Direct Electric Current Treatment under Physiologic Saline Conditions Kills Staphylococcus epidermidis Biofilms via Electrolytic Generation of Hypochlorous Acid

Abstract

The purpose of this study was to investigate the mechanism by which a direct electrical current reduced the viability of Staphylococcus epidermidis biofilms in conjunction with ciprofloxacin at physiologic saline conditions meant to approximate those in an infected artificial joint. Biofilms grown in CDC biofilm reactors were exposed to current for 24 hours in 1/10th strength tryptic soy broth containing 9 g/L total NaCl. Dose-dependent log reductions up to 6.7 log10 CFU/cm2 were observed with the application of direct current at all four levels (0.7 to 1.8 mA/cm2) both in the presence and absence of ciprofloxacin. There were no significant differences in log reductions for wells with ciprofloxacin compared to those without at the same current levels. When current exposures were repeated without biofilm or organics in the medium, significant generation of free chlorine was measured. Free chlorine doses equivalent to the 24 hour endpoint concentration for each current level were shown to mimic killing achieved by current application. Current exposure (1.8 mA/cm2) in medium lacking chloride and amended with sulfate, nitrate, or phosphate as alternative electrolytes produced diminished kills of 3, 2, and 0 log reduction, respectively. Direct current also killed Pseudomonas aeruginosa biofilms when NaCl was present. Together these results indicate that electrolysis reactions generating hypochlorous acid from chloride are likely a main contributor to the efficacy of direct current application. A physiologically relevant NaCl concentration is thus a critical parameter in experimental design if direct current is to be investigated for in vivo medical applications.

Antibiofilm Activity of Low-Amperage Continuous and Intermittent Direct Electrical Current

“…It is also possible that direct electrical current enhances repulsive forces between bacteria and surface materials (20)(21)(22)(23)(24). Additional factors that could affect biofilm integrity include changes in the pH (4,25), temperature (25), and/or concentration of chlorine, nitrogen, and/or hydrogen ions (4,25,26), when applying the low amperage direct current. Sandvik et al recently showed that electrolysis creates hypochlorous acid from chloride in solution, which aides direct electrical current in reducing S. epidermidis and P. aeruginosa biofilms (4).…”

“…Before considering such approaches, however, potential toxicity will need to be addressed (4,5), and a strategy that results in biofilm eradication and not just reduction adopted.…”

“…In these experiments, 200 A was intermittently delivered to test chambers containing S. aureus IDRL-4284, S. epidermidis Xen 43, or P. aeruginosa Xen 5 biofilm-laden Teflon or titanium discs via stainless steel electrodes for 4 days. The computer controlled current source was programmed to deliver current for 4 days of 200 A for 24,12,8,6,4, or 2 h/day. After treatment, the discs were quantitatively cultured, and the LRF was calculated.…”

Antibiofilm Activity of Electrical Current in a Catheter Model

“…Oxidative stress (26)(27)(28)(29)(30), damage to the cell walls (31,32), changes in pH (33,34), and the formation of hypochlorous acid by electrolysis (33) have been proposed. The results generated here support an electrochemical mechanism.…”

Novel methods for debridement of dental implant surfaces contaminated by biofilm

“…There are also possible downstream chemical reactions for other reaction products which could generate reactive oxygen species, 123 or hydrochloric acid. 220 The data from the XTT assay, confocal microscopy and SEM all concur that the greatest biofilm removal is from the cathode, a finding which supporting the concept of chlorine gas being a major contributor. 117 Finally, there is a possibility for electrical effects to be combined with the local application of biocides or with mechanical treatments.…”