The role of viscoelasticity of gel-like biofilms on mechanical clearance by immune cells

Biofilms are communities of bacteria which produce a matrix of extracellular polymeric substances (EPS), providing chemical and mechanical protection against antibiotic treatment and phagocytic clearance by immune cells such as neutrophils. Pseudomonas aeruginosa, an opportunistic human pathogen, produces four major EPS components: polymers pel, psl, and alginate, and extracellular DNA (eDNA). Bacterial strains that overproduce alginate, a negatively charged polysaccharide, can interact with divalent cations such as Ca²⁺ to form a gel-like biofilm structure. Extracellular DNA, also negatively charged, may interact separately with calcium ions to form distinct regions with unique properties within a biofilm. Here we investigate the individual and combined effects of eDNA and alginate on biofilm structure, the impact of polymer-specific enzymes as mechanically compromising agents, and the role of viscoelasticity of calcium-gelled biofilms in the success of mechanical clearance by neutrophils.