The efficacy of antibiotics enhanced by electrical currents against Pseudomonas aeruginosa biofilms

Low electrical currents are reported to enhance the activity of tobramycin and biocides against biofilm bacteria. We report that the activity of those antibiotics to which the bacterium is susceptible in its planktonic state may be enhanced by a low electrical current against the more resistant biofilm cells. Pseudomonas aeruginosa biofilms were formed on a dialysis membrane suspended between two parallel electrode plates in an electrical colonisation cell. Ciprofloxacin, polymyxin B and piperacillin were tested on biofilms at ten times their MIC for 12h in the presence of 0 (control) and 9 mA/cm(2) current density. At these concentrations the antibiotics alone reduced the biofilm population, but in the presence of an electrical current the population was further reduced by ciprofloxacin and polymyxin B though not by piperacillin. Exposure of the planktonic bacteria to the same concentrations of antibiotics demonstrated that ciprofloxacin and polymyxin B reduced the population to below 1% after 12h and below 0.1% after 24h, while piperacillin was bacteriostatic. The results suggest that the electrical current can enhance the activity against biofilms of only those antibiotics that are effective against planktonic cells.