<i>In vitro</i> and <i>in vivo</i> evaluation of diethyldithiocarbamate with copper ions and its liposomal formulation for the treatment of <i>Staphylococcus aureus</i> and <i>Staphylococcus epidermidis</i> biofilms.

Abstract

Surgical site infections (SSIs) are mainly caused by <i>Staphylococcus aureus</i> (<i>S. aureus</i>) and <i>Staphylococcus epidermidis</i> (<i>S. epidermidis</i>) 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 <i>in vitro</i> efficacy of the Cu(DDC)₂ complex (2:1 M ratio of diethyldithiocarbamate (DDC^-) and Cu²⁺) with additional Cu²⁺ against <i>S. aureus</i> and <i>S. epidermidis</i> biofilms in models mimicking SSIs and <i>in vitro</i> antibacterial activity of a liposomal Cu(DDC)₂ + Cu²⁺ formulation. The <i>in vitro</i> activity on <i>S. aureus</i> and <i>S. epidermidis</i> biofilms grown on two hernia mesh materials and in a wound model was determined by colony forming unit (CFU) counting. Cu²⁺-liposomes and Cu(DDC)₂-liposomes were prepared, and their antibacterial activity was assessed <i>in vitro</i> using the alamarBlue assay and CFU counting and <i>in vivo</i> using a <i>Galleria mellonella</i> infection model. The combination of 35 μM DDC^- and 128 μM Cu²⁺ inhibited <i>S. aureus</i> and <i>S. epidermidis</i> biofilms on meshes and in a wound infection model. Cu(DDC)₂-liposomes + free Cu²⁺ displayed similar antibiofilm activity to free Cu(DDC)₂ + Cu²⁺, and significantly increased the survival of <i>S. epidermidis</i>-infected larvae. Whilst Cu(DDC)₂ + Cu²⁺ showed substantial antibiofilm activity <i>in vitro</i> against clinically relevant biofilms, its application in mammalian <i>in vivo</i> models is limited by solubility. The liposomal Cu(DDC)₂ + Cu²⁺ formulation showed antibiofilm activity <i>in vitro</i> and antibacterial activity and low toxicity in <i>G. mellonella</i>, making it a suitable water-soluble formulation for future application on infected wounds in animal trials.