Exploring the anti-biofilm activity of zosteric acid via high-throughput screening of a small molecules scaffold-based library

The understanding of the interaction of microbes with surfaces is the basis for managing emerging threats, ranging from recalcitrant infectious diseases to food safety. While these may be viewed as assorted items, they actually have a common denominator: the biofilm lifestyle. Nowadays, the worldwide safety is seriously jeopardized by the emergence and spread of microorganisms in form of biofilm that are resistant to traditional biocides (Flemming, 2011). In addition, the antimicrobial arena is experiencing a shortage of lead compounds progressing into both clinical and industrial trials (Lam 2007). An innovative approach is the use of biocide-free antibiofilm agents with novel targets, unique modes of action and properties that are different from those of the currently used antimicrobials. Using bio-inspired molecules at sub-lethal concentrations is an elegant way to interfere with specific key-steps that orchestrate biofilm formation, disarming the microorganism without affecting its existence, sidestepping drug resistance and extending the efficacy of the current arsenal of antimicrobial agents. At present, the main bottleneck to the spread and use of this technology is the incorporation of the antibiofilm molecule into a system able to resist to biofilm over a working timescale. The ideal approach would create a permanently non-leaching, long-lasting bio-hybrid material by covalent functionalization of its surface with the anti-biofilm compound. In our previous research, we demonstrated that zosteric acid (ZA), the secondary metabolite produced by the seagrass Zostera marina, might be suitable for implementation as a preventive or integrative approach against biofilm (Villa et al, 2011, Villa et al, 2013). The goal of this work was to understand the structural characteristics responsible for the anti-biofilm activity of ZA in order to identify the binding site of the molecule for immobilizing ZA on an abiotic surface allowing its bioactive moiety to exert the anti-biofilm action (http://www.anfomat.unimi.it/). To this end, a small synthetic compounds library of around 50 molecules, related to the scaffold of ZA, was synthesized. These compounds were subjected to high-throughput biological screening to evaluate both their toxicity and anti-biofilm performance against Escherichia coli and Candida albicans, used as model systems of bacterial and fungal biofilm respectively. The dataset was made by more than 5000 data obtained from biofilm assay assessed quantitatively using fluorochrome-labelled cells in black microplate wells.