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

Laurine Kaul; Adrian I Abdo; Tom Coenye; Simon Swift; Andrew Zannettino; Regine Süss; Katharina Richter

doi:10.1016/j.bioflm.2023.100130

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

Biofilm. 2023 May 17:5:100130. doi: 10.1016/j.bioflm.2023.100130. eCollection 2023 Dec.

Authors

Laurine Kaul^{1

2

3}, Adrian I Abdo^{1

3}, Tom Coenye⁴, Simon Swift⁵, Andrew Zannettino^{3

6

7}, Regine Süss², Katharina Richter^{1

3

8}

Affiliations

¹ Richter Lab, Department of Surgery, Basil Hetzel Institute for Translational Health Research, University of Adelaide, 37 Woodville Road, Adelaide, SA, 5011, Australia.
² Institute of Pharmaceutical Sciences, Department of Pharmaceutics, University of Freiburg, Sonnenstr. 5, 79104, Freiburg, Germany.
³ Adelaide Medical School, Faculty of Health and Medical Sciences, University of Adelaide, 4 North Terrace, Adelaide, SA, 5000, Australia.
⁴ Laboratory of Pharmaceutical Microbiology, Ghent University, Ottergemsesteenweg 460, 9000, Ghent, Belgium.
⁵ Department of Molecular Medicine and Pathology, University of Auckland, 85 Park Road, Grafton, Auckland, 1023, New Zealand.
⁶ Precision Cancer Medicine Theme, South Australian Health & Medical Research Institute, North Terrace, Adelaide, SA, Australia.
⁷ Central Adelaide Local Health Network, Adelaide, Australia.
⁸ Institute for Photonics and Advanced Sensing, University of Adelaide, Adelaide, Australia.

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 Cu²⁺) with additional Cu²⁺ against S. aureus and S. epidermidis biofilms in models mimicking SSIs and in vitro antibacterial activity of a liposomal Cu(DDC)₂ + Cu²⁺ 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. Cu²⁺-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 Cu²⁺ inhibited S. aureus and S. epidermidis 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 S. epidermidis-infected larvae. Whilst Cu(DDC)₂ + Cu²⁺ 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 + Cu²⁺ 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.

Keywords: Biofilms; Copper ions; Diethyldithiocarbamate; Liposomes; Staphylococcus aureus; Staphylococcus epidermidis; Surgical site infections.