The Electricidal Effect: Reduction of Staphylococcus and Pseudomonas Biofilms by Prolonged Exposure to Low-Intensity Electrical Current

Abstract

The activity of electrical current against planktonic bacteria has previously been demonstrated. The shortterm exposure of the bacteria in biofilms to electrical current in the absence of antimicrobials has been shown to have no substantial effect; however, longer-term exposure has not been studied. A previously described in vitro model was used to determine the effect of prolonged exposure (i.e., up to 7 days) to low-intensity (i.e., 20-, 200-, and 2,000-microampere) electrical direct currents on Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis biofilms. Dose-and time-dependent killing was observed. A maximum of a 6-log 10 -CFU/cm 2 reduction was observed when S. epidermidis biofilms were exposed to 2,000 microamperes for at least 2 days. A 4-to 5-log 10 -CFU/cm 2 reduction was observed when S. aureus biofilms were exposed to 2,000 microamperes for at least 2 days. Finally, a 3.5-to 5-log 10 -CFU/cm 2 reduction was observed when P. aeruginosa biofilms were exposed to electrical current for 7 days. A higher electrical current intensity correlated with greater decreases in viable bacteria at all time points studied. In conclusion, low-intensity electrical current substantially reduced the numbers of viable bacteria in staphylococcal or Pseudomonas biofilms, a phenomenon we have labeled the "electricidal effect."The pathogenesis of a wide variety of human infections, including device-related infections, is now recognized to be related to the presence of bacteria in biofilms. The biofilm mode of growth protects bacteria from host defense mechanisms and conventional antimicrobial agents. The development of biofilm-related infections begins with the adhesion of the microorganisms to the biomaterial surface, mediated by the Van der Waals forces, acid-base interactions, and electrostatic forces (28). Electrostatic forces between bacteria and surfaces are generally repulsive, since almost all biomaterials are negatively charged, as are bacteria (19). It has been proposed that these repulsive forces can be enhanced by the application of electrical current, which provokes the surface detachment of bacterial biofilms (26,34,37).The antibacterial activity of electrical current has previously been demonstrated against Staphylococcus aureus and Staphylococcus epidermidis in agar (21, 24); the normal flora on human skin (2); Escherichia coli, Proteus species, and Klebsiella pneumoniae in synthetic urine (5); E. coli, Staphylococcus aureus, and Bacillus subtilis in water (12,22,23); and E. coli in salt solutions (27). The mechanism of the antibacterial activity of electrical current has been suggested to result from toxic substances (e.g., H 2 O 2 , oxidizing radicals, and chlorine molecules) produced as a result of electrolysis (21), the oxidation of enzymes and coenzymes, membrane damage leading to the leakage of essential cytoplasmic constituents (30), and/or a decreased bacterial respiratory rate (22).The aim of the present study was to determine the effect of prolonged exposure (i.e., up to 7 d...

Electrical methods of controlling bacterial adhesion and biofilm on device surfaces

“…Additionally, up to 5-log reductions in Pseudomonas aeruginosa biofilms were observed after 7 days leading to the assertion that long-term exposure to low-intensity current has a notable effect of reducing the numbers of viable CFUs for staphylococcal and pseudomonal biofilms (the electricidal effect). The experiment also demonstrated that higher levels of treatment current and/or longer treatment periods yielded greater reductions in viable biofilm bacteria [82].…”

“…To date, there has been no definitive explanation for the mechanism of electrically induced reductions The most recent and significant advances in the field include the discovery of the "electricidal effect", a long-term reduction in the viability of biofilms using DC electric current without antimicrobials [82,83]. There should be no doubt that del Pozo's recent findings regarding the electricidal effect contribute significant advancements to the therapeutic strategy of electrical bacterial control.…”

“…del Pozo repeated these experiments for prolonged periods (1, 2, 4 and 7 days) on experimental replicates that did not have an antimicrobial in the media [82]. After 2 days, 6-log reductions in the number of viable CFUs for Staphylococcus epidermidis biofilms and 5-log reductions in…”

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“…This community of bacterial cells, embedded in a matrix of extracellular polymeric substance and attached to the foreign body surface, is characterized by high resistance to antibiotics and host defense mechanisms [1,11]. Application of electric current has been shown in vitro to have a direct adverse effect on bacterial biofilms, reducing the number of viable bacteria in a time-dependent and dose-dependent manner [3]. Animal models of implant-associated infections have confirmed the action of electric current against biofilm cells [4,5].…”

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“…When applied to instrumentation in vitro, small electric currents are able to detach biofilm [5,6]. As a result, the bacteria are rendered more susceptible to antibiotics.…”