Staphylococcus aureus biofilms are clinically relevant playing a major role in various infectious diseases, including osteomyelitis, endocarditis, chronic wounds and chronic sinusitis. As standard medical care frequently fails to eradicate biofilms, novel treatment approaches are urgently needed. Adding to this problem is the universal threat of antibiotic resistance, looming with the overuse of antibiotics. This study proposes a new anti-microbial strategy with a distinctively different mechanism of action to antibiotics.
S. aureus colony biofilms were grown on membrane filters and treated with a novel drug-delivery-system combining the iron-chelator deferiprone (Def, 20 mM) and the haem-analogue gallium-protoporphyrin (GaPP, 250 µg/ml). After 5 days the treatment efficacy was assessed by CFU counting. Cross-sections of colony biofilms were visualised by correlative microscopy using live/dead staining.
The formulations incorporating GaPP and Def-GaPP demonstrated anti-biofilm properties (3.1-fold and 3.8-fold Log10 reduction in CFU/ml, respectively) and were significantly more effective in the elimination of S. aureus biofilms than formulations loaded with the antibiotic ciprofloxacin (CIP, 5 µg/ml, 1.3-fold Log10 reduction). Microscopy images supported the efficacy of Def and GaPP.
In conclusion, this study revealed promising anti-biofilm properties of a novel non-antibiotic treatment against S. aureus biofilms. By interfering with the bacterial iron metabolism, the compounds Def and GaPP exceeded the efficacy of CIP in vitro. The potential for future clinical applications needs to be evaluated.