The electricidal effect: Reduction of Staphylococcus and Pseudomonas biofilms by prolonged exposure to low-intensity electrical current

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-log₁₀-CFU/ cm² reduction was observed when S. epidermidis biofilms were exposed to 2,000 microamperes for at least 2 days. A 4- to 5-log₁₀-CFU/ cm² 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/cm² 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.".