Antibiofilm efficacy of the gold compound auranofin on dual species biofilms of Staphylococcus aureus and Candida sp

Aims: Staphylococcus aureus (a bacterial pathogen) and Candida sp. (opportunistic fungi) are two clinically relevant biofilm-forming microbes responsible for a majority of community- and nosocomial-acquired infections. Dual species biofilm formation between S. aureus and Candida sp. extremely enhances the antimicrobial resistance of the micro-organisms and is difficult to treat with antibiotic therapy. Hence, it is crucial to explore new antimicrobial agents. Auranofin (AF) is a mixed ligand gold compound and has recently been repurposed as an antibacterial and antifungal agent. However, the effects of AF against dual species biofilm have remained largely untested.

Methods and results: In the present study, by constructing biofilms on microplates and urinary catheter surfaces, AF showed strong planktonic cells and biofilm inhibitory effects against mono- and dual culture models of S. aureus and Candida albicans but only exhibited moderate antibiofilm effects on Candida parapsilosis. Auranofin could be synergistic with subminimal inhibitory concentrations of amphotericin B against S. aureus + C. albicans/C. parapsilosis dual biofilms. Auranofin also showed effective antimicrobial effects on vancomycin-resistant strains. However, the antimicrobial effects of AF were decreased in the presence of heat-inactivated foetal bovine serum.

Conclusions: In summary, AF could effectively inhibit S. aureus and C. albicans mono- and dual biofilm formation in vitro.

Significance and impact of the study: Coexistence between Staphylococcus aureus and Candida sp. in dual biofilms leads to increased resistance to some conventionally used antimicrobials, indicating a need for alternative treatments. This study demonstrates the potential for the Au-containing compound AF in the treatment of dual biofilm infections and encourages further investigation of this treatment for clinical use.