Abstract
Surgical site infections (SSIs) are mainly caused by Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis) biofilms. Biofilms are aggregates of bacteria embedded in a self-produced matrix that offers protection against antibiotics and promotes the spread of antibiotic-resistance in bacteria. Consequently, antibiotic treatment frequently fails, resulting in the need for alternative therapies. The present study describes the in vitro efficacy of the Cu(DDC)(2) complex (2:1 M ratio of diethyldithiocarbamate (DDC(-)) and Cu(2+)) with additional Cu(2+) against S. aureus and S. epidermidis biofilms in models mimicking SSIs and in vitro antibacterial activity of a liposomal Cu(DDC)(2) + Cu(2+) formulation. The in vitro activity on S. aureus and S. epidermidis biofilms grown on two hernia mesh materials and in a wound model was determined by colony forming unit (CFU) counting. Cu(2+)-liposomes and Cu(DDC)(2)-liposomes were prepared, and their antibacterial activity was assessed in vitro using the alamarBlue assay and CFU counting and in vivo using a Galleria mellonella infection model. The combination of 35 μM DDC(-) and 128 μM Cu(2+) inhibited S. aureus and S. epidermidis biofilms on meshes and in a wound infection model. Cu(DDC)(2)-liposomes + free Cu(2+) displayed similar antibiofilm activity to free Cu(DDC)(2) + Cu(2+), and significantly increased the survival of S. epidermidis-infected larvae. Whilst Cu(DDC)(2) + Cu(2+) showed substantial antibiofilm activity in vitro against clinically relevant biofilms, its application in mammalian in vivo models is limited by solubility. The liposomal Cu(DDC)(2) + Cu(2+) formulation showed antibiofilm activity in vitro and antibacterial activity and low toxicity in G. mellonella, making it a suitable water-soluble formulation for future application on infected wounds in animal trials.