Macrophage response to staphylococcal biofilms on crosslinked poly(ethylene) glycol polymer coatings and common biomaterials in vitro

Abstract

Biomaterial-associated-infections (BAI) are serious clinical complications that threaten the longevity of implanted devices and lead to high morbidity and mortality. Poly(ethylene)glycol (PEG) coatings have been studied as a strategy to reduce the incidence of BAI by reducing protein deposition that promotes pathogen adhesion and growth on device surfaces. Despite their effectiveness to reduce protein adsorption and a hundred-fold reduction in bacterial adhesion, PEG-based coatings still facilitate weak bacterial adhesion that can form an initial basis for biofilms. Here, we describe a methodology enabling direct, quantitative and detailed qualitative in situ observation of macrophage morphology, migration and phagocytosis of bacteria. In vitro interaction of macrophages with Staphylococcus epidermidis 3399 adhering to commercial, crosslinked PEG-based coatings (OptiChem®) was compared with fluorinated ethylene propylene, silicone rubber and glass. Adhesion, phagocytosis and migration were studied real-time in a parallel-plate-flow-chamber. Macrophages cultured on OptiChem® coatings showed enhanced migration and phagocytosis of bacteria compared to common biomaterials. Bacterial clearance per macrophage on both inert and reactive OptiChem® coatings were about three times higher than on the common biomaterials studied, corresponding with up to 70% reduction in bacterial numbers on OptiChem®, whereas on the biomaterials less than 40% bacterial reduction was obtained. These findings show that bacterial clearance from cross-linked PEG-based coatings by macrophages is more effective than from common biomaterials, possibly resulting from weak adhesion of bacteria on Optichem®. Moreover, macrophages exhibit higher mobility on Optichem® retaining an improved capability to clear bacteria from larger areas than from other common biomaterials, where they appear more immobilized.