A Nanoscale Characterization of the Interaction of a Novel Alginate Oligomer with the Cell Surface and Motility of Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) biofilm-associated infections are a common cause of morbidity in chronic respiratory disease and represent a therapeutic challenge. Recently, the ability of a novel alginate oligomer (OligoG) to potentiate the effect of antibiotics against gram-negative, multi-drug-resistant bacteria and inhibit biofilm formation in vitro has been described. Interaction of OligoG with the cell surface of PA was characterized at the nanoscale using atomic force microscopy (AFM), zeta potential measurement (surface charge), and sizing measurements (dynamic light scattering). The ability of OligoG to modify motility was studied in motility assays. AFM demonstrated binding of OligoG to the bacterial cell surface, which was irreversible after exposure to hydrodynamic shear (5,500 x g). Zeta potential analysis (pH 5-9; 0.1-0.001 M NaCl) demonstrated that binding was associated with marked changes in the bacterial surface charge (-30.960.8 to -47.0 +/- 2.3 mV; 0.01 M NaCl [pH 5]; P, 0.001). Sizing analysis demonstrated that alteration of surface charge was associated with cell aggregation with a 2-to 3-fold increase in mean particle size at OligoG concentrations greater than 2% (914 +/- 284 to 2599 +/- 472 nm; 0.01MNaCl [pH 5]; P,0.001). These changes were associated with marked dose-dependent inhibition in bacterial swarming motility in PA and Burkholderia spp. The ability of OligoG to bind to a bacterial surface, modulate surface charge, induce microbial aggregation, and inhibit motility represents important direct mechanisms by which antibiotic potentiation and biofilm disruption is affected. These results highlight the value of combining multiple nanoscale technologies to further our understanding of the mechanisms of action of novel antibacterial therapies.