,Hsuan-Chen Wu,Hadar Ben-Yoav,Karen Carter,David Quan,William E Bentley

doi:10.1038/npjbiofilms.2015.16

Young Wook Kim, Konstantinos Gerasopoulos + Show 8 more

Open Access

https://doi.org/10.1038/npjbiofilms.2015.16

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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.

Highlights

Bacterial biofilms are complex communities comprising of bacteria and extracellular matrix.[1,2,3] The composition and organisation of biofilms limits diffusion of molecules, including antibiotics, through the structure and into the biofilm or out to the bulk fluid.[4]
As the total energy of the SP-bioelectric effect’ (BE) was the linear sum of the AC-BE that the electrical energy applied to the treatment in the form of and DC-BE, we investigated the effect of total electrical energy on the DC, AC or SP signals provides the charged antibiotic molecule
Treatment with the AC-BE, DC-BE and the SP-BE resulted in significant reduction in bacterial biomass as compared with the controls (ANOVA Po 0.05)

Summary

Introduction

Bacterial biofilms are complex communities comprising of bacteria and extracellular matrix.[1,2,3] The composition and organisation of biofilms limits diffusion of molecules, including antibiotics, through the structure and into the biofilm or out to the bulk fluid.[4]. A promising method to increase the efficacy of antibiotics on biofilms is a combinatorial treatment based on applying electrical signals in combination with low doses of antibiotic, termed the ‘bioelectric effect’ (BE).[13,14,15] Costerton et al.[9] demonstrated improved biofilm treatment through the application of either direct or alternating current (DC or AC) electric fields.[16,17,18,19,20,21,22,23,24] Details of the fundamental mechanisms of the bioelectric effect are still under investigation, and divergent hypotheses have emerged based on the type of the applied field. In the case of a DC voltage, the generation of radicals owing to media electrolysis is suggested as a principal factor.[17,18,25] In addition, some reports describe enhanced efficacy owing to improved antibiotic binding to biofilms[14,26] and enhanced biofilm detachment[27] from an external

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