(153d) Evaluating Antimicrobial Drug Formulations on a 3D Biofilm Growth Model Under Simulated In Vivo Conditions

Bacterial biofilms are defined as aggregates of bacteria that are embedded within a self-produced matrix, which consists of extracellular proteins (e.g. actin), DNA, and exopolysaccharides (most notably alginate). It has been demonstrated that formation of these significantly increase the risk of persistent chronic infections due to increased antibiotic resistance, specifically in the setting of cystic fibrosis (CF), where thick mucus acts as a secondary matrix. Traditional microbiology assays consist of 2D biofilms in well plates under static conditions or mild agitation and thus do not represent well the natural environment of biofilm infections. In vivo infection models often utilize beads made from alginate, a natural component of bacterial biofilms, as a substrate to initiate biofilm formation. Alginate beads could provide a more biomimetic 3D biofilm growth model for in vitro studies as a bridge to animal models.

In this study, biofilms formed in alginate beads were incorporated into a novel engineered system where the biofilms can be exposed to pharmacokinetically relevant drug profiles. The system comprises of an engineered perfusion bioreactor where the alginate beads containing P. aeruginosa (PA) are incubated and exposed to different drug profiles. Results demonstrate that viable PA, at concentrations well above 1x10⁷ CFU/bead, were successfully embedded within alginate beads as determined by colony forming unit (CFU) assays. Treatment of the beads with the gold standard antibiotic, tobramycin, at clinically relevant concentrations and an exposure time of 2 hours showed no effect in terms of cell growth, detachment of cells from biofilm, or glucose uptake. However, longer exposure times of over 9 hours, at the same concentrations, produced a significant reduction in glucose consumption and bacteria release from biofilm. These results highlight the importance of drug concentration profile on killing of alginate-embedded biofilms and suggest that our proposed system can serve as a bridge between in vitro and in vivo experiment. Current efforts are being made to test additional exposure times, bacteria strains, antimicrobials, and pharmacokinetic profiles.