The connections between the formation of bacterial biofilms on implants and the immune system of the host have not been investigated in detail. Thus, still little is known on the role of the immune system in the development of implant-associated biofilms produced by S. aureus or P. aeruginosa or other pathogenic bacteria. However, for rational design of treatment strategies, this would be an essential asset.
To develop a mouse model for studying implant-associated infections, we pre-colonized osmotic pumps with S. aureus and implanted them subcutaneously into C57Bl/6 mice. The bacteria expressed a bacterial luciferase which allowed monitoring of their expansion and the development of biofilms by employing noninvasive in vivo imaging. Subsequently, the presence of bacterial aggregates and biofilms on the surface of the implants was showed by immunofluorescence and electron microscopy. Additionally, myeloid cells, including neutrophils and monocytes, had been attracted to the colonized pumps and formed a barrier for the bacteria towards the tissue surrounding the implant. Despite the close neighborhood of bacteria and myeloid cells, no phagocytosis had taken place. Only containment of bacteria to the pumps could be observed. However, activation of myeloid cells had taken place. Depletion of neutrophils led to an enhanced infection and to dissemination of the bacteria from the pumps to the neighboring tissue.