Confocal scanning-laser micrograph showing the invasion of a biofilm by PMNs. The PMNs (large red nuclei) have entered the biofilm via the open water channels and have invaded short distances (1–5 μm) into the biofilm. The bacterial cells have been stained with the live/dead BacLight stain (BacLight Bacterial Viability kit; Molecular Probes, Eugene, Oregon, USA) and living bacterial cells (green) are seen in very close proximity (<1 μm) to PMNs. We conclude that PMNs invade biofilms but are virtually inactive in killing sessile cells and resolving biofilm infections. Reproduced with permission from Infection and Immunity (40).