Novel approaches to prevent and treat infections involving staphylococcal biofilms

Bacteria can be found as surface adhered, structured colonies that generate an extracellular matrix, known as a biofilm. Biofilms are recalcitrant to antibiotics. Therefore, treatments of biofilm infections are limited, especially in terms of indwelling medical devices. The major causes of biofilm-associated infections on medical implants are S aureus and S. epidermidis. This work sought to identify and characterise compounds with antistaphylococcal antibiofilm activity. Initial studies were performed as a part of the COATIM consortium. The antibacterial and antibiofilm activity of 56 compounds provided by members of the consortium were assessed against bacterial and fungal organisms. The top five (4-45, CIM008405, P1a-PEP1, P2-5 Tocris 2611) compounds were selected for further characterisation based on their antibiofilm activity and toxicity. The MOA of the five compounds were characterised in S. aureus. All five compounds caused membrane perturbation, but Tocris 2611 was the only one to exhibit some prokaryote selectivity. In addition, Tocris 2611 eradicated preformed staphylococcal biofilms by sterilising the biofilm cells and had low resistance potential. The five compounds were then coated on titanium substrates (representing dental/orthopaedic implants) and tested for their ability to prevent biofilm formation in vitro and in vivo against biofilm colonisation in vivo and in vitro. No useful antibiofilm activity was observed. Finally, three chemical libraries of biologically active small molecules were screened for adjuvants of antibiotics ciprofloxacin and rifamipcin against S. aureus biofilms, and rifampicin, fusidic acid or linezolid against planktonic E. coli. No potentiators were determined against S. aureus biofilms at the tested concentrations. However, several synergistic interactions were initially identified against E. coli, but had limited antibacterial activity against multi-drug resistant (MDR) pathogens. Due to the limitations of current antibiofilm strategies and the ability of bacteria to adapt continuously, it is important to consider combining multiple approaches to target biofilms successfully