New Insight into Daptomycin Bioavailability and Localization in Staphylococcus aureus Biofilms by Dynamic Fluorescence Imaging

ABSTRACTStaphylococcus aureusis one of the most frequent pathogens responsible for biofilm-associated infections (BAI), and the choice of antibiotics to treat these infections remains a challenge for the medical community. In particular, daptomycin has been reported to fail against implant-associatedS. aureusinfections in clinical practice, while its association with rifampin remains a good candidate for BAI treatment. To improve our understanding of such resistance/tolerance toward daptomycin, we took advantage of the dynamic fluorescence imaging tools (time-lapse imaging and fluorescence recovery after photobleaching [FRAP]) to locally and accurately assess the antibiotic diffusion reaction in methicillin-susceptible and methicillin-resistantS. aureusbiofilms. To provide a realistic representation of daptomycin action, we optimized anin vitromodel built on the basis of our recently publishedin vivomouse model of prosthetic vascular graft infections. We demonstrated that at therapeutic concentrations, daptomycin was inefficient in eradicating biofilms, while the matrix was not a shield to antibiotic diffusion and to its interaction with its bacterial target. In the presence of rifampin, daptomycin was still present in the vicinity of the bacterial cells, allowing prevention of the emergence of rifampin-resistant mutants. Conclusions derived from this study strongly suggest thatS. aureusbiofilm resistance/tolerance toward daptomycin may be more likely to be related to a physiological change involving structural modifications of the membrane, which is a strain-dependent process.