Live intramacrophagic Staphylococcus aureus as a potential cause of antibiotic therapy failure: observations in an in vivo mouse model of prosthetic vascular material infections.

Objectives: To evaluate the significant role played by biofilms during prosthetic vascular material infections (PVMIs). Methods: We developed an in vivo mouse model of Staphylococcus aureus PVMI allowing its direct observation by confocal microscopy to describe: (i) the structure of biofilms developed on Dacron® vascular material; (ii) the localization and effect of antibiotics on these biostructures; and (iii) the interaction between bacteria and host tissues and cells during PVMI. Results: In this model we demonstrated that the biofilm structures are correlated to the activity of antibiotics. Furthermore, live S. aureus bacteria were visualized inside the macrophages present at the biofilm sites, which is significant as antibiotics do not penetrate these immune cells. Conclusions: This intracellular situation may explain the limited effect of antibiotics and also why PVMIs can relapse after antibiotic therapy.