Compromising matrix structure to make biofilm bacteria easier to eat

Bacterial biofilms cause persistent and dangerous infections which are resistant to standard antibiotics and the immune system. A biofilm is a community of microbes that are embedded in a matrix of extracellular polymeric substances, or EPS, which protects the microbes from antibiotics and immune cells, making the eradication of biofilm infections difficult. Neutrophils are immune cells that use phagocytosis to engulf and digest microbes. Neutrophils have difficulty engulfing bacteria from the biofilms because of the embedding EPS. To remedy this, we use polymer-specific enzyme treatments matched to the dominant polymer produced by a bacterial strain—these treatments cause changes in the bulk mechanical properties of the biofilm, aiding phagocytosis and leading to higher engulfment rates. We utilize a protection-based assay, wherein bacteria from biofilms which have not been successfully engulfed by neutrophils are killed with antibiotics. The neutrophils can then be lysed and the “surviving” bacteria counted as a proxy for phagocytic success. Biofilms also may be stained with a pH-sensitive dye, which fluoresces in highly acidic environments, like inside a neutrophil, allowing discrimination between bacteria which are fully internalized and those which are bound to a neutrophil’s surface.