The electricidal effect: reduction of Staphylococcus and pseudomonas biofilms by prolonged exposure to low-intensity...

The activity of electrical current against planktonic bacteria has previously been demonstrated. The short-term 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."