Microbial biofilms are involved in a variety of infections that cannot be cured, as microbes in biofilms resist host immune defences and antibiotic therapies. The overarching purpose of our research is to understand the mechanistic basis of bacterial biofilm formation and biofilm-associated antimicrobial tolerance, and to use this knowledge to develop novel strategies and drug candidates for prevention and treatment of biofilm-based infections. In the talk I will present examples from both our basic science work and more applied work.  
We have developed a Tn-Seq based procedure that enables simultaneous assessment of the relative antibiotic tolerance of hundreds of thousands of individual biofilms, each established by a single transposon mutant. Using this genome-wide Tn-Seq analysis procedure, we found that ciprofloxacin tolerance of Pseudomonas aeruginosa biofilms depends on numerous different genes. The genes that appeared to be most important for ciprofloxacin tolerance have not previously been implicated in antibiotic tolerance of P. aeruginosa biofilms. This includes a gene involved in oxidative stress response, a multidrug efflux pump gene, an ABC transporter gene, and a pilZ domain gene involved in c-di-GMP signalling. Our study emphasizes that biofilm-associated antibiotic tolerance is truly multi-factorial and depends on several genes belonging to different classes.      
We have used high throughput screening to identify chemical compounds that reduce the intracellular c-di-GMP content in P. aeruginosa. This led to the identification of a small molecule, termed H6-335-P1, that efficiently depletes P. aeruginosa for c-di-GMP, inhibits biofilm formation and disperses established biofilms in vitro as well as in animal models of biofilm infection. In addition to the PAO1 laboratory strain, H6-335-P1 was capable of dispersing biofilms of both mucoid, non-mucoid, and a small colony variant clinical P. aeruginosa isolate from a cystic fibrosis patient. A combination of H6-335-P1 with standard of care antibiotics resulted in improved eradication of biofilms in vitro, as well as in two different animal biofilm infection models. Genetic analyses provided evidence that H6-335-P1 specifically stimulates the activity of the c-di-GMP phosphodiesterase BifA in P. aeruginosa. Our work constitutes proof of concept for c-di-GMP phosphodiesterase-activating drugs administered in combination with antibiotics as a viable treatment strategy for otherwise recalcitrant biofilm infections.