LAUSR

Purpose. The treatment of device‐related infections is challenging and current anti‐microbial compounds have poor anti‐biofilm activity. We aimed to identify and characterize novel compounds effective in the eradication of Staphylococcus aureus biofilms. Methodology. Two novel compounds, MMV665953 {1‐(3‐chloro‐4‐fluorophenyl)‐3‐(3,4‐dichlorophenyl)urea} and MMV665807{5‐chloro‐2‐hydroxy‐N‐[3‐(trifluoromethyl)phenyl]benzamide}, effective in killing S. aureus biofilms, were identified by screening of the open access ’malaria box’ chemical library. The minimum bactericidal concentrations, half‐maximal inhibition concentration (IC50) values and minimal biofilm killing concentrations effective in the killing of biofilm were determined against meticillin‐resistant S. aureus and meticillin‐sensitive S. aureus. Fibrin‐embedded biofilms were grown under in vivo‐relevant conditions, and viability was measured using a resazurin‐conversion assay and confocal microscopy. The potential for the development of resistance and cytotoxicity was also assessed. Results. MMV665953 and MMV665807 were bactericidal against S. aureus isolates. The IC50 against S. aureus biofilms was at 0.15‐0.58 mg l−1 after 24 h treatment, whereas the concentration required to eradicate all tested biofilms was 4 mg l−1, making the compounds more bactericidal than conventional antibiotics. The cytotoxicity against human keratinocytes and primary endothelial cells was determined as IC50 7.47 and 0.18 mg l−1 for MMV665953, and as 1.895 and 0.076 mg l−1 for MMV665807. Neither compound was haemolytic nor caused platelet activation. MMV665953 and MMV665807 derivatives with reduced cytotoxicity exhibited a concomitant loss in anti‐staphylococcal activity. Conclusion. MMV665953 and MMV665807 are more bactericidal against S. aureus biofilms than currently used anti‐staphylococcal antibiotics and represent a valuable structural basis for further investigation in the treatment of staphylococcal biofilm‐related infections.