Topical Minocycline Effectively Decontaminates and Reduces Inflammation in Infected Porcine Wounds

Background: Wound infection can impair postoperative healing. Topical antibiotics have potential to treat wound infection and inflammation and minimize the adverse effects associated with systemic antibiotics. Methods: Full-thickness porcine wounds were infected with Staphylococcus-aureus. Using polyurethane wound enclosure devices, wounds were treated with topical 100 mu g/ml minocycline, topical 1000 mu g/ml minocycline, topical saline control, or 4 mg/kg intravenous minocycline. Bacteria were quantified in wound tissue and fluid obtained over 9 hours. Immunosorbent assays were used to analyze inflammatory marker concentrations. Minocycline's effect on in vitro migration and proliferation of human keratinocytes and fibroblasts was tested using scratch assays and metabolic assays, respectively. Results: After 6 hours, 100 and 1000 mu g/ml topical minocycline decreased bacteria in wound tissue to 3.5 +/- 0.87 and 2.9 +/- 2.3 log colony-forming units/g respectively, compared to 8.3 +/- 0.9 log colony-forming units/g in control wounds (p < 0.001) and 6.9 +/- 0.2 log colony-forming units/g in wounds treated with 4 mg/kg intravenous minocycline (p < 0.01). After 2 hours, topical minocycline reduced concentrations of the inflammatory cytokines interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha (p < 0.01), and inflammatory cell counts in wound tissue (p < 0.05). In noninfected wounds, topical minocycline significantly reduced interleukin-1 beta, interleukin-6, and inflammatory cell counts after 4 hours (p < 0.01). Matrix metalloproteinase-9 concentrations decreased after 1-hour treatment (p < 0.05). Keratinocyte and fibroblast in vitro functions were not adversely affected by 10 mu g/ml minocycline or less. Conclusions: Topical minocycline significantly reduces bacterial burden and inflammation in infected wounds compared with wounds treated with intravenous minocycline or control wounds. Minocycline also decreases local inflammation independently of its antimicrobial effect.