Inhibitory effect of direct electric field and HA-ZnO composites on S-aureus biofilm formation

In addressing the issue of prosthetic infection, we demonstrate herein how direct electric field (DC EF) stimulation can effectively inhibit biofilm formation, when pathogenic Staphylococcus aureus (MRSA, USA 300) are grown on HA-xZnO (x=0, 5, 7.5, and 10 wt %) biocomposites in vitro. After bacterial preincubation for 4 h, a low intensity DC EF (1V/cm) was applied for different time periods (t=6, 12, 18, and 24 h). The bacterial viability and biofilm maturation were evaluated by a combination of biochemical assays, fluorescence/confocal microscopy, and flow cytometry. The results confirm a time-dependent and composition-independent decrease in bacterial viability and biofilm formation on HA-xZnO composites w.r.t EF-treated HA. Flow cytometry analysis indicated that 12 h EF application resulted in membrane depolarization of approximate to 35% of S. aureus populations on HA-xZnO composites. The live/dead assay results revealed approximate to 60% decline in viable bacterial numbers with a concomitant 3.5-fold increase in the production of reactive oxygen species (ROS) after 18 h of EF. The loss in bacterial viability and biofilm instability is due to the synergistic bactericidal action of ZnO and EF. Taken together, the use of engineered biomaterial substrate with antimicrobial reinforcement coupled with continuous low intensity EF application can be adopted to treat prosthetic implant associated infection. (c) 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1064-1075, 2016.