In vitro antibacterial activity of hydrogen peroxide and hypochlorous acid, including that generated by electrochemical scaffolds

Hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) are biocides used for cleaning and debriding chronic wound infections, which often harbor drugresistant bacteria. Here, we evaluated the in vitro activity of H2O2 and HOCl against 27 isolates of eight bacterial species involved in wound infections. Minimum inhibitory concentrations (MICs) and minimum biofilm bactericidal concentrations (MBBCs) were measured. Compared to their respective MICs, MBBCs of isolates exposed to H2O2 were 16- to 1,024-fold higher, and those exposed to HOCl were 2- to 4-fold higher. We evaluated the selection of resistance after exposure of Staphylococcus aureus and Pseudomonas aeruginosa biofilms to 10 iterations of electrochemically generated HOCl or H2O2 delivered using electrochemical scaffolds (e-scaffolds), observing no decrease in antibiofilm effects with serial exposure to e-scaffold-generated H2O2 or HOCl. Twenty-four-hour exposure to H2O2-generating e-scaffolds consistently decreased the number of CFU of S. aureus and P. aeruginosa biofilms by ;5.0 log10 and ;4.78 log10 through 10 iterations of exposure, respectively. Four-hour exposure to HOCl-generating e-scaffolds consistently decreased the number of CFU of S. aureus biofilms by ;4.9 log10, and 1-h exposure to HOCl-generating e-scaffolds consistently decreased the number of CFU of P. aeruginosa biofilms by ;1.57 log10. These results suggest that HOCl has similar activity against planktonic and biofilm bacteria whereas the activity of H2O2 is less against biofilm than planktonic bacteria, and that repeat exposure to either biocide, generated electrochemically under the experimental conditions studied, does not lessen antibiofilm effects.